Hydrogen peroxide decomposes to water and oxygen at constant pressure by the following reaction:
(l)→ O(l)+ (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

Hydrogen peroxide decomposes to water and oxygen at constant pressure by the following reaction: 
  (l)→  O(l)+  (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?

Quizplus · Accepted Answer

First, we need to determine the number of moles of hydrogen peroxide present:

moles H2O2 = mass/molar mass
moles H2O2 = 4.00 g / 34.0147 g/mol
moles H2O2 = 0.1176 mol

From the balanced chemical equation, we can see that the reaction produces 1 mole of O2 and releases 196 kJ of heat. Therefore, the amount of heat released in this reaction can be calculated as:

q = -196 kJ/mol × 0.1176 mol
q = -23.1 kJ

Since the reaction is exothermic, q has a negative value. Therefore, the best choice is B, which is the only option with a negative value for q.

Hydrogen Peroxide Decomposes to Water and Oxygen at Constant Pressure