Question

Describe at least two experiments you could perform to determine a rate law.

Short answer

To determine a rate law, two experiments can be performed: Experiment 1 - Method of Initial Rates, and Experiment 2 - Integrated Rate Law Method. In the first experiment, varying initial concentrations of reactants are used, and initial reaction rates are measured. Plotting the initial rates against initial concentrations helps determine the reaction order and rate constant. In the second experiment, concentrations of reactants or products are measured over time and fitted to an integrated rate law equation, resulting in the order of the reaction and rate constant.

Step-by-step solution

Experiment 1: Method of Initial Rates

The method of initial rates involves performing a series of experiments in which the initial concentrations of reactants are varied and the initial rate of the reaction is measured. To do this experiment, follow these steps: 1. Set up the reaction with varying initial concentrations of the reactants and keep all other factors (e.g. temperature, pressure) constant. 2. Measure the initial rate of the reaction for each experiment. 3. Analyze the data by plotting the initial rate versus the initial concentration of one reactant while keeping the other reactant's concentration constant. 4. Determine the order of the reaction for each reactant by finding the slope of the curve in the plotted graph (i.e., the exponent of concentration in the rate law). 5. Obtain the rate constant by fitting the data to the rate law equation.

Experiment 2: Integrated Rate Law Method

The integrated rate law method involves measuring the concentration of reactants or products over time and fitting this data to an integrated rate law equation. Depending on the type of reaction (zero, first or second order), different equations will be used to fit the data. To carry out this experiment, follow these steps: 1. Set up the reaction under constant conditions (temperature, pressure) and with initial concentrations of the reactants. 2. Measure the concentration of a reactant or product over time intervals. 3. Plot the concentration data versus time. The shape of the plot will indicate the order of the reaction (linear for zero and first order, parabolic for second order). 4. Fit the data to the appropriate integrated rate law equation (depending on the order of the reaction) to determine the reaction order and rate constant. After completing both experiments, we will have determined the rate law for the given chemical reaction, including the reaction order and rate constant.