For a reaction, [tex]\Delta H = 198 \text{ kJ}[/tex]. For which value of [tex]T \Delta S[/tex] is the reaction spontaneous?

A. -198 kJ
B. 198 kJ
C. 0 kJ
D. 396 kJ

Question

Middle School

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Answer :

mariejoepagaduan mariejoepagaduan · Answer 1 · 2024-09-16T06:55:25-04:00

The correct answer is D. 396 kJ. ΔG will be negative for this value of TΔS indicating a spontaneous reaction.

Further Explanation:

The value of the Gibbs Free Energy (ΔG) determines the spontaneity of the reaction.
To get this value, an equation than shows the relationship among the Gibbs Free Energy (ΔG), enthalpy (ΔH), entropy (ΔS), and temperature is used: [tex]dG \ = dH \ - TdS[/tex]
A positive ΔG represents a non-spontaneous reaction
A negative ΔG value indicates a spontaneous reaction.

A. -198 kJ FALSE because this gives a positive ΔG.

[tex]dG \ = \ 198 \ kJ \ - \ (-198 \ kJ) \\\boxed {dG = 396 \ kJ}[/tex]

B. 198 kJ FALSE because this results in ΔG = 0. The reaction is at equilibrium.

[tex]dG \ = \ 198 \ kJ \ - \ 198 \ kJ \\\boxed {dG = 0}[/tex]

C. 0 kJ FALSE because this results in a positive ΔG.

[tex]dG = 198 \ kJ \ - \ 0\\\boxed {dG = 198 \ kJ}[/tex]

D. 396 kJ TRUE because this results in a negative ΔG.

[tex]dG = \ 198 \ kJ \ - \ 396 \ kJ\\\boxed {dG = -198 \ kJ}[/tex]

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Keywords: Gibbs Free Energy, spontaneity