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Enthalpy

Which one of ...

Question

Which one of the following statement(s) is/are true?

A

Δ E = 0

for combustion of

C_{2} H_{6} (g)

in a sealed rigid adiabatic container

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B

Δ_{f} H^{o} (S, m o n o l i t h i c) \neq 0

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C

If dissociation energy of

C H_{4} (g)

is

1656 k J / m o l

and

C_{2} H_{6} (g)

is

2812 k J / m o l

, then value of

C - C

bond energy will be

328 k J / m o l

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D

If

{Δ H}_{f} (H_{2} O, g) = - 242 k J / m o l; {Δ H}_{v a p} (H_{2} O, l) = 44 k J / m o l

then

Δ_{f} H^{o} ({O H}^{-}, a q)

will be

- 142 k J / m o l

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Solution

The correct options are
A $Δ_{f} H^{o} (S, m o n o l i t h i c) \neq 0$
B $Δ E = 0$ for combustion of $C_{2} H_{6} (g)$ in a sealed rigid adiabatic container
C If dissociation energy of $C H_{4} (g)$ is $1656 k J / m o l$ and $C_{2} H_{6} (g)$ is $2812 k J / m o l$ , then value of $C - C$ bond energy will be $328 k J / m o l$
$Δ_{f} H^{o} (S, m o n o l i t h i c) \neq 0$ as it is not elemental form of S.
$Δ E = 0$ for combustion of $C_{2} H_{6} (g)$ in a sealed rigid adiabatic container as in adiabatic process energy exchange is zero.
For $C_{2} H_{6} (g)$ ,
$B E_{C - C} = 2812 - 6 \times B E_{C - H} = 2812 - 6 \times 1656 / 4 = 328$ kJ/mol

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