Which reaction below is spontaneous at SATP?


Which reaction below is spontaneous at SATP?
∆Hº=34.1 kJ and ∆Sº=46.2 J/K
∆Hº=71.7 kJ and ∆Sº=-4.25 J/K
∆Hº=-11.1 kJ and ∆Sº=-61.8 J/K
∆Hº=9.95 kJ and ∆Sº=57.4 J/K

When ∆G is positive, a chemical reaction is
faster
spontaneous
slower
non-spontaneous

Step 1 of 2

Given data: ∆Hº=34.1 kJ and ∆Sº=46.2 J/K
∆Hº=71.7 kJ and ∆Sº=-4.25 J/K
∆Hº=-11.1 kJ and ∆Sº=-61.8 J/K
∆Hº=9.95 kJ and ∆Sº=57.4 J/K

Find: When ∆G is positive, a chemical reaction is faster, spontaneous, slower or non-spontaneous.

Explanation:

we can use the Gibbs free energy (ΔG) relationship:

ΔGHTΔS

Step 2 of 2

To determine spontaneity, we can use the Gibbs free energy (ΔG) relationship:

ΔGHTΔS

where:

  • ΔG is the Gibbs free energy change,
  • ΔH is the enthalpy change,
  • ΔS is the entropy change,
  • T is the temperature in Kelvin.

For a reaction to be spontaneous at a given temperature, ΔG must be negative.

Now let’s analyze each reaction:

  1. ΔH∘=34.1kJ and ΔS∘=46.2J/K ΔG=34.1−T(0.0462)
  2. ΔH∘=71.7kJ and ΔS∘=−4.25J/K ΔG=71.7−T(−0.00425)
  3. ΔH∘=−11.1kJ and ΔS∘=−61.8J/K ΔG=−11.1−T(−0.0618)
  4. ΔH∘=9.95kJ and ΔS∘=57.4J/K ΔG=9.95−T(0.0574)

Explanation:

For spontaneity, we want ΔG<0. Check the sign of ΔG for each reaction based on the given values of ΔH and ΔS.

Final solution

Additionally, when ΔG is positive, a chemical reaction is non-spontaneous.

Therefore, the spontaneous reaction at SATP is the one where ΔG is negative. Identify the reaction with ΔG<0.

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