Calculate the heat of a reaction Say I would like to calculate the heat produced by the following reaction:

$$\ce{2SO2 + O2\longrightarrow2SO3}$$

I have calculated the moles of the reagents. I can't seem to figure out how to calculate the heat of the reaction.

How can I calculate the heat of a reaction with moles of reagents?
in order to calculate the heat of reaction, you need the bond energies (which are measured in $\mathrm{kJ/mol}$ and usually provided in the question or in an appendix in the back of the chemistry book). The heat of reaction is equal to the energy of bonds broken minus the energy of the bonds created. It would be equal:

$[4*(\ce{S-O} $ bond energy$) ~+ ~1*(\ce{O=O} $ bond energy$)] - [6*(\ce{S-O} $ bond energy$)]$.

This will give a negative answer if the reaction is exothermic and vice versa. Since it is measured in $\mathrm{kJ/mol}$, multiply by moles to get the total energy released.