Calculate the heat released when 3.10 L of Cl2(g) with a density of 1.88 g/L reacts with an excess of sodium metal at 25°C and 1 atm to form sodium chloride

Answer 1

Write the equation and balance it.
Convert 3.10 L Cl2 to grams (using density), then to moles. Look up delta Hf for products and reactants, then
delta Hrxn = (delta Hproducts)-(delta Hreactants).

Answer 2

Then why am I calculating the moles if I just need to look up the Change in H for products and reactants...that isn't going to give me the heat released. What formulas do I need to use?