What is thermodynamics?

Thermodynamics is the branch of chemistry that deals with the study of energy changes during chemical and physical processes. It focuses on macroscopic properties like temperature, pressure, volume, and internal energy, and how they influence the energy transformations of a system.

What is a thermodynamic system?

A thermodynamic system is the part of the universe under study, while the rest of the universe is called the surroundings.
System + Surroundings = Universe

What are the different types of thermodynamic systems?

• Open System – Exchanges both matter and energy with surroundings (e.g., boiling water in an open pot).
• Closed System – Exchanges only energy but not matter (e.g., water in a sealed flask).
• Isolated System – No exchange of energy or matter (e.g., an ideal thermos flask).

What are state functions?

State functions depend only on the initial and final states of a system and not on the path taken.

Examples: Internal energy (U), Enthalpy (H), Entropy (S), Gibbs Free Energy (G), Pressure (P), Volume (V), Temperature (T).

What is the First Law of Thermodynamics?

• The First Law of Thermodynamics states that energy can neither be created nor destroyed, only transferred or converted from one form to another. Mathematically, 
  ΔU=q+w
  where:
• ΔU = Change in internal energy
• q = Heat added (+) or removed (-)
• w = Work done on (+) or by (-) the system

How is work related to pressure and volume?

Work done in a pressure-volume process is given by:

W = −PextΔV

where:

• Pext = External pressure
• ΔV = Change in volume

For reversible isothermal expansion of an ideal gas:

• n= number of moles of gas
• R = universal gas constant (8.314 J/mol·K)
• T = temperature in Kelvin

What is enthalpy?

Enthalpy (H) is the total heat content of a system. It is defined as:

H=U+PV 

where:

• H = Enthalpy
• U = Internal energy
• P = Pressure
• V = Volume

What is the relationship between enthalpy and internal energy?

At constant pressure, the change in enthalpy is:

ΔH = ΔU+PΔV

where ΔH is heat absorbed/released at constant pressure.

What is heat capacity?

Heat capacity (C) is the amount of heat required to raise the temperature of a substance by 1°C (or 1K).
Types of Heat Capacity:

• Specific Heat Capacity (c): Heat required to raise 1g of a substance by 1°C. q=mcΔT where m = mass, c = specific heat, ΔT = temperature change.
• Molar Heat Capacity (C_m): Heat required to raise 1 mole of a substance by 1°C.

What is the relationship between Cp and Cv for an ideal gas?

For an ideal gas,

Cp−Cv = R

where R is the gas constant.

What is a thermochemical equation?

A thermochemical equation is a balanced chemical equation that includes the enthalpy change (ΔH).
Example:

(-) ΔH means exothermic, (+) ΔH means endothermic.

What is Hess’s Law?

Hess’s Law states that the total enthalpy change in a reaction is the same whether it occurs in one step or multiple steps.
ΔH overall = ∑ ΔH Steps

What is entropy?

Entropy (S) is a measure of disorder or randomness in a system. Higher entropy means greater disorder.

What is the Second Law of Thermodynamics?

The Second Law of Thermodynamics states that the entropy of the universe always increases in a spontaneous process.
Mathematically,
ΔS universe =ΔS system + ΔS surroundings>0
for a spontaneous process.

What is Gibbs Free Energy?

Gibbs Free Energy (G) predicts the spontaneity of a reaction.
ΔG=ΔH−TΔS
where:

• ΔG < 0 → Reaction is spontaneous.
• ΔG > 0 → Reaction is non-spontaneous.
• ΔG = 0 → System is in equilibrium.

What are the different types of enthalpy changes in chemical reactions?

1. Enthalpy of Formation (ΔH⁰_f) → Heat change when 1 mole of a compound is formed from its elements in their standard states.

2. Enthalpy of Combustion (ΔH⁰_c) → Heat released when 1 mole of a substance burns completely in oxygen.

3.  Enthalpy of Neutralization (ΔH⁰_n) → Heat released when 1 mole of H⁺ reacts with 1 mole of OH⁻ to form water.

4. Enthalpy of Solution (ΔH⁰_sol) → Heat change when 1 mole of a substance dissolves in a solvent.

How is Gibbs free energy related to the equilibrium constant?

Gibbs free energy change (ΔG) and the equilibrium constant (K) are related by the equation:

ΔG °= −RTln⁡K

where:

• ΔG° = Standard Gibbs free energy change
• R = Gas constant (8.314 J/mol·K)
• T = Temperature in Kelvin
• K = Equilibrium constant
• If ΔG° < 0, then K > 1, and the reaction is spontaneous.
• If ΔG° > 0, then K < 1, and the reaction is non-spontaneous.
• If ΔG° = 0, then K = 1, and the system is at equilibrium.

What is the Third Law of Thermodynamics?

The Third Law of Thermodynamics states that the entropy of a perfect crystalline substance at absolute zero (0 K) is zero.

Mathematically,

• S=0 at T=0K

This means that at absolute zero temperature, all molecular motion ceases, and the system is in a perfectly ordered state.

How does temperature affect the spontaneity of a reaction?

The spontaneity of a reaction depends on ΔG = ΔH - TΔS: