Chapter 7: Chemical Kinetics

By the end of this chapter you will be able to:
  • Understand that chemical reactions that involve gases are good models for studying chemical reactivity due to limited intermolecular interactions:
    • Describe the behaviour of ideal and real gases using the kinetic molecular theory of gases.
  • Understand that the rate of any chemical reaction relates to the mechanism of the reaction:
    • Describe and apply the principles of collision theory to a given reaction.
    • Describe the factors affecting the collision frequency.
    • Use the Arrhenius equation to quantify the relationships between the activation energy, temperature and rate constant.
  • Understand that a reaction mechanism can be the result of one or several successive and effective collisions:
    • Propose and identify a valid mechanism for a given reaction.
    • Identify the rate-determining step, intermediates, transition states and catalysts present in a given reaction mechanism.
  • Understand that reaction coordinate diagrams provide a representation of the energy changes that influence rate:
    • Generate, interpret and relate a plausible reaction coordinate diagram to the proper reaction mechanism.
  • Understand that the rate law is used to quantitatively examine the rate of a reaction:
    • Determine and distinguish between average and instantaneous rates of reaction
    • Determine the differential and/or integrated rate laws for a given reaction, including the order and the rate constant for this reaction, using experimental data.
    • Generate and interpret graphs of concentration vs. time to compare rates and rate laws for different reactions.
  • Understand that the rate of a reaction can be altered by changing the conditions of a system:
    • Predict the change in the rate of reaction that results from changing reactant concentrations, temperature, or from the addition of a catalyst.
  • Understand that catalysts provide alternative mechanisms, thereby altering the energy changes and rates for a reaction:
    • Describe the effect of a catalyst on the mechanism of a reaction.
This image has an empty alt attribute; its file name is CNX_Chem_12_00_Ectotherm-1024x473.jpg
An agama lizard basks in the sun. As its body warms, the chemical reactions of its metabolism speed up.

The lizard in the photograph is not simply enjoying the sunshine – the heat from the sun’s rays is critical to the lizard’s survival. A warm lizard can move faster than a cold one, because the chemical reactions that allow its muscles to move proceed more quickly at higher temperatures. A cold lizard is a slow lizard and an easier meal for predators.

Chemical reactions are central to many applications, from baking a cake to choosing materials for a bridge. Chemists ask two questions when planning a chemical reaction: “Will the reaction make the right products, in the right amounts?” and “How fast will the reaction happen?”. Sometimes, a third question is asked: “What happens during the reaction?”

Chemical kinetics is the study of the second and third questions – considering how fast reactions happen and how they work at a molecular scale. In this chapter, you will learn about what affects reaction rates, how reactions work (“reaction mechanisms”), and how to measure reaction rates.

Sections in this chapter:

  1. Expressing Reaction Rates
  2. Factors Affecting Reaction Rates
  3. Rate Laws
  4. Integrated Rate Laws
  5. Collision Theory
  6. Reaction Mechanisms
  7. Catalysis