Hydrogen peroxide decomposes to water and oxygen at constant pressure by the following reaction: 2H₂O₂(l) → 2H₂O(l) + O₂(g) Δ_rH = -196 kJ
Calculate the value of q (kJ) in this exothermic reaction when 4.00 g of hydrogen peroxide decomposes at constant pressure?

Question

Quizplus · Accepted Answer

First, we need to convert the given mass of hydrogen peroxide to moles:

4.00 g H2O2 x (1 mol H2O2 / 34.0147 g H2O2) = 0.1176 mol H2O2

Using the balanced equation, we can see that the reaction produces 196 kJ of heat per 2 moles of H2O2 decomposed:

-196 kJ / 2 mol H2O2 = -98 kJ/mol H2O2

Multiplying by the number of moles we have and adding the negative sign to indicate that the reaction is exothermic, we get:

q = -(0.1176 mol H2O2)(98 kJ/mol H2O2) = -11.5 kJ

Therefore, the answer is B, -11.5 kJ mol-1.

Hydrogen Peroxide Decomposes to Water and Oxygen at Constant Pressure