(61) Heat of Reaction - LearnChemE.com

1. In the steam reforming of C2H4, steam reacts with C2H4 to produce CO and H2. Th heat of reaction is +200 kJ per mole of C2H4. If water were used as a liquid instead of a vapor, the heat reaction would . . . . . . . . . . .

• remain the same
• increase
• decrease
• be a negligible change

SOLUTION :

BEFORE

C2H4(g) + 2H2O(g) ==> 2CO (g) + 4H2(g)

Heat of Reaction = + 200 kJ/mole of C2H4 . . . . . . (1)

AFTER

There are two reaction equations

First, water in liquid phase is changed to gas phase (steam). It requires energy/heat.

After that, the steam is reacted with C2H4.

It can be stated as below.

H20(l) ===> H2O(g)

Heat of Reaction = +x kJ/mole of H2O

2H20(l) ===> 2H2O(g)

Heat of Reaction = +2x kJ . . . . . . . . (2)

C2H4(g) + 2H2O(g) ====> 2CO (g) + 4H2(g)

Heat of Reaction = +200 kJ/mole of C2H4

C2H4(g) + 2H2O(g) ====> 2CO (g) + 4H2(g)

Heat of Reaction = +200 kJ . . . . . . . . (3)

Reaction no. 2 plus Recation no.3 gives :

C2H4(g) + 2H2O(l) ====> 2CO (g) + 4H2(g)

Heat of Reaction = (200 + 2x) kJ . . . . . . . . (4)

It means the heat reaction would increase.

Note :

l = liquid

g = gas