Day 22 MCAT Practice Question

Passage 4: Hydrogen Peroxide

Hydrogen peroxide (H2O2) is a common component in fuels, antiseptics, and

bleaching agents due to its strong oxidizing properties. It decomposes into water

and O2 gas via the following relationship:

2H2O2 (aq) = 2H2O(l) + O2 (g) ΔH: -98kJ/mol (Reaction 1).

Researchers performed decomposition of H2O2 with potassium iodide (KI) at

various temperatures. Specifically, they measured the rate of oxygen gas evolution

at varying concentrations of H2O2 and KI as well as varying temperatures. Results

are summarized in Table 1:

The specific heat capacity of the hydrogen peroxide solution was measured to be

2.5 J/g°C and was slightly more dense than water at 1.45 g/cm3. Hydrogen peroxide

is quite environmentally friendly as an oxidizing agent because of this harmless

decomposition into water and oxygen gas.

At the end of the experiment, the researchers noticed that no potassium iodide

had been consumed over the course of their project, although its presence always

increased reaction rate relative to the same reaction run at the same temperature

and concentrations in its absence.

Given the provided data, what would be the effect on the rate of evolution of

oxygen gas when the concentration of hydrogen peroxide is quadrupled?

A) The rate would double

B) The rate would quadruple

C) The rate would be multiplied by a factor of sixteen

D) The rate would halve