What is the enthalpy of the reaction as written?

Question

When 0.690 g of sodium metal is added to an excess of hydrochloric acid, 7170 J of heat are produced. What is the enthalpy of the reaction as written?

Answer 1

Convert g of Na to mol Na using its molar mass = 23 g/mol

0.690 g Na x (1 mol Na / 23 g Na) = 0.0300 mol

Since heat is produced, q = -7170 J

Enthalpy ΔH = q / mol = -7170 J / 0.0300 mol = -239,000 J/mol

If you want the answer in units of kJ/mol, then ΔH = -239,000 J/mol x (1 kJ / 1000 J) = -239 kJ/mol