Q:

How Do You Calculate Heat of Reaction?

A:

The heat of reaction or the enthalpy of the reaction is the measure of change in enthalpy and can be determined both experimentally and numerically. In order to numerically determine the heat of reaction, the heat of formation values for the products and reactants must be known and applied to the equation: H = sum((v_p * H_p)) - sum((v_r * H_r)). H is the heat of reaction, v_p is the stoichiometric coefficient of the products, H_p is the heat of formation of the products, v_r is the stoichiometric coefficient of the reactant and H_r is the heat of formation of the reactant.

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1. Balance the given chemical equation

If given the chemical formula for the combustion of cellulose, C6H10O5 + O2 -> CO2 + H2O, it would be balanced as C6H10O5 + 6(O2) -> 6(CO2) + 5(H2O).

2. Find the heat of formation for the species of the reaction

The heat of formation is an experimentally determined value and is found in the back of many science textbooks and online. For cellulose, the heat of formation is -1250 kJ/mol, O2 is 0 kJ/mol, CO2 is -393.5 kJ/mol and H2O is -241.8 kJ/mol.

3. Calculate the equation for the heat of reaction

Putting the coefficients and heat of formation values together, the equation is: H = ((6 * -393.5) + (5 * -241.8)) - (-1250). Therefore, the heat of reaction is -2320 kJ/mol.