Question

Use the following thermochemical equation to calculate how much heat in kilojoules is evolved or absorbed when 14.4g of liquid water are converted to hydrogen and oxygen gas. 

2H₂(g) + O₂(g) -----> 2H₂O (l)

Delat H°= -571.6 kJ

Answer 1

The given reaction is exothermic since delta H is negative.

But When liquid water reacts, the reaction is endothermic.

So, heat is absorbed.

Molar mass of H2O,

MM = 2*MM(H) + 1*MM(O)

= 2*1.008 + 1*16.0

= 18.016 g/mol

mass(H2O)= 14.4 g

use:

number of mol of H2O,

n = mass of H2O/molar mass of H2O

=(14.4 g)/(18.02 g/mol)

= 0.7993 mol

Since Δ H is positive, heat is absorbed

when 2 mol of H2O reacts, heat absorbed = 571.6 KJ

So,

for 0.7993 mol of H2O, heat absorbed = 0.7993*571.6/2 KJ

= 2.284*10^2 KJ

Answer: 228 KJ