What is the first law of thermodynamics?

The first law of thermodynamics states that energy can neither be created nor destroyed; it can only change forms. Mathematically, ΔU = Q - W.

What does Gibbs free energy indicate?

Gibbs free energy determines whether a reaction is spontaneous. If ΔG is negative, the process is spontaneous under constant temperature and pressure.

What is the relationship between Gibbs energy and equilibrium constant?

The relationship is given by ΔG° = -RT ln K, where K is the equilibrium constant, R is the gas constant, and T is the absolute temperature.

Thermodynamic Equations and Functions

Explore the key thermodynamic equations and concepts that govern energy changes, spontaneity, and equilibrium in physical and chemical systems. Thermodynamic Equations and Functions

Important Thermodynamic Functions

Internal Energy (U): Total energy contained within a system, including molecular kinetic and potential energies.
Enthalpy (H): Heat content at constant pressure, defined as H = U + PV.
Entropy (S): Measure of disorder or randomness in a system.
Gibbs Free Energy (G): Maximum useful work at constant temperature and pressure, G = H – TS.
Helmholtz Free Energy (A or F): Work obtainable at constant volume and temperature, A = U – TS.

Key Thermodynamic Equations

1. First Law of Thermodynamics: ΔU = Q – W

ΔU = change in internal energy, Q = heat added, W = work done by the system.

2. Enthalpy Change: ΔH = ΔU + PΔV

3. Gibbs Free Energy: ΔG = ΔH – TΔS

4. Helmholtz Free Energy: ΔA = ΔU – TΔS

5. Relation to Equilibrium Constant: ΔG° = -RT ln K

Explanation

First Law: Energy is conserved; internal energy changes depend on heat and work.
Enthalpy: Useful for reactions at constant pressure (heat absorbed or released).
Gibbs Free Energy: Determines spontaneity — a negative ΔG indicates a spontaneous process.
Helmholtz Free Energy: Useful in systems at constant volume.
Equilibrium: When ΔG° = 0, the system is at equilibrium and K determines reaction extent.

Learn more about Entropy and Spontaneity.

MCQ Quiz – Thermodynamic Functions

Which thermodynamic function is defined as H = U + PV?
a) Internal Energy
b) Enthalpy
c) Gibbs Free Energy
d) Entropy
Answer: b) Enthalpy
Explanation: Enthalpy includes internal energy plus pressure–volume work.
What does the first law of thermodynamics state?
a) Energy can be created
b) Energy can be destroyed
c) Energy is conserved
d) Energy is infinite
Answer: c) Energy is conserved
Explanation: Energy cannot be created or destroyed, only transformed.
Gibbs free energy helps predict:
a) Temperature change
b) Volume change
c) Reaction spontaneity
d) Pressure
Answer: c) Reaction spontaneity
Explanation: A negative ΔG indicates a spontaneous reaction.
The equation ΔG° = -RT ln K relates:
a) Free energy and entropy
b) Free energy and equilibrium constant
c) Enthalpy and work
d) Internal energy and pressure
Answer: b) Free energy and equilibrium constant
Explanation: It connects Gibbs free energy with the equilibrium position of a reaction.

Frequently Asked Questions

1. What is the importance of Gibbs Free Energy?

Gibbs free energy helps predict whether a chemical reaction is spontaneous under constant temperature and pressure.

2. What does ΔH signify in thermodynamics?

ΔH (enthalpy change) represents heat absorbed or released by a system during a chemical reaction at constant pressure.

3. What happens when ΔG° = 0?

When ΔG° equals zero, the system is at equilibrium, meaning no net reaction occurs.

Up Next: Entropy – Understanding Disorder and Spontaneity

(Learn more on Wikipedia).