THERMODYNAMICS – PART 2
1. ENTHALPY CHANGE (ΔH)
- Enthalpy (H) = U + PV
- Change in Enthalpy: ΔH = ΔU + PΔV
Types of Enthalpy Changes:
• Heat of reaction (ΔHrxn)
• Heat of formation (ΔHf)
• Heat of combustion (ΔHc)
• Heat of neutralization (ΔHn)
2. HEAT CAPACITY AND ITS TYPES
- Heat Capacity (C) = q / ΔT
- Specific Heat Capacity (per gram)
- Molar Heat Capacity (per mole)
3. RELATION BETWEEN Cp AND Cv
For ideal gases:
Cp - Cv = R
Where R = universal gas constant
4. HESS’S LAW OF CONSTANT HEAT SUMMATION
The total enthalpy change for a reaction is the same, no matter how many steps it takes.
Example:
ΔH (A → D) = ΔH (A → B) + ΔH (B → C) + ΔH (C → D)
5. SPONTANEITY OF A PROCESS – ΔG CRITERIA
Gibbs Free Energy Equation:
ΔG = ΔH - TΔS
Spontaneity Conditions:
| ΔH | ΔS | ΔG | Process |
|-----|-----|----------|-----------------|
|- |+ |- | Spontaneous |
| - | - | Depends | Spontaneous at low T |
| + | + | Depends | Spontaneous at high T |
|+ |- |+ | Non-spontaneous |
1. ENTHALPY CHANGE (ΔH)
- Enthalpy (H) = U + PV
- Change in Enthalpy: ΔH = ΔU + PΔV
Types of Enthalpy Changes:
• Heat of reaction (ΔHrxn)
• Heat of formation (ΔHf)
• Heat of combustion (ΔHc)
• Heat of neutralization (ΔHn)
2. HEAT CAPACITY AND ITS TYPES
- Heat Capacity (C) = q / ΔT
- Specific Heat Capacity (per gram)
- Molar Heat Capacity (per mole)
3. RELATION BETWEEN Cp AND Cv
For ideal gases:
Cp - Cv = R
Where R = universal gas constant
4. HESS’S LAW OF CONSTANT HEAT SUMMATION
The total enthalpy change for a reaction is the same, no matter how many steps it takes.
Example:
ΔH (A → D) = ΔH (A → B) + ΔH (B → C) + ΔH (C → D)
5. SPONTANEITY OF A PROCESS – ΔG CRITERIA
Gibbs Free Energy Equation:
ΔG = ΔH - TΔS
Spontaneity Conditions:
| ΔH | ΔS | ΔG | Process |
|-----|-----|----------|-----------------|
|- |+ |- | Spontaneous |
| - | - | Depends | Spontaneous at low T |
| + | + | Depends | Spontaneous at high T |
|+ |- |+ | Non-spontaneous |
