When 0.467 g of sodium metal is added to an excess of hydrochloric acid, 4850 J of heat are produced. What is the enthalpy of the reaction as written?

Question

When 0.467 g of sodium metal is added to an excess of hydrochloric acid, 4850J of heat are produced. What is the enthalpy of the reaction as written?

2Na(s)+2HCl(aq)⟶2NaCl(aq)+H2(g)

Enthalpy of reaction:____________kj

Answer 1

Write the correctly balanced equation:

2Na(s) + 2HCl(aq) ==> 2NaCl(aq) + H2(g) + 4850 J ... balanced equation

Note that the 4850 J of heat appear as a product since heat is being produced. This is the heat produced when 0.467 g of Na reacts with excess HCl. For the balanced reaction as written, we need to find the heat produced from TWO moles ol Na.

atomic mass Na = 22.99g / mole

moles Na used = 0.467 g x 1 mol / 22.99 g = 0.02023 moles Na

To find the heat from 2 moles of Na, we proceed as follows:

2 moles Na x 4850 J / 0.02023 mols Na = 479,486 J = 479 kJ (3 sig. figs.)