Thermodynamics: Energy, Entropy, and State Functions
Thermodynamics governs energy flow in chemical systems. The first law (ΔU = q + w) conserves energy; the second law introduces entropy. Gibbs free energy (ΔG = ΔH - TΔS) predicts spontaneity. State functions like U, H, S, and G depend only on the system state, not the path.
Why This Chemistry Calculation Matters
Why: Thermodynamics provides the framework for understanding reaction feasibility, heat engines, and phase equilibria. Enthalpy, entropy, and Gibbs energy are central to chemical and biochemical processes.
How: Select the calculation mode: Gibbs (ΔG from ΔH and ΔS), internal energy (ΔU = q + w), work (w = -PΔV), ideal gas (ΔU = nCvΔT), entropy, enthalpy, or process analysis. Enter values and apply the appropriate equations.
- ●State functions (U, H, S, G) are path-independent; q and w are not.
- ●Isothermal: ΔT = 0; adiabatic: q = 0; isobaric: P constant; isochoric: V constant.
- ●For ideal gases, ΔU depends only on temperature (ΔU = nCvΔT).
Compact Examples
Inputs
For educational and informational purposes only. Verify with a qualified professional.
🔬 Chemistry Facts
First law: ΔU = q + w (energy conservation).
— IUPAC
Gibbs free energy: ΔG = ΔH - TΔS predicts spontaneity.
— NIST
Work at constant P: w = -PΔV.
— Thermodynamics
Ideal gas: ΔU = nCvΔT; Cv = 3R/2 (monatomic), 5R/2 (diatomic).
— Kinetic theory
📋 Key Takeaways
- • ΔG = ΔH - TΔS | Gibbs free energy predicts spontaneity
- • ΔU = q + w | First law: internal energy = heat + work
- • w = -PΔV | Work at constant pressure
- • ΔG < 0 | Spontaneous; ΔG > 0 non-spontaneous
Did You Know?
ΔH < 0 means exothermic; heat released to surroundings.
Source: IUPAC
At ΔG = 0, T = ΔH/ΔS is the critical temperature.
Source: Equilibrium
Isothermal: ΔT = 0; adiabatic: q = 0.
Source: Process types
ΔU = nCvΔT for ideal gas at constant volume.
Source: Ideal gas
NIST-JANAF tables provide standard ΔH, ΔS, ΔG.
Source: NIST
Work done by system: w < 0; on system: w > 0.
Source: Sign convention
How the Thermodynamics Calculator Works
Select mode: Gibbs (ΔG), Internal Energy (ΔU), Work, Ideal Gas, Entropy, Enthalpy, or Process Analysis. Enter values; calculator applies ΔG = ΔH - TΔS, ΔU = q + w, w = -PΔV, etc.
Gibbs
ΔG = ΔH - TΔS
First Law
ΔU = q + w
Expert Tips
Use Kelvin
T in ΔG = ΔH - TΔS must be in K.
Sign Convention
q > 0: heat in; w < 0: work by system.
Units
ΔH in kJ/mol; ΔS in J/(mol·K).
Critical T
T = ΔH/ΔS when ΔG = 0.
Key Formulas
| Quantity | Formula |
|---|---|
| ΔG | ΔH - TΔS |
| ΔU | q + w |
| w | -PΔV |
| ΔU (ideal gas) | nCvΔT |
| ΔH | nCpΔT |
Frequently Asked Questions
What is ΔG?
Gibbs free energy; ΔG < 0 means spontaneous at constant T, P.
Why is ΔG = ΔH - TΔS?
Combines enthalpy and entropy to predict spontaneity.
What is the first law?
ΔU = q + w; energy change = heat + work.
When is w = -PΔV?
Reversible work at constant pressure.
Why use Kelvin for T?
ΔG equation requires absolute temperature.
What is critical temperature?
T where ΔG = 0; T = ΔH/ΔS (when ΔS ≠ 0).
Key Numbers
📚 Official Sources
⚠️ Disclaimer: Uses IUPAC/NIST conventions. Consult NIST-JANAF, IUPAC Gold Book, and Atkins for precise work.
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