Using Standard Heats of Formation to Calculate ΔHº Calculate ΔHº in kilojoules for the synthesis of lime (CaO) from limestone (CaCO3), the key step in the manufacture of cement. CaCO3(s) → CaO(s) + CO2(g) ΔHºf[CaCO3(s)] = -1207.6 kJ/mol ΔHºf[CaO(s)] = -634.9 kJ/mol ΔHºf[CO2(g)] = -393.5 kJ/mol

Question

Using Standard Heats of Formation to Calculate ΔHº

Calculate ΔHº in kilojoules for the synthesis of lime (CaO) from limestone ([latex]CaCO_3[/latex]), the key step in the manufacture of cement.

[latex]CaCO_3[/latex](s) → CaO(s) + [latex]CO_2[/latex](g) [latex]ΔH^{º}_{f}[/latex][[latex]CaCO_3[/latex](s)] = -1207.6 kJ/mol

[latex]ΔH^{º}_{f}[/latex][CaO(s)] = -634.9 kJ/mol

[latex]ΔH^{º}_{f}[/latex][[latex]CO_2[/latex](g)] = -393.5 kJ/mol

STRATEGY

Subtract the heat of formation of the reactant from the sum of the heats of formation of the products.

Accepted Answer

[latex]\begin{aligned}\Delta H^{\circ} & =\left[\Delta H_{\mathrm{f}}^{\circ}(\mathrm{CaO})+\Delta H_{\mathrm{f}}^{\circ}\left(\mathrm{CO}_2 ight) ight]-\left[\Delta H_{\mathrm{f}}^{\circ}\left(\mathrm{CaCO}_3 ight) ight] \& =(1 \mathrm{~mol})(-634.9 \mathrm{~kJ} / \mathrm{mol})+(1 \mathrm{~mol})(-393.5 \mathrm{~kJ} / \mathrm{mol})-(1 \mathrm{~mol})(-1207.6 \mathrm{~kJ} / \mathrm{mol}) \& =+179.2 \mathrm{~kJ}\end{aligned}[/latex]

The reaction is endothermic by 179.2 kJ.

Question 8.8: Using Standard Heats of Formation to Calculate ΔHº Calculate......

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