When 0.705g of sodium metal is added to an excess of hydrochloric acid, 7330 J of heat are produced. What is the enthalpy of the reaction as written? 2Na(s)+2HCl(aq) ⟶2NaCl(aq)+H2(g)

Answer 1

Approach: The quantity of heat produced is related to number of moles of reactant on the balanced chemical equation. So, first find out how many moles of sodium are in 0.705 g of sodium (use molar mass of Na, which is nothing but the atomic mass of Na in g/mol). Then according to the balanced equation, you need to calculated how much heat will be released using 2 moles of Na.

Solution:

Moles of sodium =0.705g/23.0 g/mol = 0.031 mol

So if 0.031 mol Na releases 7330 J, then the 2 mol of Na would release....

[7330j/0.031] *[2 mol] = 4.73 x10⁵ J or 473 kJ