3.3: The Rate Law
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In studying a chemical reaction, it is important to consider not only the chemical properties of the reactants, but also the conditions under which the reaction occurs, the mechanism by which it takes place, the rate at which it occurs, and the equilibrium toward which it proceeds. According to the law of mass action, the rate of a chemical reaction at a constant temperature depends only on the concentrations of the substances that influence the rate. The substances that influence the rate of reaction are usually one or more of the reactants, but can occasionally include products. Catalysts, which do not appear in the balanced overall chemical equation, can also influence reaction rate. The rate law is experimentally determined and can be used to predict the relationship between the rate of a reaction and the concentrations of reactants.
- 3.3.1: Order of Reaction Experiments
- This is an introduction to some of the experimental methods used in school laboratories to find orders of reaction. There are two fundamentally different approaches to this: investigating what happens to the initial rate of the reaction as concentrations change, and following a particular reaction to completion and processing the results from that single reaction.
- 3.3.2: Rate Laws
- Reactions are often monitored by some form of spectroscopy. In spectroscopy, "light" or some other frequency of electromagnetic radiation passes through a reaction sample. The light interacts with the molecules in the sample, which absorb particular frequencies of light. Less light exits the sample than the amount that entered it; the amount that exits is measured by a detector on the other side.
- 3.3.3: Reaction Order
- The reaction order is the relationship between the concentrations of species and the rate of a reaction.