What is the enthalpy of the reaction as written?

Question

When 0.305g of sodium metal is added to an excess of hydrochloric acid,  3170J of heat are produced. What is the enthalpy of the reaction as written? (Hints: convert the heat given to kJ, and since heat is produced the reaction is exothermic, so make the heat negative. Note that the balanced equation contains 2 mol Na, so divide the heat by the moles of Na that reacted to get the per mole, and then finally multiply by 2.)

2Na(s)+2HCl(aq)⟶2NaCl(aq)+H2(g)

Answer 1

Enthalpy for a reaction is intensive (it is in kJ/mole of reaction) therefore, you need to calculate the top and the bottom separately and then do the division. Extensive variables depend on the amount of material involved: moles, mass, energy, time, volume, etc. and are proportional.

.305 g Na * (1mole/ 22.99 g Na) * (1 mole of rxn/2moles of Na) = moles of rxn

3170 J * (1 kJ/1000 J) = kJ released

Do the division to get kJ/mole rxn (Don't forget sign: exothermic)