Question

The thermal effect of water formation reaction is 286 kJ. what will be the thermal effect of its decomposition. Why?

Answer 1

286 kJ

Step-by-step explanation:

• The heat change value in the forward reaction is equal to the heat change value in the reverse reaction.
• The only thing that changes is the sign on the heat value, such that if the forward reaction is endothermic then the reverse reaction is exothermic.

In this case;

• The enthalpy change of formation of water is -286 kJ/mol, this means that the reaction of formation of water is an exothermic reaction.
• The decomposition of water which is the reverse of formation has an enthalpy change of +286 kJ, the reaction is an endothermic reaction.
• Therefore, the thermal effect of decomposition of water has the same value as the the thermal effect of formation which is 286 kJ