homework question

Question

When 0.672  g of sodium metal is added to an excess of hydrochloric acid,  6990 J of heat are produced.

What is the enthalpy (in kj) of the reaction as written?

 

2 Na (s) + 2 HCl (aq) ⟶ 2 NaCl (aq) + H2 (g)

Answer 1

atomic mass Na = 22.99 g/mole

0.672 g Na x 1 mol Na / 22.99 g = 0.0292 moles Na

∆H = 6990 J/0.0292 moles = 239,383 J/mole = 239.4 kJ/mol Na

2Na(s) + 2HCl ==> 2NaCl(aq) + H2(g)

This reaction has 2 moles of Na being used. The enthalpy for this reaction would thus be...

2 mol Na x 239.4 kJ/mol = 478.8 kJ