Q6 of 62 Page 68

Δfof formation of CH4 (g) at certain temperature is –393 kJ mol–1. The value of Δf is

Reason: C (s) + 2H2 (g) → CH4 (g)

Δf = Δf + ΔngRT


Δng= 1-2= -1


Substituting the value of Δng, above equation will become


Δf = Δf- RT


As temperature and gas constant both have a positive value, so the value of Δf will become more negative.

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