A student monitors the decomposition of aqueous hydrogen peroxide, 2 H2O2(aq) → 2 H2O(l) + O2(g), at 298 K. The student records the concentration of H2O2 every 10 s and constructs a smooth concentration-versus-time curve that is concave upward and decreasing throughout the 120-s experiment.
Answer the following questions about the graphical representation of the data.
(a) Describe, in terms of graphical features, how the instantaneous rate of decomposition of H2O2 at t = 40 s is obtained from the concentration-versus-time curve.
(b) Explain why the instantaneous rate determined in part (a) is negative when expressed as d[H2O2]/dt and how chemists conventionally report the rate so that it is a positive quantity.
(c) The slope of the tangent at t = 40 s is numerically equal to −3.2 × 10−5 M s−1. Explain how this value relates to the rate of production of O2(g) at the same instant, including appropriate stoichiometric reasoning.