Three reactions and their enthalpy changes are given

CHEMISTRY · Single correct · A Level · Chemistry · Energetics · Energetics

Problem

Three reactions and their enthalpy changes are given. 1.

C(s) + O_{2}(g) \rightarrow CO_{2}(g) \qquad \Delta H_{1} = -394\,\text{kJ}

CO_{2}(g) + H_{2}(g) \rightarrow CO(g) + H_{2}O(g) \qquad \Delta H_{2} = +41\,\text{kJ}

A student combines equations 1 and 2---without further manipulation---to obtain the target equation

C(s) + \tfrac{1}{2}O_{2}(g) + H_{2}(g) \rightarrow CO(g) + H_{2}O(g)

and reports

\Delta H_{\text{target}} = -353\,\text{kJ}.

What is the correct value of

\Delta H_{\text{target}}

? (a)

-156\,\text{kJ}

(b)

+353\,\text{kJ}

(c)

-353\,\text{kJ}

(d)

+156\,\text{kJ}