⏱️ August 20, 2020
According to the College Board, "Unit 4 focused on chemical changes💥; in Unit 5 students will develop an understanding of the rates at which chemical changes occur and the factors that influence the rates📈. Those factors include the concentration of reactants, temperature, catalysts, and other environmental factors. Chemical changes are represented by chemical reactions, and the rates of chemical reactions are determined by the details of the molecular collisions.
Rates of change in chemical reactions are observable and measurable📏. When measuring rates of change, students are measuring the concentration of reactant or product species as a function of time. These chemical processes may be observed in a variety of ways and often involve changes in energy as well. In subsequent units, students will describe the role of energy⚡ in changes in matter."
Why are some reactions faster than other reactions?
How long will a marble statue last?🗿
How can a sports drink cure a headache?🤕
Why does bread rise?🍞
Kinetics is the study of the rate of chemical reactions, essentially how fast a chemical reaction goes💨. While we can study whether a reaction will actually happen or not using many tools, such as solubility rules and activity series, one cannot use these same tools to study the specific rate at which a reaction will happen. This is analogous to knowing whether someone moved or not since the last 5 seconds have passed, versus knowing with which speed they moved in that time interval.
✍️About 7-9% of the exam tests your knowledge from this unit.
To study the rates at which reactions take place, physical chemists (who study chemistry from a mathematical and physics-motivated perspective) model reactions using the collision model, which we will discuss shortly. This is the same theory used to model ideal gases.
The Collision Model of Kinetics - Image Courtesy of BCOpenTextbooks
Certain reactions are then categorized depending on a parameter n, which essentially describes how the amount of atoms in a sample (concentration) affects the rate of collisions (as a higher concentration --> more atoms = more collisions). This parameter n is called the reaction order. For example n = 1 is equivalent to first order, n = 2 is equivalent to second order, and the same pattern holds for higher values of n. We will come to learn of how reaction rate can be defined using a "rate law", essentially an equation that describes how changes in concentration impact the rate of a reaction (Sneak peek: R = k[A]^n)
The order of a reaction must either be determined experimentally, or through analyzing a reaction mechanism, which deeper describes the chemical details of a reaction. Instead of analyzing the reactions macroscopically, this method allows chemists to see a relatively more accurate picture regarding how and why a chemical reaction happens, instead of simply analyzing what products come from what reactants.
An energy diagram showing potential energy against reaction progress, a common way of showing activation energy, Image Courtesy of SoftSchools
These reaction mechanisms motivate finding overall rates, as the rates of each mechanistic step can be used to find the overall rate of the reaction by analyzing something called the rate-limiting step, which is conceptually similar to the concept of limiting reactants in stoichiometry.
✍️ Free Response Questions
AP Chemistry Free Response Questions
⚛️ Unit 1: Atomic Structure and Properties
1.1Moles and Molar Mass
1.2Mass Spectroscopy of Elements
1.3Elemental Composition of Pure Substances
1.4Composition of Mixtures
1.5Atomic Structure and Electron Configurations
1.6Photoelectron Spectroscopy & Graph Interp.
🤓 Unit 2: Molecular and Ionic Compound Structures and Properties
2.0Unit 2 Overview: Molecular and Ionic Bonding
2.1Types of Chemical Bonds
2.2Intramolecular Force and Potential Energy
2.3Ionic Bonding and Ionic Solids
2.4Metallic Bonding and Alloys
2.5Lewis Dot Diagrams
2.6Resonance and Formal Charge
🌀 Unit 3: Intermolecular Forces and Properties
3.0Unit 3 Overview: Intermolecular Forces and Properties
3.2Properties of Solids
3.3Solids, Liquids, and Gases
3.4The Ideal Gas Law
3.5The Kinetic Molecular Theory of Gases
3.6Deviations from the Ideal Gas Law
3.7Mixtures and Solutions
3.8Representations of Solutions
3.9Separation of Solids/Mixtures
3.10Solubility and Solubility Rules
3.11Spectroscopy and the Electromagnetic Spectrum
3.12Quantum Mechanics and the Photoelectric Effect
🧪 Unit 4: Chemical Reactions
4.0Unit 4 Overview: Chemical Reactions
4.1Recognizing Chemical Reactions
4.2Net Ionic Equations
4.4Physical vs. Chemical Changes
4.5Stoichiometry & Calculations
4.6Titrations - Intro and Calculations
4.8Intro to Acid-Base Neutralization Reactions
👟 Unit 5: Kinetics
5.0Unit 5 Overview: Kinetics
5.1Defining Rate of Reaction
5.2Introduction to Rate Laws
5.3Rate and Concentration Change
5.4Writing Rate Laws
5.5Collision Model of Kinetics
5.6Reaction Energy and Graphs w/ Energy
5.7Reaction Mechanisms and Elementary Steps
5.8Writing Rate Laws Using Mechanisms
🔥 Unit 6: Thermodynamics
6.0 Unit 6 Overview: Thermochemistry and Reaction Thermodynamics
6.1Endothermic Processes vs. Exothermic Processes
6.2Energy Diagrams of Reactions
6.3Kinetic Energy, Heat Transfer, and Thermal Equilibrium
6.4Heat Capacity and Coffee-Cup Calorimetry
6.5Phase Changes and Energy
6.6Introduction to Enthalpy of Reaction
6.7Bond Enthalpy and Bond Dissociation Energy
6.8Enthalpies of Formation
⚖️ Unit 7: Equilibrium
🍊 Unit 8: Acids and Bases
8.0Unit 8 Overview: Acids and Bases
8.1Introduction to Acids and Bases
Unit 9: Applications of Thermodynamics
🤺 AP Chemistry Essentials
🧐 Multiple Choice Questions
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