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Standard XII

Chemistry

Gibbs Free Energy & Spontaneity

When CaCO3 ...

Question

When $C a C O_{3}$ is heated to a high temperature, it undergoes decomposition into $C a C O$ and $C O_{2}$
whereas it is quite stable at room temperature. The most likely explanation of it is:

The enthalpy of reaction

(Δ H)

overweight the term

T Δ S

at high temperature

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The term

T Δ S

overweight the enthalpy of reaction at high temperature

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At high temperature, both enthalpy of reaction and entropy change become negative.

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None of these

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Solution

The correct option is A The term $T Δ S$ overweight the enthalpy of reaction at high temperature
$Δ G = Δ H - T Δ S$
At high temperature $T Δ S$ factor dominates of $Δ H$ and hence $Δ G$ becomes negative and reaction occurs spontaneously.

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Similar questions

Gibbs-Helmholtz equation relates the free energy change to the enthalpy and entropy changes of the process as

(Δ G)_{P T} = Δ H - T Δ S

The magnitude of

Δ H

does not change much with the change in temperature but the entropy factor

T Δ S

changes appreciably. Thus, spontaneity of a process depends very much on temperature.

For the reaction at

298 K

2 A + B ⟶ C,

Δ H = 100 K c a l

and

Δ S = 0.020 K c a l K^{- 1}

. If

Δ H

and

Δ S

are assumed to be constant over the temperature range, at what temperature will the reaction become spontaneous?

Gibbs-Helmholtz equation relates the free energy change to the enthalpy and entropy changes of the process as

(Δ G)_{P T} = Δ H - T Δ S

The magnitude of

Δ H

does not change much with the change in temperature but the entropy factor

T Δ S

changes appreciably.
Thus, spontaneity of a process depends very much on temperature.

For the reaction at

25^{\circ} C

X_{2} O_{4} (l) ⟶ 2 X O_{2}

Δ H = 2.0 K c a l

and

Δ S = 20 c a l K^{- 1}

the reaction would be:

Q. Xenon forms 3 different Fluorides with

F_{2}

gas.
Look at the following reaction:

X e (g) + 2 F_{2} (g) \to X e F_{4} (s) Δ G

0

and choose theoretically appropriate arguments assuming the reaction is carried out in a sealed tube at a constant temperature T:

Q. Steam undergoes decomposition at high temperature as per the reaction

H_{2} O (g) ⇌ H_{2} (g) + \frac{1}{2} O_{2} (g), Δ H^{\circ} = 200 k J m o l^{- 1} Δ S^{\circ} = 40 J m o l^{- 1}

The temperature at which equilibrium constant is unit is :

Q. If the change in entropy

Δ S

is positive for an endothermic reaction and the enthalpy change

Δ H

occurs at the same temperature

T

, then the reaction is feasible________

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When CaCO3 is heated to a high temperature, it undergoes decomposition into CaCO and CO2 whereas it is quite stable at room temperature. The most likely explanation of it is:

The correct option is A The term TΔS overweight the enthalpy of reaction at high temperature ΔG=ΔH−TΔSAt high temperature TΔS factor dominates of ΔH and hence ΔG becomes negative and reaction occurs spontaneously.

When $C a C O_{3}$ is heated to a high temperature, it undergoes decomposition into $C a C O$ and $C O_{2}$
whereas it is quite stable at room temperature. The most likely explanation of it is:

The correct option is A The term $T Δ S$ overweight the enthalpy of reaction at high temperature
$Δ G = Δ H - T Δ S$
At high temperature $T Δ S$ factor dominates of $Δ H$ and hence $Δ G$ becomes negative and reaction occurs spontaneously.