Question

When 3.0 grams of H2 is reacted with excess C at constant pressure, the reaction forms CH4 and releases 54.2 kJ of heat. C(s) + 2 H2(g) --> CH4(g) What is the enthalpy of the reaction in kJ/mol of CH4?

Answer 1

Q = -54.2 KJ

Molar mass of H2 = 2.016 g/mol


mass(H2)= 3.0 g

use:
number of mol of H2,
n = mass of H2/molar mass of H2
=(3 g)/(2.016 g/mol)
= 1.488 mol

So, when 1.488 mol of H2 reacts, Q = -54.2 KJ
for 2 mol of H2, Q = -54.2*2/1.488
= -72.8 KJ

Answer: -72.8 KJ