Hydrogen peroxide decomposes to form oxygen gas and liquid water. In biological systems this reaction is often catalyzed by the enzyme catalase.
2 H₂O₂(aq) → 2 H₂O(l) + O₂(g)
A researcher studies the catalyzed reaction at two temperatures while keeping all other experimental variables constant. The initial rates are measured as shown below.
Temperature (°C) | Initial Rate (mol L⁻¹ s⁻¹)
5 | 1.2 × 10⁻⁵
45 | 4.8 × 10⁻⁴
At temperatures above 55 °C, the observed rate of the catalyzed reaction begins to decrease sharply even though the uncatalyzed reaction rate continues to increase.
(a) Using the data in the table, calculate the factor by which the catalyzed reaction rate increases when the temperature is raised from 5 °C to 45 °C.
(b) Provide a molecular-level explanation for the rate increase observed between 5 °C and 45 °C.
(c) Propose a reason, rooted in the properties of the catalyst, for why the catalyzed reaction rate decreases at temperatures above 55 °C even though higher temperatures generally speed chemical reactions.
(d) The researcher repeats the experiment at 5 °C using a synthetic (non-protein) catalyst that does not denature. Predict whether the rate–temperature relationship for this new catalyst is likely to follow the same trend observed for the uncatalyzed reaction at temperatures up to 80 °C, and justify your prediction.