Chemistry 2003 JAMB Past Questions - Question 28: CO(g)+ H2O(g) → CO2(g) + H2O From the reaction above, calculate the standard heat change if the standard enthalpies of formation of CO2(g),  H2O, and CO(g) in kJ mol-¹ are -394, 242 and -110 respectively.

Correct Answer

B

Explanation

 To calculate the standard heat change for the given reaction, we can use the standard enthalpies of formation of the reactants and products. The standard heat change (\(ΔH^\circ\)) for the reaction can be calculated using the formula:

\[ΔH^\circ = ΣnΔH_f^\circ(\text{products}) - ΣmΔH_f^\circ(\text{reactants})\]

Where \(n\) and \(m\) are the stoichiometric coefficients of the products and reactants, and \(ΔH_f^\circ\) is the standard enthalpy of formation.

For the given reaction:
\[CO + Hâ‚‚O(g) → COâ‚‚(g) + Hâ‚‚O\]

The standard heat change can be calculated as follows:

\[ΔH^\circ = [1 * (-394) + 1 * (242)] - [1 * (-110) + 1 * 0]\]
\[ΔH^\circ = (-394 + 242) - (-110) = -152 - (-110) = -152 + 110 = -42 kJ mol^{-1}\]

Therefore, the standard heat change for the given reaction is -42 kJ molâ�»¹.