Question

Calculate the enthalpy change of combustion for ethane (C2H6) given that the standard enthalpy of formation for ethane is -84.68 kJ/mol, the standard enthalpy of formation for CO2 is -393.5 kJ/mol, and the standard enthalpy of formation for H2O is -241.8 kJ/mol.

Answer 1

To calculate the enthalpy change of combustion for ethane, we first need to write the balanced chemical equation for the combustion reaction:C2H6 + O2  2CO2 + 3H2ONow, we can use Hess's Law, which states that the enthalpy change of a reaction is the sum of the enthalpy changes of formation of the products minus the sum of the enthalpy changes of formation of the reactants.H_combustion = [H_f products ] - [H_f reactants ]For the products, we have 2 moles of CO2 and 3 moles of H2O:H_f products  =  2  -393.5 kJ/mol  +  3  -241.8 kJ/mol  = -787 kJ/mol +  -725.4 kJ/mol  = -1512.4 kJ/molFor the reactants, we have 1 mole of ethane and the enthalpy of formation for O2 is zero since it is an element in its standard state:H_f reactants  =  -84.68 kJ/mol  + 0 = -84.68 kJ/molNow, we can calculate the enthalpy change of combustion:H_combustion =  -1512.4 kJ/mol  -  -84.68 kJ/mol  = -1427.72 kJ/molTherefore, the enthalpy change of combustion for ethane  C2H6  is -1427.72 kJ/mol.