A Guide to AP® Chemistry Units & Topics
AP® Chemistry Key Concepts
AP® Chemistry is one of the many science subjects the College Board® has to offer. In 2021, over 130,000 students worldwide took the AP Chemistry exam. The course is aimed to help high-school students develop a strong foundation in chemistry at the college level. Accordingly, you will study college-level chemistry, which encourages the learning of various core science practices and key theories that are vital to the further study of chemical sciences.
In this article, we’ll give you an overview of the units and topics in the AP Chemistry course, which are based on 6 science practices and 4 big ideas. This will give you a fair idea of what you will need to study to ace the AP Chemistry exam.
AP Chemistry Course Overview
The AP Chemistry course is made up of two main components — Science Practices and Course Content. As you progress through the course, you will learn the science practices because they are combined with the course content. These two main components of the AP Chemistry course are interdependent and will be a part of your study material right from the beginning.
The course content itself is broken down into separate units that will teach you an array of topics and concepts in AP Chemistry. These concepts are vital to a strong foundation in chemistry and are what colleges will expect you to master in order to qualify for college credit. Each unit in the course is based on one or more of the 4 big ideas of AP Chemistry. These ideas are nothing but the core concepts that play a key role in the study of chemistry.
The exam contains questions based on these units and science practices at different weights. You can read more about the exam in our AP Chemistry exam guide.
Now, let’s take a closer look at these two components, starting with the science practices.
What are the AP Chemistry Science Practices?
AP Chemistry has a total of six science practices that you will need to master. Simply put, they are skills that you will need to develop to study the various units in the course. Once learned, these skills will improve your critical thinking and analytical ability, which are necessary for further studies in chemistry and also key to doing well on the AP Chemistry exam. The science practices prescribed for this course are woven into each unit to help you learn and practice them better.
Here are the 6 science practices and the skills you will develop by mastering each of them.
-
Models and Representations
Through this science practice, you will develop the skills required to form detailed explanations of models and representations.
Skills you will learn:
- Describe the components and quantitative information within models and representations that showcase properties at the particulate level.
- Describe the components and quantitative information within models and representations that showcase properties at both the particulate level and the macroscopic level.
-
Question and Method
This science practice will enable you to pose scientific questions and determine methods related to chemical procedures.
Skills you will learn:
-
- Identify valid, testable scientific questions based on given data, observations, or models.
- Develop hypotheses or predictions based on experimental results.
- Identify procedures in a scientific experiment based on the developed questions.
- Make observations or gather data from hypothetical laboratory setups or experimental results.
- Identify areas of possible error in an experiment.
- Explain how alterations to an experiment might affect the results.
- Representing Data and Phenomena
This science practice is related to the skill required to create representations of chemical phenomena.
Skills you will learn:
- Use graphs with accurate scales and units to represent chemical phenomena.
- Create representations of chemical substances using models and diagrams.
- Visually represent relationships across different levels and scales, and between structures and interactions.
- Model Analysis
Through this science practice, you will learn how to analyze models and representations, including their interpretation, both on a single scale and across multiple scales.
Skills you will learn:
- Use chemical theories, representations, and models to describe the characteristics or phenomena of atoms and molecules.
- Study and justify whether a model is in agreement with chemical theories.
- Use models and representations to explain connections between particulate and macroscopic level properties of a substance.
- Study and explain how well a representation describes the relationship between particulate and macroscopic level properties.
- Mathematical Routines
This science practice aims at developing your problem-solving skills using mathematical relationships.
Skills you will learn:
- Identify quantities from the given information that can be used to solve a problem.
- Identify theories, definitions, and mathematical relationships that can be used to solve a given problem.
- Explain how changing one variable in an equation affects the other variables.
- Find and use the information provided in a graph to solve problems.
- Develop a balanced equation for a given chemical phenomena.
- Use logical computation pathways to predict or determine an unknown quantity from the given known quantities.
- Argumentation
This science practice will enable you to think of and develop valid explanations or arguments of scientific nature with regard to a given chemical phenomenon.
Skills you will learn:
- Make scientific claims.
- Use experimental data to support the developed claims.
- Use representations or models of particulate-level matter to support claims.
- Use chemical theories and mathematical routines to develop reasoning for the justification of claims.
- Identify relationships between particulate and macroscopic scales and use them to provide justification for claims.
- Explain how the result of a chemical experiment is dependent upon chemical processes and theories.
- Explain how possible sources of error within an experiment could affect the results.
AP Chemistry’s 4 Big Ideas
The big ideas are simply the themes that will be explored as you learn the content taught in the AP Chemistry topics. These big ideas provide the foundation on which the course is structured. The big ideas are interwoven into multiple units and therefore are applied in various contexts. Let’s take a look at each one of these big ideas.
In chemistry, quantities are described at the macroscopic as well as the atomic level. Understanding how to draw relationships between these quantities, within the same scale and across different scales, is vital to developing explanations and making predictions in chemistry.
The units you will study that further elaborate upon this big idea are: Atomic structure and properties, Intermolecular forces and properties, Chemical reactions, and Application of thermodynamics.
The macroscopic properties of chemical substances result from the structure and interactions between the atoms and molecules that make up the substance in question. These observable properties can be predicted from known characteristics of the chemical structure and interactions at the atomic level. Macroscopic properties can also be used to predict structures and interactions.
The units you will study that further elaborate upon this big idea are: Atomic structure and properties, Molecular and ionic compound structure and properties, Intermolecular forces and properties, Acids and bases, and Application of thermodynamics.
Chemical reactions involve the rearrangement of matter. To properly understand these chemical transformations, one needs to study what occurs both at the macroscopic and atomic level during the process. Some of the things that are studied include quantifying the amount of resulting products, visualizing intermolecular forces, and observing the rate of transformation.
The units you will study that further elaborate upon this big idea are: Chemical reactions, Kinetics, and Equilibrium.
Energy plays two essential roles in chemical systems. The first role involves describing the distribution and redistribution of energy among the various components of a system during heat exchange, chemical reactions, and phase transitions. The second role involves identifying the enthalpic and entropic forces that cause chemical processes to occur. These forces affect chemical equilibria and how the equilibrium position shifts in response to changes in experimental conditions.
The units you will study that further elaborate upon this big idea are: Kinetics, Thermodynamics, and Applications of thermodynamics.
Now that you have a better understanding of the science practices and ideas that form the basis of all AP Chemistry units, let’s take a look at each unit and the topics covered.
AP Chemistry Units and Topics
The College Board’s AP Chemistry course and exam description (CED) indicates that the course material is divided into nine units. Each unit will focus on one or more of the four big ideas. These units are further broken down into several topics through which you will learn and master the prescribed science practices. In this section, we’ll look at each of these units, their weighting in the final AP Chemistry exam, and their related topics.
Here are the weightings of each unit on the AP Chemistry exam:
| Units | Unit Name | Exam Weight |
|---|---|---|
| Unit 1 | Atomic Structure and Properties | 7–9% |
| Unit 2 | Molecular and Ionic Compound Structure and Properties | 7–9% |
| Unit 3 | Intermolecular Forces and Properties | 18–22% |
| Unit 4 | Chemical Reactions | 7–9% |
| Unit 5 | Kinetics | 7–9% |
| Unit 6 | Thermodynamics | 7–9% |
| Unit 7 | Equilibrium | 7–9% |
| Unit 8 | Acids and Bases | 11–15% |
| Unit 9 | Applications of Thermodynamics | 7–9% |
Atomic Structure and Properties
Exam Weight: 7–9%㇑Class Periods: 9–10
The first unit introduces the atomic theory of matter as the foundational model used in chemistry to explain the observed properties of chemical substances. You will study macroscopic (large scale) systems (eg, samples of chemical substances measured in a lab) that are made of very large numbers of atoms and molecules and learn how to compare samples using moles, which is a molecular counting unit that relates a macroscale system to the number of molecules present at the atomic scale. In addition to this, you will also learn about the information contained in the periodic table and how it is organized, including predictable patterns in the atomic structure, electron configuration, properties, and reactivity (ie, the periodicity) of the elements in relation to their atomic number and position on the periodic table.
The big ideas explored in this unit are:
- Big Idea 1: Scale, Proportion, and Quantity – Chemistry examines quantities and their proportions on both the macroscopic and atomic scales. How are the macroscopic and atomic scales related?
- Big Idea 2: Structure and Properties – How can the same element form two entirely different materials?
| Topics | Objective | Suggested Science Practice |
|---|---|---|
| 1.1 Moles and Molar Mass | Learn how to use dimensional analysis and the mole concept to calculate the number of atoms or molecules in a given amount of a substance. | 5. Mathematical Routines |
| 1.2 Mass Spectroscopy of Elements | Learn to quantitatively explain the relationship between an element’s mass spectrum and the masses of the element’s isotopes. | 5. Mathematical Routines |
| 1.3 Elemental Composition of Pure Substances | Explain in quantitative terms how the elemental composition (percentage by mass) and the empirical formula of a pure substance are related. | 2. Question and Method |
| 1.4 Composition of Mixtures | Learn to identify a sample as either a pure substance or a mixture based on its composition in either qualitative or quantitative terms. | 5. Mathematical Routines |
| 1.5 Atomic Structure and Electronic Configuration | Learn to use the Aufbau principle to create symbolic representations of the electron configurations of atoms and their ions. | 1. Models and Representations |
| 1.6 Photoelectron Spectroscopy | Learn to use the photoelectron spectrum of an atom or ion to determine its electron configuration or to determine the energy and number of electrons in a given subshell. | 4. Model Analysis |
| 1.7 Periodic Trends | Explain how the electronic structures of the elements on the periodic table result in the observed atomic properties and periodic trends across the table. | 4. Model Analysis |
| 1.8 Valence Electrons and Ionic Compounds | Learn how periodicity results in trends in the reactivity and chemical properties of elements across the periodic table. | 4. Model Analysis |
If you would like an in-depth study of the components of Unit 1, you can read our article on AP Chemistry Unit 1: Atomic Structure and Properties.
Molecular and Ionic Compound Structure and Properties
Exam Weight: 7–9%㇑Class Periods: 12–13
The physical and chemical properties of a substance are the result of how its particles (ie, atoms, ions, or molecules) are bonded together (ie, its chemical structure) and how its structural units are arranged by the forces acting between them. In this unit, you will learn about chemical bonds and how they differ from ordinary intermolecular forces as well as how to use electronegativity to make predictions about the type of bond that will form between two atoms. You will also learn about how structural features and attractive forces at the atomic level influence the properties of a substance at the macroscopic level.
The big idea explored in this unit is:
- Big Idea 2: Structure and Properties – How are molecular structures arranged, and how has the discovery of highly structured molecules such as DNA impacted the world?
| Topics | Objective | Suggested Science Practice |
|---|---|---|
| 2.1 Types of Chemical Bonds | Explain how the type of bond that forms between two atoms relates to the properties of the elements joined by the bond. | 6. Argumentation |
| 2.2 Intramolecular Force and Potential Energy | Study the factors that affect the strength of the interaction between two atoms and describe the interaction in terms of potential energy as a function of the distance between atoms. | 3. Representing Data and Phenomena |
| 2.3 Structure of Ionic Solids | Learn to make or interpret a particulate model of an ionic solid that follows Coulomb’s Law. | 4. Model Analysis |
| 2.4 Structure of Metal and Alloys | Learn to make or interpret models of metallic solids and alloys with key structural features and interactions represented. | 4. Model Analysis |
| 2.5 Lewis Diagrams | Learn to make or interpret Lewis diagrams that represent molecules. | 3. Representing Data and Phenomena |
| 2.6 Resonance and Formal Change | Learn to make or interpret Lewis diagrams that represent resonance between equivalent structures or that allow the use of formal charge to evaluate the most stable configuration among nonequivalent structures. | 6. Argumentation |
| 2.7 VSEPR and Bond Hybridization | Explain a molecule’s structural and electron properties using VSEPR theory and Lewis diagrams. | 6. Argumentation |
To learn more about this unit, check out our article AP Chemistry Unit 2: Molecular and Ionic Compound Structure and Properties.
Intermolecular Forces and Properties
Exam Weight: 18–22%㇑Class Periods: 14–15
The properties of solids, liquids, and gasses are determined by the arrangement of particles within a substance at that particular state, the relative mobility of the particles, and the kind of interactions between particles. Physical changes from one form of matter to another (eg, changing to a solid, liquid, or gas) are strongly influenced by the particle size, shape, spacing, and the forces acting between them. In this unit, you will learn about the relationship between the macroscopic properties of solids, liquids, and gasses in relation to the particle structure on the atomic and molecular scale.
The big ideas explored in this unit are:
- Big Idea 1: Scale, Proportion, and Quantity – How are mixtures affected by particle interactions?
- Big Idea 2: Structure and Properties – Describe the properties of solids, liquids, and gasses on the atomic scale, study how the molecular structure of a chemical component affects its properties as either a pure substance or in a mixture; and explain situations that are dependent on the properties of liquids and solids.
| Topics | Objective | Suggested Science Practice |
|---|---|---|
| 3.1 Intermolecular Forces | Explain how molecular structure determines the strength and type of intermolecular force acting between molecules of same chemical species or between molecules of two different species. | 4. Model Analysis |
| 3.2 Properties of Solids | Explain how the macroscopic properties of a substance depend on its particle-level structure and the interactions between them. | 4. Model Analysis |
| 3.3 Solids, Liquids, and Gasses | Learn to use particle diagrams and models to describe and explain the differences between the solid, liquid, and gaseous states of matter. | 3. Representing Data and Phenomena |
| 3.4 Ideal Gas Law | Use the ideal gas law to determine the properties of a gas (or mixture of gasses) at the macroscopic level. | 5. Mathematical Routines |
| 3.5 Kinetic Molecular Theory | Use kinetic molecular theory (KMT), particulate models, and graphical representations to describe the relationship between particle movement and a gas’s macroscopic properties. | 4. Model Analysis |
| 3.6 Deviation from Ideal Gas Law | Explain how attractive interactions between gas particles and the non-zero gas particle volumes can result in nonideal behaviors in gasses and identify the conditions that promote non-ideal behavior. | 6. Argumentation |
| 3.7 Solutions and Mixtures | Learn the properties of a solution and how to use the definition of molar concentration (molarity) to relate the number (moles) of solute particles to the volume of a solution. | 5. Mathematical Routines |
| 3.8 Representations of Solutions | Learn how to use particle diagrams to represent the interactions and concentrations of chemical species within a solution mixture. | 3. Representing Data and Phenomena |
| 3.9 Separation of Solutions and Mixtures Chromatography | Learn how chromatography, distillation, and other separation methods use the differences in the strength of the interactions between chemical species to achieve the separation of the components of a solution. | 2. Question and Method |
| 3.10 Solubility | Explain the solubility of chemical compounds in both aqueous and nonaqueous solvents based on the presence (or absence) of interactions between the compound and solvent particles. | 4. Model Analysis |
| 3.11 Spectroscopy and the Electromagnetic Spectrum | Learn the specific types of molecular and electronic transitions that are caused within molecules by each region of the electromagnetic spectrum. | 4. Model Analysis |
| 3.12 Photoelectric Effect | Explain how the energy of a photon that has been absorbed or emitted by an atom or molecule relates to the corresponding electronic transition that occurs in the atom or molecule. | 5. Mathematical Routines |
| 3.13 Beer-Lambert Law | Use the Beer-Lambert Law to explain how the absorption of light by a solution is related to concentration, path length, and molar absorptivity. | 2. Question and Method |
While this is just an outline, we’ve also put together a detailed breakdown of this unit in our article AP Chemistry Unit 3: Intermolecular Forces and Properties.
Chemical Reactions
Exam Weight: 7–9%㇑Class Periods: 14–15
Matter can undergo chemical transformations in processes that are referred to as ‘chemical reactions’. In this unit, you will explore how these chemical reactions occur, how they involve the making and breaking of chemical bonds, and how chemical reactions between substances alter the properties of these substances as they change from reactants to products. Many properties of matter can be identified by the strength of the chemical bonds within molecules and by the intermolecular interactions between molecules. You will study these properties and how they change after a chemical reaction. In addition, you will also learn how to represent these reactions as chemical equations, how to balance chemical equations, and how balanced chemical equations are used to understand the changes that occur at the atomic level.
The big ideas explored in this unit are:
- Big Idea 1: Scale, Proportion, and Quantity – A chemical reaction causes firecrackers to explode.
- Big Idea 3: Transformation – The processes that occur during chemical reactions lead to changes in a substance.
| Topics | Objective | Suggested Science Practice |
|---|---|---|
| 4.1 Introduction for Reactions | Learn to identify the difference between physical and chemical changes in matter. | 2. Questions and Method |
| 4.2 Net Ionic Equations | Learn to write and balance full chemical equations or net ionic equations to describe changes in matter. | 5. Mathematical Routines |
| 4.3 Representations of Reactions | Learn to use particulate models to represent and describe chemical reactions or physical reactions at the molecular and atomic level. | 3. Representing Data and Phenomena |
| 4.4 Physical and Chemical Changes | Learn about the relationship between changes in bond interactions and the macroscopic properties of a substance. | 6. Argumentation |
| 4.5 Stoichiometry | Learn to use balanced chemical equations to calculate how changes in the quantities of reactants consumed affect the resulting quantities of products produced by a chemical reaction. | 5. Mathematical Routines |
| 4.6 Introduction to Titration | Learn how to use titrations to find a solution’s equivalence point, which occurs when a reactant has been completely consumed by a chemical reaction, and how to use this equivalence point to calculate the starting amount of reactant. | 3. Representing Data and Phenomena |
| 4.7 Types of Chemical Reactions | Learn to identify chemical reactions as:
| 1. Models and Representations |
| 4.8 Introduction to Acid-Base Reactions | Learn to identify chemical species as:
| 1. Models and Representations |
| 4.9 Oxidation-Reduction (Redox) Reactions | Learn to use half-reactions to balance redox reactions, which involve the transfer of electrons. | 5. Mathematical Routines |
To learn more about the concepts you will be introduced to in this unit, take a look at our article on AP Chemistry Unit 4 – Chemical Reactions.
Kinetics
Exam Weight: 7–9%㇑Class Periods: 13–14
Chemical changes occur at varying rates based on the frequency of specific high-energy molecular collisions. There are many factors that affect this frequency, and therefore also affect the rate at which chemical reactions take place. Some of these factors include the environment, the temperature, the amount of reactants, and the presence or absence of catalysts. You will learn how to measure the rates of chemical reactions using given information, such as the changes in concentration of reactants or products or even the change in energy over time.
The big ideas explored in this unit are:
- Big Idea 3: Transformations – Understand why different reactions occur at different rates.
- Big Idea 4: Energy – What causes bread to rise?
| Topics | Objective | Suggested Science Practice |
|---|---|---|
| 5.1 Reaction Rates | Learn how the parameters of an experiment, such as temperature or reactant concentration, affect the rate at which a chemical reaction takes place. | 6. Argumentation |
| 5.2 Introduction to Rate Law | Learn to use experimental data to determine rate constants and reaction order to create a rate law equation for a given chemical reaction. | 5. Mathematical Routines |
| 5.3 Concentration Changes Over Time | Learn to interpret graphs showing experimental measurements of chemical concentrations vs time to determine rate orders and the rate law equation for a given chemical reaction. | 5. Mathematical Routines |
| 5.4 Elementary Reactions | Learn to use stoichiometry to determine the rate law expression for elementary reactions. | 5. Mathematical Routines |
| 5.5 Collision Model | Learn to explain how the frequency, orientation, and energy of molecular collisions relate to the rate of a reaction. | 6. Argumentation |
| 5.6 Reaction Energy Profile | Learn how to use reaction energy profiles to show a reaction’s activation energy and the overall change in energy between reactants and products. | 3. Representing Data and Phenomena |
| 5.7 Introduction to Reaction Mechanics | Learn how elementary reactions combine to form the reaction mechanism of a more complex, multistep reaction. | 1. Models and Representations |
| 5.8 Reaction Mechanism and Rate Law | Learn to determine the rate law for more multistep reactions whose first step is a rate-limiting elementary reaction. | 5. Mathematical Routines |
| 5.9 Steady-State Approximation | Learn to determine the rate law for more multistep reactions whose rate-limiting elementary reaction is not the first step. | 5. Mathematical Routines |
| 5.10 Multistep Reaction Energy Profile | Learn to depict the reaction energy profiles of multistep reactions, showing the activation energy and overall energy change of the reaction. | 3. Representing Data and Phenomena |
| 5.11 Catalysis | Learn how catalysts affect reactions by altering activation energy and/or reaction mechanisms. | 6. Argumentation |
If you’re looking for a more detailed study guide of this unit, read our article AP Chemistry Unit 5 – Kinetics.
Thermodynamics
Exam Weight: 7–9%㇑Class Periods: 10–11
Thermodynamics describes the role of energy in a chemical reaction, and knowledge of thermodynamics helps to predict the direction in which chemical reactions proceed. The availability and release of energy forms the basis of any chemical reaction, because energy is needed as some bonds break and is released as other bonds form. The laws of thermodynamics allow us to understand this role of energy in chemical processes, which include the transfer and conversion of energy in its various forms, such as heat and work. This unit will focus on thermodynamics and how thermodynamics affects the favorability of chemical reactions.
The big idea explored in this unit is:
- Big Idea 4: Energy – How the making or breaking of chemical bonds is affected by energy.
| Topics | Objective | Suggested Science Practice |
|---|---|---|
| 6.1 Endothermic and Exothermic Processes | Learn how energy changes from chemical and physical changes are related to macroscopic experimental observations and measurements, such as changes in temperature. | 6. Argumentation |
| 6.2 Energy Diagrams | Learn to use energy diagrams to represent physical or chemical changes and the gain or loss of energy. | 3. Representing Data and Phenomena |
| 6.3 Heat Transfer and Thermal Equilibrium | Learn how molecular collisions are influenced by the amount of thermal energy available. | 6. Argumentation |
| 6.4 Heat Capacity and Calorimetry | Learn how to use calorimetry experiments to calculate the heat (q) absorbed or released by a chemical system. | 2. Question and Method |
| 6.5 Energy of Phase Changes | Learn about the molar enthalpy of phase transitions and how heat (q) is absorbed or released as substances transition between different states of matter. | 1. Models and Representations |
| 6.6 Introduction to Enthalpy of Reaction | Learn to calculate the molar enthalpy of a reaction based on the heat (q) released or absorbed for a given amount of reacting substance. | 4. Model Analysis |
| 6.7 Bond Enthalpies | Learn to calculate the overall enthalpy change of a reaction based on the bond energies of the individual bonds that are broken or formed during the reaction. | 5. Mathematical Routines |
| 6.8 Enthalpy of Formation | Learn how to use the standard enthalpies of formation for the individual products and reactants of a reaction to calculate the enthalpy change of the overall reaction. | 5. Mathematical Routines |
| 6.9 Hess’s Law | Learn to represent a physical or chemical process as a sum of multiple steps. Learn to explain how the sum of enthalpies from each individual step is related to the enthalpy of the overall physical or chemical process. | 5. Mathematical Routines |
Want to plan your review of this unit better? Then study our unit guide on AP Chemistry Unit 6 – Thermodynamics.
Equilibrium
Exam Weight: 7–9%㇑Class Periods: 14–16
In this unit, you will learn that interactions between or within molecules can both form and break. In other words, many reactions are reversible. When the forward and reverse reactions in a system occur at the same rate, the system is in equilibrium. Changes in the conditions of the system can change its equilibrium. These changes can include the addition or removal of a chemical substance, temperature fluctuations, or changes in volume. As these conditions change, the rates of the forward and reverse reactions also change, and the system will adjust until the rates are again equal. In this unit you will learn about Le Chȃtelier’s principle, which describes how the equilibrium of a system changes in response to changing conditions.
The big ideas explored in this unit are:
- Big Idea 1: Scale, Proportion, and Quantity – Why doesn’t water run uphill?
- Big Idea 3: Transformation – What makes reactions reversible?
| Topics | Objective | Suggested Science Practice |
|---|---|---|
| 7.1 Introduction to Equilibrium | Learn to explain how observable processes are reversible When equilibrium is reached, forward and reverse reactions cancel, so no net changes are observed within the system. | 6. Argumentation |
| 7.2 Direction of Reversible Reactions | Learn to explain how the rates of forward and reverse reactions affect the net direction in which a reversible reaction occurs. | 4. Model Analysis |
| 7.3 Reaction Quotient and Equilibrium Constant | Learn to represent Qc or Qp of a reversible reaction and how these expressions relate to the equilibrium position Kc = Qc or Kp = Qp. | 3. Representing Data and Phenomena |
| 7.4 Calculating the Equilibrium Constant | Learn to calculate Kc or Kp based on the concentrations or pressures of chemical species at equilibrium. | 5. Mathematical Routines |
| 7.5 Magnitude of the Equilibrium Constant | Learn how the value of K relates to the ratio of products to reactants when at equilibrium. | 6. Argumentation |
| 7.6 Properties of the Equilibrium Constant | Learn how to represent a multistep process using an equilibrium expression and how the equilibrium constants of individual steps can be combined to give the overall equilibrium constant. | 5. Mathematical Routines |
| 7.7 Calculating Equilibrium Concentrations | Learn to use initial conditions, a balanced equation, and the appropriate K to identify the concentration or partial pressure of a species at equilibrium. | 3. Represent Data and Phenomena |
| 7.8 Representations of Equilibrium | Learn how to use particle diagrams to represent reversible reactions. | 3. Representing Data and Phenomena |
| 7.9 Introduction to Le Chȃtelier’s Principle | Learn how to use Le Chȃtelier’s principle to predict how a system will change in response to changes in external conditions. | 6. Argumentation |
| 7.10 Reaction Quotient and Le Chȃtelier’s Principle | Learn how to predict the direction of a reversible reaction by comparing Q and K. | 5. Mathematical Routines |
| 7.11 Introduction to Solubility Equilibria | Learn how to use a salt’s Ksp value to calculate its solubility. | 5. Mathematical Routines |
| 7.12 Common-Ion Effect | Learn how the solubility of a salt is affected by the presence of one of the ions in that salt, known as a common ion. | 2. Question and Method |
| 7.13 pH and Solubility | Learn to explain how the solubility of a salt is affected by changes in pH. | 2. Question and Method |
| 7.14 Free Energy of Dissolution | Learn to explain how dissolution of a salt changes the enthalpy and entropy of a system. | 4. Model Analysis |
To learn more about this unit, check out AP Chemistry Unit 7 – Equilibrium.
Acids and Bases
Exam Weight: 11–15%㇑Class Periods: 14–15
Acid-base reactions are reversible reactions in which protons are exchanged. Proton exchange is rapid, so acid-base reactions quickly reach equilibrium. These reactions tend to have either very small or very large values of the equilibrium constant K. In this unit, you will learn to use simple computations to draw conclusions about the equilibrium positions of acid-base reactions.
The big ideas explored in this unit are:
- Big Idea 2: Structure and Properties – How do acid-base reactions affect pH?
| Topics | Objective | Suggested Science Practice |
|---|---|---|
| 8.1 Introduction to Acids and Bases | Learn to use Kw and the concentrations of species found in an aqueous solution to calculate pH and pOH values. | 5. Mathematical Routines |
| 8.2 pH and pOH of Strong Acids and Bases | Learn to use the concentrations of species found in a strong acid-base solution to calculate pH and pOH. | 5. Mathematical Routines |
| 8.3 Weak Acid and Base Equilibria | Learn to explain how the concentrations of species in a monoprotic solution of a weak acid or a weak base are related to pH and pOH. | 5. Mathematical Routines |
| 8.4 Acid-Base Reactions and Buffers | Learn to explain how concentrations of major species are related in a mixture of weak and strong acids and bases. | 5. Mathematical Routines |
| 8.5 Acid-Base Titrations | Learn to explain how the results of a titration of monoprotic or polyprotic acid or base solutions are related to the properties of the solution. | 5. Mathematical Routines |
| 8.6 Molecular Structure of Acids and Bases | Learn to explain how the structure of a molecule or ion dictates the strength of an acid or base. | 6. Argumentation |
| 8.7 pH and pKa | Learn to explain how the pKa of a weak acid is related to the pKb of its conjugate base and vice versa, and how this relates to the predominant form of the acid or base at a particular pH. | 2. Question and Method |
| 8.8 Properties of Buffers | Learn to explain what a buffer is and how the reactions that occur when an acid or base is added to a buffered solution help stabilize the pH of the solution. | 6. Argumentation |
| 8.9 Henderson-Hasselbalch Equation | Learn how to calculate the pH of a buffer solution using the pKa of the acid and the concentration ratio of the conjugate acid-base pair. | 5. Mathematical Routines |
| 8.10 Buffer Capacity | Learn to explain how the buffer capacity of a solution is related to the concentrations of the conjugate acid and conjugate base in a buffer solution. | 6. Argumentation |
Looking for a more detailed study of this unit and its topics? Then read our guide on AP Chemistry Unit 8 – Acids and Bases.
Applications of Thermodynamics
Exam Weight: 7–9%㇑Class Periods: 10–13
The thermodynamics of a reaction depend on the structures of the reaction species and dictate the results of the reaction on a macroscopic scale. All chemical reactions involve energy. Chemical systems exchange energy with their environment during temperature changes, phase changes, and chemical reactions. Each of these processes often involve changes in electrostatic forces including interactions between molecules (intermolecular forces) and interactions within a molecule (chemical bonds). In this unit, you will learn to use the laws of thermodynamics to explain the role of energy in chemical reactions and predict the chemical and physical changes that occur under different conditions.
The big idea explored in this unit is:
- Big Idea 4: Energy – How is electric energy created during a chemical reaction and how is the possibility of a physical or chemical change determined?
| Topics | Objective | Suggested Science Practice |
|---|---|---|
| 9.1 Introduction to Entropy | Learn to identify the magnitude of an entropic change during a physical or chemical process. | 6. Argumentation |
| 9.2 Absolute Entropy and Entropy Change | Learn to use the absolute entropies of chemical species to calculate the entropy change in a physical or chemical process. | 5. Mathematical Routines |
| 9.3 Gibbs Free Energy and Thermodynamic Favorability | Learn to explain how the thermodynamic favorability of a process is related to ∆G°. | 6. Argumentation |
| 9.4 Thermodynamic and Kinetic Control | Learn to use kinetics to explain why a reaction that is thermodynamically favorable may not occur quickly. | 6. Argumentation |
| 9.5 Free Energy and Equilibrium | Learn how K, ∆G°, and T relate to the thermodynamic favorability of a reaction. | 6. Argumentation |
| 9.6 Coupled Reactions | Learn to explain how a thermodynamically unfavorable process can be driven by external sources of energy or by coupling to a favorable reaction. | 4. Model Analysis |
| 9.7 Galvanic (Voltaic) and Electrolytic Cells | Learn to explain how the operational principles of an electrochemical cell are related to the physical components that make up that cell. | 2. Question and Method |
| 9.8 Cell Potential and Free Energy | Learn to determine whether a reaction in an electrochemical cell is thermodynamically favorable by taking into account its standard cell potential and the half-reactions that take place within each cell. | 5. Mathematical Routines |
| 9.9 Cell Potential Under Nonstandard Conditions | Learn to explain how the observed potential of an electrochemical cell may differ from the standard potential due to changes in cell conditions. | 6. Argumentation |
| 9.10 Electrolysis and Faraday’s Law | Learn to use Faraday’s Law to calculate the rate of electron flow in an electrochemical cell based on the rate at which the reactants are consumed or the products are formed. | 5. Mathematical Routines |
To learn more about the topics in this unit, you can read our article AP Chemistry Unit 9 – Applications of Thermodynamics.
AP Chemistry Labs
Labs are an integral part of AP Chemistry, and they will help you better understand and apply the concepts that you are learning in class. At least 25% of your class time will be devoted to labs, and there are at least 16 different lab experiments to complete. These labs give you the skills to adopt an inquiry-based approach to studying chemistry, which will be highly useful when you get to college.
Listed below are some of the topics you will explore through the lab experiments you will perform in your AP Chemistry course:
- Redox Titration
- Solubility
- Acid-base Titration
- Buffers
- Stoichiometry
- Spectroscopy
To find out more about the lab experiments, what they will help you learn, and how they play a role in your final AP Chemistry exam, check out our article on AP Chemistry Labs.
Frequently Asked Questions
What is the hardest unit in AP Chemistry?
This is largely subjective as it depends on your aptitude for chemistry, your interest in the various units in the course, and the study materials and resources you use. However, taking into account the results of the 2021 exams, it was found that most students struggled with Unit 1, Unit 7, and Unit 8.
What are the most important topics for the AP Chemistry exam?
Based on the weighting of each unit in the exam, the most important units are Unit 8 – Acids and Bases and Unit 3 – Intermolecular Forces and Properties.
Read more about AP Chemistry
Do you want to know the best strategies and the finest resources to get the highest score in AP Chemistry? Check out our step-by-step AP Chemistry study guide to score a 5.
Looking for the AP Chemistry Exam format information? Find our article that clearly explains and breaks down the AP Chem Exam format, types of questions, sections, and more!