For the decomposition reaction at standard conditions

CHEMISTRY · Single correct · AP · Chemistry · Thermochemistry · Thermochemistry

Problem

For the decomposition reaction CaCO3(s)→CaO(s)+CO2(g)\text{CaCO}_3(s)\rightarrow \text{CaO}(s)+\text{CO}_2(g) at standard conditions, which of the following expressions correctly relates the standard enthalpy change of reaction, ΔHrxn∘\Delta H^\circ_{\text{rxn}}, to standard enthalpies of formation, ΔHf∘\Delta H_f^\circ? (a) ΔHrxn∘=[ΔHf∘(CaCO3)+ΔHf∘(CaO)]−ΔHf∘(CO2)\Delta H^\circ_{\text{rxn}}=\bigl[\Delta H_f^\circ(\text{CaCO}_3)+\Delta H_f^\circ(\text{CaO})\bigr]-\Delta H_f^\circ(\text{CO}_2) (b) ΔHrxn∘=ΔHf∘(CaCO3)−[ΔHf∘(CaO)+ΔHf∘(CO2)]\Delta H^\circ_{\text{rxn}}=\Delta H_f^\circ(\text{CaCO}_3)-\bigl[\Delta H_f^\circ(\text{CaO})+\Delta H_f^\circ(\text{CO}_2)\bigr] (c) ΔHrxn∘=[ΔHf∘(CaO)+ΔHf∘(CO2)]−ΔHf∘(CaCO3)\Delta H^\circ_{\text{rxn}}=\bigl[\Delta H_f^\circ(\text{CaO})+\Delta H_f^\circ(\text{CO}_2)\bigr]-\Delta H_f^\circ(\text{CaCO}_3) (d) ΔHrxn∘=−ΔHf∘(CaCO3)\Delta H^\circ_{\text{rxn}}=-\Delta H_f^\circ(\text{CaCO}_3)

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