Question

${Δ}_f{U}^{∘}$ of formation of $C{H}_4$ (g) at certain temperature is -393 kJ $mo{l}^{−1}$ . The value of ${Δ}_f{H}^{∘}$ is

• A. zero
• B. $<{Δ}_f{U}^{∘}$
• C. $>{Δ}_f{U}^{∘}$
• D. equal to ${Δ}_f{U}^{∘}$

Answer 1

Answer: (B)

$\underset{(s)}{C}+\underset{(g)}{2H_2}→\underset{(g)}{C{H}_4}$
$Δn_g=−1$
$ΔH=ΔU+Δn_{g}RT$
$Δn_g=−ve$
$ΔH<ΔU$