Questions: Calculating the heat of reaction from molar reaction enthalpy and the mass... A chemist measures the energy change ΔH during the following reaction: 2 H2O(l) → 2 H2(g) + O2(g) ΔH=572 kJ This reaction is... 0 endothermic. exothermic. Suppose 50.4 g of H2O react. Will any heat be released or absorbed? - Yes, absorbed. Yes, released. No. If you said heat will be released or absorbed in the second part of this question, calculate how much heat will be released or absorbed. Be sure your answer has the correct number of significant digits. kJ

Solution Steps

The given reaction is: \[ 2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow 2 \mathrm{H}_{2}(g) + \mathrm{O}_{2}(g) \quad \Delta H = 572 \, \mathrm{kJ} \] Since the enthalpy change \(\Delta H\) is positive, the reaction absorbs energy from the surroundings. Therefore, the reaction is endothermic.

Given that the reaction is endothermic, heat will be absorbed when the reaction occurs. Therefore, if 50.4 g of \(\mathrm{H}_{2} \mathrm{O}\) react, heat will be absorbed.

1. Calculate the moles of \(\mathrm{H}_{2} \mathrm{O}\):

   • Molar mass of \(\mathrm{H}_{2} \mathrm{O}\) is approximately \(18.015 \, \mathrm{g/mol}\).
   • Moles of \(\mathrm{H}_{2} \mathrm{O}\) = \(\frac{50.4 \, \mathrm{g}}{18.015 \, \mathrm{g/mol}} \approx 2.797 \, \mathrm{mol}\).

2. Calculate the heat absorbed:

   • The reaction given is for 2 moles of \(\mathrm{H}_{2} \mathrm{O}\) with \(\Delta H = 572 \, \mathrm{kJ}\).
   • Heat absorbed per mole of \(\mathrm{H}_{2} \mathrm{O}\) = \(\frac{572 \, \mathrm{kJ}}{2 \, \mathrm{mol}} = 286 \, \mathrm{kJ/mol}\).
   • Total heat absorbed = \(2.797 \, \mathrm{mol} \times 286 \, \mathrm{kJ/mol} \approx 800.042 \, \mathrm{kJ}\).

Final Answer