ThermochemistryHard

Question

The Δf Ho for CO2(g), CO(g) and H2O(g) are −393.5, −110.5 and −241.8 kJ mol–1, respectively. The standard enthalpy change (in kJ) for the reaction

CO2(g) + H2(g) → CO(g) + H2O(g) is

Options

A.524.1
B.41.2
C.–262.5
D.–41.2

Solution

$\Delta_{r}H^{o} = \sum_{}^{}{\Delta_{f}H_{\text{Products}}^{o} -}\sum_{}^{}{\Delta_{f}H_{\text{Reactants}}^{o}}$

$= \left\lbrack \Delta_{f}H_{CO(g)}^{o} + \Delta_{f}H_{H_{2}O(g)}^{o} \right\rbrack - \left\lbrack \Delta_{f}H_{CO_{2}(g)}^{o} + \Delta_{f}H_{H_{2}(g)}^{o} \right\rbrack $$$= \left\lbrack ( - 110.5) + ( - 241.8) \right\rbrack - \left\lbrack ( - 393.5) + 0 \right\rbrack = 41.2\text{ kJ}$$

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