Hydrogen peroxide decomposes to water and oxygen at constant pressure by the following reaction: 2H₂O₂ (l) → 2H₂O (l) + O₂ (g) △H = -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 (4.00 g) to moles:
n(H2O2) = mass/molar mass = 4.00 g / 34.0147 g/mol = 0.1176 mol

According to the balanced equation, 2 moles of H2O2 produce 196 kJ of heat energy, so 0.1176 mol of H2O2 produces:
q = -196 kJ/mol x 0.1176 mol = -23.1 kJ
Note that the negative sign indicates that this is an exothermic reaction (heat is released). Therefore, the best choice is B.

Hydrogen Peroxide Decomposes to Water and Oxygen at Constant Pressure