16: Chemical Kinetics I - Rate Laws
- Page ID
- 425054
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- 16.1: The Time Dependence of a Chemical Reaction is Described by a Rate Law
- The rate of a chemical reaction (or the reaction rate) can be defined by the time needed for a change in concentration to occur. But there is a problem in that this allows for the definition to be made based on concentration changes for either the reactants or the products. Plus, due to stoichiometric concerns, the rates at which the concentrations are generally different!
- 16.2: Rate Laws Must Be Determined Experimentally
- There are several methods that can be used to measure chemical reactions rates. A common method is to use spectrophotometry to monitor the concentration of a species that will absorb light. If it is possible, it is preferable to measure the appearance of a product rather than the disappearance of a reactant, due to the low background interference of the measurement.
- 16.3: First-Order Reactions Show an Exponential Decay of Reactant Concentration with Time
- If the reaction follows a first order rate law, it can be expressed in terms of the time-rate of change of [A]. The solution of the differential equation suggests that a plot of log concentration as a function of time will produce a straight line.
- 16.4: Different Rate Laws Predict Different Kinetics
- It is possible to determine the reaction order using data from a single experiment by plotting the concentration of the reactant as a function of time. Because of the characteristic shapes of such lines for zero-order, first-order, and second-order reactions, the graphs can be used to determine the reaction order of an unknown reaction.
- 16.5: Reactions can also be Reversible
- Many chemical reactions are reversible, in that the products formed during the process react to re-form the original reactants. These reversible reactions eventually reach a state of dynamic equilibrium, in which the rate of the overall forward process is equal to the rate of the overall reverse process.