Instructions
Total Questions: 20 | Marks: 4 each | No Negative Marking
Thermodynamics – IIT JEE Notes (Set 8)
First Law of Thermodynamics
Statement
The first law states that heat supplied to a system is used to change its internal energy and to do work.
Formula: ΔQ = ΔU + W
Key Insight
It is based on the law of conservation of energy.
Internal Energy
Definition
Internal energy is the total energy of all molecules in a system.
Important Point
For an ideal gas, internal energy depends only on temperature, not on pressure or volume.
Isothermal Process
Concept
In this process, temperature remains constant.
Relation
PV = constant
Key Insight
Heat supplied is completely converted into work done.
Adiabatic Process
Concept
No heat exchange occurs between system and surroundings.
Equation
PVγ = constant
Key Insight
Temperature changes due to work done.
Isochoric Process
Concept
Volume remains constant.
Important Point
Work done is zero since there is no change in volume.
Isobaric Process
Concept
Pressure remains constant.
Work Done
W = PΔV
Heat Capacity
Definition
Heat required to raise temperature of a substance by 1 K.
Units
J/K
Types
Specific heat, molar heat capacity, Cp and Cv.
Ratio of Heat Capacities
Formula
γ = Cp / Cv
Key Insight
Important for adiabatic processes and speed of sound calculations.
Ideal Gas Equation
Formula
PV = nRT
Key Insight
Relates pressure, volume, temperature, and number of moles.
Work Done in Thermodynamics
Concept
Work done by a gas is positive during expansion and negative during compression.
Graph Insight
Area under PV curve represents work done.
Second Law of Thermodynamics
Statement
Heat cannot flow from a colder body to a hotter body without external work.
Key Insight
Introduces concept of irreversibility and efficiency limits.
Entropy
Definition
Entropy is a measure of disorder or randomness of a system.
Formula
ΔS = Q / T
Key Insight
Entropy always increases in irreversible processes.
Carnot Engine
Efficiency
η = 1 – (T₂ / T₁)
Important Point
Efficiency depends only on temperatures of source and sink.
Heat Transfer
Modes
Conduction, convection, and radiation.
Key Insight
Heat always flows from higher temperature to lower temperature.
Zeroth Law of Thermodynamics
Statement
If two systems are in thermal equilibrium with a third system, they are in equilibrium with each other.
Application
Basis for temperature measurement.
Important Exam Concepts
Conceptual Traps
Work done is zero in isochoric process. Internal energy of ideal gas does not depend on pressure or volume.
JEE Strategy
Focus on process-based questions, PV diagrams, and conceptual clarity rather than rote formulas.