Energetics & electrochemistry · HL
Gibbs energy (HL)
Relate Gibbs energy to enthalpy, entropy or equilibrium.
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Number formats & units
Use decimal dots in datasets. Single values also accept decimal commas and scientific notation such as 1.2e-3 or 1.2 × 10⁻³.
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Result & working
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Formula & example
The relationship
What the variables mean
| Symbol | Meaning |
|---|---|
| Absolute temperature in K. | |
| 8.314462618 J mol⁻¹ K⁻¹. |
Worked example
- Calculation
- ΔG° from ΔH°, ΔS°, T
- ΔH° / kJ mol⁻¹
- -92.4
- ΔS° / J mol⁻¹ K⁻¹
- -198.0
- Temperature T / K
- 298.15
-33.3663 kJ mol⁻¹
Follow the example steps
- TΔS° = 298.15 × (-198) = -59033.7 J mol⁻¹ = -59.0337 kJ mol⁻¹
- ΔG° = ΔH° − TΔS° = -92.4 − (-59.0337) = -33.3663 kJ mol⁻¹
Common mistakes
Convert entropy from joules to kilojoules before combining units.
Incorrect approach
ΔG = 20 − 300 × 50 = −14980 kJ mol⁻¹
Correct approach
ΔG = 20 − 300 × 0.050 = 5 kJ mol⁻¹
More checks before you submit
- Convert ΔS° from J to kJ before combining with ΔH° in kJ.
Method notes
A negative ΔG° corresponds to K > 1 under the standard-state relationship. Spontaneity under non-standard conditions depends on composition as well as ΔG°.