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Standard XII

Chemistry

Gibbs Free Energy & Spontaneity

Δ H and Δ S...

Question

$Δ H$ and $Δ S$ for the system
$H_{2} O (l) ⇌ H_{2} O (g)$
at $1$ atmospheric pressure are $40.63 k J {m o l}^{- 1}$ and $108.8 J K^{- 1} {m o l}^{- 1}$ respectively. Calculate the temperature at which the rates of forward and backward reactions will be the same. Predict the sign of free energy for this transformation above this temperature.

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Solution

Given, $Δ H = 40.63 k J {m o l}^{- 1}$
$Δ S = 108.8 J K^{- 1} {m o l}^{- 1} = 0.1088 k J K^{- 1} {m o l}^{- 1}$
$Δ G = 0$ (when the system is in equilibrium)
Applying $Δ G = Δ H - T Δ S$
The sign of $Δ G$ above $373 K$ , say $374 K$ may be calculated as follows
Again applying $Δ G = Δ H - T Δ S$
$40.63 - 374 \times 0.1088$
$= - 0.06 k J$
$Δ G$ will be negative; hence the reaction will be spontaneous.

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Similar questions

△ H

and

△ S

for the equilibrium reaction,

H_{2} O (l) ⇌ H_{2} O (g)

at 1 atmospheric pressure are

40.63 k J m o l^{- 1}

and

108.8 J K^{- 1} m o l^{- 1}

respectively. Calculate the temperature at which the reaction occur.
Also, predict the sign of free energy for this transformation above this temperature.

△ H

and

△ S

for the equilibrium reaction,

H_{2} O (l) ⇌ H_{2} O (g)

at 1 atmospheric pressure are

40.63 k J m o l^{- 1}

and

108.8 J K^{- 1} m o l^{- 1}

respectively. Calculate the temperature at which the reaction occur.
Also, predict the sign of free energy for this transformation above this temperature.

Δ H

and

Δ S

for the reaction,

{A g}_{2} O (s) ⟶ 2 A g (s) + \frac{1}{2} O_{2} (g)

are

30.56 k J {m o l}^{- 1}

and

66.0 J K^{- 1} {m o l}^{- 1}

respectively. Calculate the temperature at which free energy change for the reaction will be zero. Predict whether the forward reaction will be forward above or below this temperature.

The $Δ H$ and $Δ S$ for a reaction at one atmospheric pressure are +30.558 kJ and 0.066 k J $k^{- 1}$ respectively. The temperature at which the free energy change will be zero and below this temperature the nature of reaction would be:

Q. For the reaction,

{A g}_{2} O ⇌ 2 A g (s) + \frac{1}{2} O_{2} (g)

Calculate the temperature at which free energy change is zero. At a temperature lower than this, predict whether the forward of the reverse reaction will be forward. Give reason
(

Δ H = + 30.56 k J; Δ S == + 0.066 k J K^{- 1} {m o l}^{- 1}

)

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