Thermodynamics 11 Class Notes Fighter JEE 2025.pdf

FIGHTER JEE 2025 PHYSICAL CHEMISTRY Lecture - 11 THERMODYNAMICS

Instructor: Mohan Sir (CMS Sir)

Platform: Physics Wallah

Topics to be Covered

1. Thermochemistry

   • Study of heat changes that occur during chemical reactions and changes of state.

   • Importance in understanding energy transfers in physical and chemical processes.

2. Enthalpy of Formation

   • Defines the heat change when one mole of a compound is formed from its elements in their standard states.

   • Essential for calculating reaction enthalpies using Hess's Law.

3. Enthalpy of Neutralization

   • Specific enthalpy change when one equivalent of an acid reacts with one equivalent of a base to form water and a salt.

   • Usually negative for strong acids and bases indicating exothermic nature.

4. Enthalpy of Combustion

   • Measures the heat released when a compound undergoes complete combustion in oxygen.

   • Important for energy content calculations in fuels.

Determining Spontaneity of a Process

Conditions for Spontaneous Processes:

1. ΔH > 0 and ΔS < 0 - Non-spontaneous at all temperatures.

2. ΔH < 0 and ΔS > 0 - Always spontaneous (exothermic processes).

3. ΔH < 0 and ΔS < 0 - Spontaneous at low temperatures (exothermic but with a decrease in disorder).

4. ΔH > 0 and ΔS > 0 - Spontaneous at high temperatures (endothermic processes with an increase in disorder).

Temperature for Spontaneity

Example Calculation: Given: ΔH = 200 J/mol, ΔS = 40 J/K·mol To find Minimum Temperature (T) for spontaneity:

ΔG = ΔH - TΔS For spontaneity, ΔG must be less than 0.

Choices for Minimum Temperature:

• (a) 20K

• (b) 4K

• (c) 5K

• (d) 12K

Enthalpy Changes in Reactions

Reaction Representation:

• A general reaction can be represented as:

aA + bB ⇌ cC + dD

• ΔH: Total enthalpy change during the reaction can be either positive (endothermic) or negative (exothermic).

Types of Reactions

1. Exothermic Reactions

   • Heat is released to the surroundings, indicated by ΔH < 0.

   • Examples: Combustion (e.g., burning of hydrocarbons), Neutralization reactions.

2. Endothermic Reactions

   • Heat is absorbed from the surroundings, indicated by ΔH > 0.

   • Examples include photosynthesis and certain dissolution processes.

Factors Affecting ΔH of Reactions

• Reaction Conditions:

  • Most reactions are conducted under constant temperature and pressure or volume.

  • Under constant T and P, we have.

  • Enthalpy of Reaction (ΔH) is a key indicator of heat exchange during chemical processes.

Physical State of Reactants and Products

• The enthalpy change for reactions can vary significantly depending on the physical state of the reactants and products:

  • Example: H₂(g) + O₂(g) → H₂O(l)

  • The physical state (gas vs liquid) influences ΔH values due to the intermolecular forces involved.

Modes of Representation of Reactions

• Notation and Enthalpy Changes:

  • Different representations can indicate ΔH changes based on various states and conditions of reactants.

  • Kirchoff's Equation: Shows relationship between temperature changes and enthalpic changes in reactions.

Standard Enthalpy of Reaction

• Defined as the enthalpy change for a reaction when all reactants and products are in their standard states (1 bar pressure for gases and specific concentrations for solutions).

Types of Enthalpy

1. Enthalpy of Formation:

   • Significant for determining stability and reactivity as it measures energy change when forming one mole of a compound from its elements.

   • Reference states for elements are defined specifically for thermodynamic calculations.

Example of Enthalpy Calculation

• The calculation method of enthalpy changes using standard values:

  • Formula: ΔH = {(ΣΔH products) - (ΣΔH reactants)}

Application of the Enthalpy of Formation

• Includes practical examples to calculate enthalpy changes in specific reactions, example:

  • N₂(g) + 3H₂(g) → 2NH₃(g)

Heat Calculation at Constant Pressure

• An example of calculating the overall heat of formation:

  • Reaction: F₂O(g) + H₂O(g) → O₂(g) + 2HF(g)

  • Demonstrates the heat required defined by the heat values of reactants.

Heat Requirement for Reaction Formation

• Calculation example for determining the heat for forming a specific mass of a compound:

  • Example: 1.28 kg of CaC₂ requiring 2240 kcal, including reactant values for CaO, CaC₂, and CO.

Enthalpy of Neutralization

• Defining the enthalpy change associated with neutralizing a defined amount of acid and base, typically one equivalent:

  • The example discusses diverse strong acid/base reactions leading to salt and water.

Example of Neutralization Reaction

• Reaction Example: HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

  • Standard values of enthalpy change for the reaction are noted for strong acids and bases evaluated.

Homework Assignment

• DPP-08 homework assigned to reinforce topics covered in this lecture.

Conclusion

• Closure and acknowledgment of participants for engaging in the lecture, encouraging further exploration of thermodynamic principles.