The standard enthalpy change for the formation of 1 mole of carbon dioxide CO2 gas from solid elemental carbon C and gaseous molecular oxygen O2 at 298 K can be found using the standard enthalpy of formation values for the substances involved in the reaction.The standard enthalpy of formation Hf is the change in enthalpy when 1 mole of a substance is formed from its constituent elements in their standard states at 298 K and 1 atm pressure. For elemental carbon C and molecular oxygen O2 , the standard enthalpy of formation is zero because they are in their standard states.The standard enthalpy of formation for carbon dioxide CO2 gas is -393.5 kJ/mol.Using the balanced chemical equation: C s + O2 g CO2 g , we can calculate the standard enthalpy change for the reaction H using the following formula:H = [Hf products ] - [Hf reactants ]H = [1 mol -393.5 kJ/mol ] - [1 mol 0 kJ/mol + 1 mol 0 kJ/mol]H = -393.5 kJ/molTherefore, the standard enthalpy change for the formation of 1 mole of carbon dioxide CO2 gas from solid elemental carbon C and gaseous molecular oxygen O2 at 298 K is -393.5 kJ/mol.