Chemistry

Chemistry

Problem

When magnesium carbonate is heated, it decomposes according to MgCO3(s)⟶MgO(s)+CO2(g)\text{MgCO}_3(s)\longrightarrow \text{MgO}(s)+\text{CO}_2(g) Use the following thermochemical equations, all measured at 298 K298\,\text{K}: 1. Mg(s)+12 O2(g)⟶MgO(s)ΔH1∘=−602 kJ mol−1\text{Mg}(s)+\tfrac{1}{2}\,\text{O}_2(g)\longrightarrow \text{MgO}(s)\qquad \Delta H_1^{\circ}=-602\,\text{kJ}\,\text{mol}^{-1} 2. C(s)+O2(g)⟶CO2(g)ΔH2∘=−394 kJ mol−1\text{C}(s)+\text{O}_2(g)\longrightarrow \text{CO}_2(g)\qquad \Delta H_2^{\circ}=-394\,\text{kJ}\,\text{mol}^{-1} 3. Mg(s)+C(s)+32 O2(g)⟶MgCO3(s)ΔH3∘=−1096 kJ mol−1\text{Mg}(s)+\text{C}(s)+\tfrac{3}{2}\,\text{O}_2(g)\longrightarrow \text{MgCO}_3(s)\qquad \Delta H_3^{\circ}=-1096\,\text{kJ}\,\text{mol}^{-1} (a) Determine the standard molar enthalpy change for the thermal decomposition of magnesium carbonate shown above. (b) Calculate the enthalpy change per gram of MgCO3\text{MgCO}_3 decomposed. Report your answer in kJ g−1\text{kJ}\,\text{g}^{-1} to three significant figures. (c) A laboratory procedure decomposes 25.0 g25.0\,\text{g} of MgCO3\text{MgCO}_3. Compute the quantity of heat that must be supplied, assuming the process occurs at constant pressure and the measured enthalpy change equals the value from part (a).

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