The standard enthalpy changes of formation of carbon dioxide and water are -394 KJmol and -286 kJ mol respectively. If the standard enthalpy change of combustion of propyne, CH3CCH is -1938 KJ mol-1 , what is its standard enthalpy change of formation?

Explanation

Option C is correct.The standard enthalpy change of formation of propyne, CH3CCH is -184 kJ/mol. The standard enthalpy change of formation is the heat released when a compound is formed from its constituent elements in their standard states. The standard enthalpy change of combustion is the heat released when a compound is burned in oxygen. The standard enthalpy change of combustion of propyne can be written as follows: CH3CCH(g) + 5O2(g) → 3CO2(g) + 4H2O(g) The standard enthalpy change of combustion of propyne is -1938 kJ/mol. This means that 1938 kJ of heat is released when 1 mole of propyne is burned in oxygen. The standard enthalpy changes of formation of carbon dioxide and water can be written as follows: CO2(g) → C(g) + O2(g) ΔHf° = -394 kJ/mol H2O(g) → H2(g) + ½O2(g) ΔHf° = -286 kJ/mol The standard enthalpy change of formation of propyne can be calculated using the following equation: ΔHf°(CH3CCH) = ΔHcomb°(CH3CCH) - ΔHf°(CO2) - 4ΔHf°(H2O) Substituting the values from the previous equations, we get: ΔHf°(CH3CCH) = -1938 kJ/mol - (-394 kJ/mol) - 4(-286 kJ/mol) ΔHf°(CH3CCH) = -184 kJ/mol Therefore, the standard enthalpy change of formation of propyne is -184 kJ/mol.