Question

When you add 0.330 g of sodium metal to an excess of hydrochloric acid, you find that 3430 J of heat are produced. What is the enthalpy of the reaction as written below?

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

Enthalpy of reaction:

Answer 1

Molar mass of Na = 23 g/mol

Given mass of Na added , m = 0.330 g

So number of moles of Na = mass/molar mass

                                      = 0.330 g / 23 (g/mol)

                                      = 0.0143 mol

The amount of heat liberated by the reaction of 0.0143 mol of Na is 3430 J

The balanced reaction is : 2Na(s) + 2HCl(aq) -------> 2NaCl(aq) + H₂ (g)

The amount of heat liberated by the reaction of 2 mol of Na is M J

M = ( 2x3430)/0.0143

    = 479.7x10³ J

    = 479.7 kJ

Therefore the enthalpy of the reaction = -479.7 kJ