Question

Hydrogen cyanide is a highly poisonous, volatile liquid. It can be prepared by the following reaction.
CH4(g) + NH3(g) → HCN(g) + 3 H2(g)
What is the heat of reaction at constant pressure? Use the following thermochemical equations.
N2(g) + 3 H2(g) → 2 NH3(g) ΔH = −91.8 kJ
C(graphite) + 2 H2(g) → CH4(g) ΔH = −74.9 kJ
H2(g) + 2 C(graphite) + N2(g) → 2 HCN(g) ΔH = 270.3 kJ

Answer 1

NH3(g)->N2(g)+3/2H2(G)=+45.9KJ(*1/2)and reversed
CH4(g)->C(graphite)+2H2(g)=+74.9KJ reversed
1/2H2(g)+C(graphite)+1/2N2(g)-> HCN(g)=+135.1KJ
Cancel out C(graphite)and 1/2N2(g) on opposite sides of the reaction.
NH3(g)->H2(g)+1/2H2(g)=+45.9KJ (simplified H2(g)with a factor of 3/2 to 1+1/2=3/2)
CH4(g)-> 2H2(s)=+74.9KJ
1/2H2(g)->HCN(g)=+135.1KJ
cancel out 1/2H2(g) and sum up the reations to obtain.
NH3(g)+CH4(g)->HCN+3H2(g)=+225.9KJ

Answer 2

103.6kJ

Answer 3

delta H= 45.9+74.9+135.15=255.95