Final answer:
The rate constant for the reaction is determined by the negative slope of the plot for a first-order reaction, which in this case is 0.287 s^{-1}.
Step-by-step explanation:
The rate constant for a chemical reaction can be determined from the slope of a linear plot on a graph showing the concentration of reactant over time. For a first-order reaction, this plot is of ln[A] versus time. According to the integrated rate law for first-order kinetics, which follows the equation -ln[A] = ln[A]0 - kt, a straight line with a slope of -k will be produced. Since the slope of the plot in the given experiment is -0.287, it directly corresponds to the rate constant 'k' for the reaction.