A chemist measures the energy change? H during the following reaction:

2H2O (l) ?2H2 (g) + O2 (g)

=? H572. kJ

Is the reaction endothermic or exothermic?

Does it absorb or release heat when 75.8 of H2O react?

Using the numbers above how many kJ of heat will be released or absorbed?

Endothermic

It absorbs heat

1.20 * 10³ kJ

Explanation:

Let's consider the following thermochemical equation.

2 H₂O (l) → 2 H₂ (g) + O₂ (g) ΔH = 572 kJ

Since ΔH > 0, the reaction is endothermic, that is, it absorbs heat when H₂O reacts.

572 kJ are absorbed when 36.03 g of water react. The heat absorbed when 75.8 g of H₂O react is:

75.8 g H₂O * (572 kJ/36.03 g H₂O) = 1.20 * 10³ kJ