Question 13
Given
N2(g) + 3H2(g) → 2NH3(g) ; ΔrH0 = –92.4 kJ mol–1
What is the standard enthalpy of formation of NH3 gas?
Standard enthalpy of formation of a compound is the change in enthalpy that takes place during the formation of 1 mole of a substance in its standard form from its constituent elements in their standard state.
Re-writing the given equation for 1 mole of NH3(g),
½ N2(g) + 3/2 H2(g) → NH3(g)
= ½ ΔrHθ
= ½ (-92.4 kJ mol-1)
= - 46.2 kJ mol-1
