Final answer:
Graphical methods determine the order of a reaction by plotting reactant concentration vs. time data. A linear plot of ln[reactant] indicates a first-order reaction, while a linear plot of 1/[reactant] indicates a second-order reaction. The slope allows for the estimation of the rate constant.
Step-by-step explanation:
Graphical Methods in Reaction Kinetics
To determine the reaction order using graphical methods, you plot concentration vs. time data for the reactant under consideration and analyze the shape and mathematical relationship of the resulting curve. A first-order reaction will yield a straight line when plotting the natural logarithm of reactant concentration (ln[A]) versus time. Conversely, a second-order reaction will yield a straight line when plotting the inverse of reactant concentration (1/[A]) versus time. The slope of these linear plots corresponds to the negative reaction rate constant (-k), permitting its calculation.
Applying this strategy to the provided reaction involving PH2-, you would create graphs of ln[PH2-] and 1/[PH2-] against time and look for linearity to deduce the reaction order. The magnitude of the slope in these graphs will help in estimating the rate constant for the reaction.