if my reaction is 2Na + 2H2O -> 2NaOH +H2, and i have been given 1 gram of sodium, how would i measure the theoretical change in heat of the reaction, assuming the reactants are at room temperature?
Look in your text, probably in the appendix, for delta H0 tables. Those usually are given at 25 degrees C and that is about room temperature.
Heat of rxn = deltaH products - deltaH reactants. The numbers in the appendix are per mol (or kJ/mol), usually; therefore, multipy what you find for NaOH by 2 and what you find for water by 2, etc. Na and H2 will be zero.