Thermodynamics HSC Overview

Thermodynamics HSC Overview

• Thermodynamics is a fundamental topic in 12th HSC Physics, focusing on heat, energy, and work.

Thermodynamic Terms

• System: The part of the universe being studied (e.g., gas in a cylinder).
• Surroundings: Everything outside the system.
• Boundary: Separates the system from its surroundings.
• Open System: Exchanges both energy and matter with surroundings.
• Closed System: Exchanges energy, but not matter.
• Isolated System: Exchanges neither energy nor matter.

Thermodynamic Processes

• Isothermal Process: Temperature remains constant (T = 0). Heat supplied equals work done by the system (Q = W).
• Adiabatic Process: No heat exchange (Q = 0). Work done changes internal energy (W = -∆U).
• Isochoric Process: Volume remains constant (∆V = 0). No work is done (W = 0). Heat added equals change in internal energy (Q = ∆U).
• Isobaric Process: Pressure remains constant (∆P = 0). Change in internal energy and work are related as follows (∆U = Q - W).

Laws of Thermodynamics

• Zeroth Law: If two systems are in thermal equilibrium with a third, they are in equilibrium with each other. Basis of temperature measurement.
• First Law: Energy is conserved. Change in internal energy (∆U) plus work done (W) equals heat added (Q). (∆U + W = Q).

Internal Energy (U)

• The sum of kinetic and potential energies of molecules.
• Depends only on the state of the system (state function).

Heat Capacity

• Specific Heat Capacity (c): Heat required to raise the temperature of 1 kg of a substance by 1°C. (Q = mc∆T)
• Molar Heat Capacity (C): Heat required to raise the temperature of 1 mole of a substance by 1°C. (Q = mc∆T, where m is now the number of moles).

Work Done in Thermodynamics

• General Formula: W = PAV, where: P = pressure, and ∆V = change in volume.
• Work in different processes has specific formulas (e.g., isothermal, adiabatic)

Entropy (S)

• A measure of disorder or randomness in a system.
• Change in Entropy (∆S) = Qrev/T (Qrev = heat exchanged in a reversible process).
• Second Law of Thermodynamics relates to Entropy (irreversible processes, ∆S > 0; reversible processes, ∆S = 0).

Carnot Engine

• System with components: high-temperature reservoir, low-temperature reservoir, and working substance.
• Efficiency (η) = 1 - Tc/TH (Tc = temperature of sink, TH = temperature of source).

Applications of Thermodynamics

• Heat engines, refrigerators, air conditioners, thermal power plants rely on thermodynamic principles.

Basic Definitions (Theory-Based Questions)

• Define the terms system, surroundings, and boundary.
• Explain open, closed, and isolated systems with examples.
• State and explain the First Law of Thermodynamics.
• Explain the Second Law of Thermodynamics with the Kelvin-Planck and Clausius statements.
• Explain the significance of the third law of thermodynamics.
• State and Define entropy.
• Describe the formula for entropy change in a reversible process explain how entropy relates to the second law of thermodynamics.
• Describe the working of a Carnot engine with a neat labeled diagram and derive the formula for the efficiency of a Carnot engine.
• What is the coefficient of performance (COP) of a refrigerator?

Derivations (Theory-Based Questions)

• Derive the expression for work done in an isothermal process
• Derive the expression for work done in an adiabatic process.
• Derive the relation between Cp and Cv
• Derive the efficiency formula for a Carnot engine.
• Prove that in an adiabatic process: PV γ = constant

Numerical Problems

• A gas undertakes adiabatic expansion; calculate the change in internal energy.
• A system absorbs heat and performs work; calculate the internal energy change.

Conceptual Questions

• Why is it impossible to construct a 100% efficient heat engine?
• Why is entropy considered a measure of disorder?
• What is the difference between reversible and irreversible processes?
• Why is the second law of thermodynamics called the "arrow of time"?
• Why can the temperature of a system never reach absolute zero?

Important Questions (Previous Year Question Papers)

• List of important questions based on thermodynamics
• Solutions/answers