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Standard XII

Chemistry

Gibbs Free Energy & Spontaneity

Considering ...

Question

Considering $△ G = △ H - T △ S$ , a spontaneous reaction will occur when :

△ G

is positive and

△ S

is positive

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△ G

is positive and

△ S

is negative

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△ H

is negative and

△ S

is positive

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△ H

is negative and

△ S

is negative

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△ H

is positive and

△ T

is negative

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Solution

The correct option is C $△ H$ is negative and $△ S$ is positive
$Δ G = Δ H - T Δ S$
For a spontaneous process, the change in Gibbs free energy $Δ G < 0$ .
Therefore, a spontaneous reaction will occur when $Δ H$ is negative and $Δ S$ is positive, which will make $Δ G$ value negative.

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Similar questions

Q. Assertion :A reaction will be spontaneous if

△

H is negative and

△

S is positive Reason:

△

G will be negative when there is a decrease in enthalpy and an increase in entropy

	Column I		Column II
a.	exothermic	p.	$H_{P} - H_{R}$
b.	endothermic	q.	$Δ H$ is negative
c.	spontaneous	r.	$Δ H$ is positive
d.	heat of reaction	s.	$Δ G$ is negative

Δ H

is positive and

Δ S

is negative then the reaction is:

Q. Free energy,

G = H - T Δ S

, is a state function that indicates whether a reaction is spontaneous or non-spontaneous. If you think of

T S

as the part of the system`s energy that is disordered already, then

(H - T S)

is the part of the system`s energy that is still ordered and therefore free to cause spontaneous change by becoming disordered.
Also,

Δ G = Δ H - T Δ S

From the second law of Thermodynamics, a reaction is spontaneous if

Δ_{t o t a l} S

is positive, non-spontaneous if

Δ_{t o t a l} S

is negative, and at equilibrium if

Δ_{t o t a l} S

is zero.

Since,

- T Δ S = Δ G

and since

Δ G

and

Δ S

have opposite signs, we can restate the Thermodynamic criterion for the spontaneity of a reaction carried out at a constant temperature and pressure.
If

Δ G < 0

, the reaction is spontaneous
If

Δ G > 0

, the reaction is non-spontaneous
If

Δ G = 0

, the reaction is at equilibrium

Read the above paragraph carefully and answer the following questions based on the above comprehension.

A particular reaction has a negative value for the free energy change. Then at ordinary temperature:

Q. Predict whether the reaction

C O (g) + (\frac{1}{2}) O_{2} (g) \to C O_{2} (g)

at 300 K is spontaneous & exothermic or non-spontaneous & endothermic, when the standard entropy change is

- 0.094 k J m o l^{- 1} K^{- 1} .

The standard Gibb's free energies of formation for

C O_{2}

and

C O

are

- 394.4 a n d - 137.2 k J m o l^{- 1}

respectively.

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Considering △G=△H−T△S, a spontaneous reaction will occur when :

The correct option is C △H is negative and △S is positiveΔG=ΔH−TΔS For a spontaneous process, the change in Gibbs free energy ΔG<0.Therefore, a spontaneous reaction will occur when ΔH is negative and ΔS is positive, which will make ΔG value negative.

Considering $△ G = △ H - T △ S$ , a spontaneous reaction will occur when :

The correct option is C $△ H$ is negative and $△ S$ is positive
$Δ G = Δ H - T Δ S$
For a spontaneous process, the change in Gibbs free energy $Δ G < 0$ .
Therefore, a spontaneous reaction will occur when $Δ H$ is negative and $Δ S$ is positive, which will make $Δ G$ value negative.