. Using your calculated value for molar heat of reaction, how much heat would be given off in kilojoules if 3.0 grams of magnesium were to react with excess hydrochloric acid. Show work for your calculation.

Value is 31.304 kJ/mol Mg

So you have 31.304 kJ/mol.

How many mols are in 3.0 g Mg? That's mols = grams/molar mass = ?
Then 31.304 kJ/mol Mg x ? mols Mg = ? kJ heat given off.