A chemist investigates the decomposition of compound X in aqueous solution at 25 °C. Three separate plots of the experimental data are summarized verbally below.
• Plot I: concentration of X, [X] (mol L⁻¹), versus time (s) shows a smooth downward curve that becomes less steep with time.
• Plot II: natural logarithm of the concentration, ln[X], versus time (s) appears as a straight line that slopes downward.
• Plot III: reciprocal concentration, 1/[X] (L mol⁻¹), versus time (s) shows a smooth upward curve that becomes more steep with time.
Answer the following questions about the reaction kinetics of compound X.
(1) Identify which one of the three plots (I, II, or III) provides the most direct evidence for a constant rate constant during the experiment and explain your reasoning.
(2) Based on your answer to part (a), state the overall reaction order with respect to X and justify the conclusion in terms of the mathematical form of the integrated rate law.
(3) From the appearance of the chosen plot, the linear fit has an equation of the form y=−0.0048x+1.85, where y represents the plotted quantity and x is the time in seconds. Determine the numerical value and SI units of the rate constant for the decomposition of X, and indicate whether the sign of the slope is consistent with the physical meaning of the rate constant.