Question

Calculate the standard enthalpy change for the combustion reaction of octane (C8H18) using the following balanced chemical equation:C8H18 + 12.5O2 →8CO2 + 9H2O Given the standard enthalpies of formation for CO2, H2O, and octane are -394 kJ/mol, -286 kJ/mol, and -249 kJ/mol respectively.

Answer 1

To calculate the standard enthalpy change for the combustion reaction of octane, we can use the following formula:H_combustion =  Hf_products -  Hf_reactantswhere H_combustion is the standard enthalpy change for the combustion reaction, Hf_products are the standard enthalpies of formation for the products, and Hf_reactants are the standard enthalpies of formation for the reactants.First, let's find the total enthalpy of formation for the products:8 mol CO2 *  -394 kJ/mol CO2  + 9 mol H2O *  -286 kJ/mol H2O  = -3152 kJ +  -2574 kJ  = -5726 kJNow, let's find the total enthalpy of formation for the reactants:1 mol C8H18 *  -249 kJ/mol C8H18  + 12.5 mol O2 * 0 kJ/mol O2 = -249 kJ + 0 kJ = -249 kJ Note that the standard enthalpy of formation for O2 is 0 kJ/mol because it is in its standard state. Now, we can calculate the standard enthalpy change for the combustion reaction:H_combustion = -5726 kJ -  -249 kJ  = -5726 kJ + 249 kJ = -5477 kJSo, the standard enthalpy change for the combustion reaction of octane is -5477 kJ.