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Science Class 11 - Heat And-Thermodynamics Notes

Comprehensive study notes for Class 11 - Heat And-Thermodynamics olympiad preparation

Heat and Thermodynamics

Welcome to the chapter on Heat and Thermodynamics for Class 11. In this chapter, you will learn about the concepts of heat, temperature, thermal equilibrium, and the laws of thermodynamics. By the end of this chapter, you will understand how energy is transferred as heat, how systems reach equilibrium, and how the laws of thermodynamics govern physical processes.

Key Concepts

  • Heat: A form of energy transferred between systems or objects with different temperatures.
  • Temperature: A measure of the average kinetic energy of the particles in a substance.
  • Thermal Equilibrium: When two objects in contact have the same temperature and no heat flows between them.
  • Thermodynamics: The study of heat, work, and the energy transformations in physical systems.

Heat and Temperature

  • Heat is measured in joules (J) or calories (cal).
  • Temperature is measured in degrees Celsius (°C), Kelvin (K), or Fahrenheit (°F).
  • Heat flows from a hotter object to a colder one until thermal equilibrium is reached.

Thermal Expansion

Most substances expand when heated and contract when cooled. This is called thermal expansion.

  • Linear expansion: Change in length.
  • Areal expansion: Change in area.
  • Volume expansion: Change in volume.

Specific Heat Capacity

The amount of heat required to raise the temperature of 1 kg of a substance by 1°C is called its specific heat capacity (c).

Formula: Q = mcΔT
Where Q = heat supplied, m = mass, c = specific heat capacity, ΔT = change in temperature.

Change of State and Latent Heat

When a substance changes its state (solid to liquid, liquid to gas), it absorbs or releases heat without a change in temperature. This heat is called latent heat.

  • Latent heat of fusion: Heat required to change a solid to a liquid at constant temperature.
  • Latent heat of vaporization: Heat required to change a liquid to a gas at constant temperature.

Laws of Thermodynamics

  • Zeroth Law: If two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other.
  • First Law: Energy cannot be created or destroyed, only changed from one form to another. (ΔU = Q - W)
  • Second Law: Heat cannot spontaneously flow from a colder body to a hotter body. Entropy of an isolated system always increases.
  • Third Law: As temperature approaches absolute zero, the entropy of a perfect crystal approaches zero.

Thermodynamic Processes

  • Isothermal: Temperature remains constant (ΔT = 0).
  • Adiabatic: No heat exchange (Q = 0).
  • Isochoric: Volume remains constant (ΔV = 0).
  • Isobaric: Pressure remains constant (ΔP = 0).

Applications of Thermodynamics

  • Engines and refrigerators work on the principles of thermodynamics.
  • Understanding weather, climate, and biological processes.
  • Industrial processes like power generation and chemical manufacturing.

Practice Questions

  1. Define specific heat capacity and write its formula.
  2. State the first law of thermodynamics.
  3. What is latent heat of fusion? Give an example.
  4. Explain the difference between isothermal and adiabatic processes.
  5. Why does ice at 0°C feel colder than water at 0°C?

Challenge Yourself

  • Calculate the heat required to raise the temperature of 500 g of water from 20°C to 80°C. (Specific heat of water = 4200 J/kg°C)
  • Describe a real-life example where the second law of thermodynamics applies.

Did You Know?

  • The Kelvin scale starts at absolute zero, the lowest possible temperature.
  • The concept of entropy explains why some processes are irreversible.

Glossary

  • Heat: Energy transferred due to temperature difference.
  • Temperature: Measure of the average kinetic energy of particles.
  • Entropy: Measure of disorder or randomness in a system.
  • Thermodynamics: Study of heat, work, and energy transformations.

Answers to Practice Questions

  1. Specific heat capacity is the amount of heat required to raise the temperature of 1 kg of a substance by 1°C. Formula: Q = mcΔT
  2. The first law states that energy cannot be created or destroyed, only transformed. ΔU = Q - W
  3. Latent heat of fusion is the heat needed to change a solid to a liquid at constant temperature. Example: Melting ice to water.
  4. Isothermal: temperature constant; Adiabatic: no heat exchange.
  5. Because ice absorbs latent heat from your hand to melt, making it feel colder.

Understanding heat and thermodynamics helps explain many natural and technological processes around us!

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