Given the following standard heats of reactions:
(a) heat of formation of water `= -68.3 kcal`, (b) heat of combustion of `C_(2)H_(2) =- 310.6 kcal`, (c ) heat of combustion of ethylene `=- 337.2 kcal`. Calculate the heat of reaction for the hydrogenation of acetylene at constant volume and at `25^(@)C`.

Explanation

To calculate the heat of reaction for the hydrogenation of acetylene (C₂H₂) at constant volume and at 25°C, we can use the given heats of formation and combustion. The reaction we are interested in is:

\[ \text{C}_2\text{H}_2 + \text{H}_2 \rightarrow \text{C}_2\text{H}_4 \]

### Step 1: Write the relevant reactions and their enthalpy changes

1. **Heat of formation of water**:
\[
...