The Laws of Thermodynamics: Essential Concepts of Heat
What is Heat?
Heat is a form of energy that is transferred between objects or systems due to a temperature difference. It flows naturally from regions of higher temperature to regions of lower temperature. Heat is denoted by the symbol Q or q and its SI unit is Joules(J). Also measure in calories.
Key Concepts in Heat
- Temperature vs. Heat:
- Temperature measures the hotness or coldness of an object, related to the average kinetic energy of particles.
- Heat is the energy transfer due to temperature differences.
- Thermal Energy:
The total internal energy(ΔU) of a system, including the kinetic and potential energies of its particles. - Heat Transfer Mechanisms:
- Conduction: Transfer of heat through direct contact between particles (e.g., metal rod heated at one end).
- Convection: Transfer of heat in fluids (liquids and gases) through bulk movement (e.g., boiling water).
- Radiation: Transfer of heat via electromagnetic waves, without needing a medium (e.g., sunlight). It is fastest method of heat transfer.
Measurement of Heat
- Specific Heat Capacity (c):
The amount of heat required to change the temperature of 1 kg of a substance by 1°C.
Formula:Q=mcΔT, where Q= heat energy, m= mass, ΔT= temperature change. - Latent Heat:
Heat absorbed or released during a phase change without a temperature change (e.g., melting or boiling).
Formula:Q=mL, where L= latent heat, m= mass.
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 (Law of Energy Conservation):
The change in internal energy of a system is equal to the heat added to the system minus the work done by the system:- ΔU=Q−W
- Second Law:
Heat flows spontaneously from hot to cold bodies, and entropy (disorder) tends to increase. - Third Law:
As the temperature approaches absolute zero, the entropy of a system approaches a minimum value.
Applications of Heat
- Everyday Life: Cooking, heating homes, refrigeration.
- Industrial: Metallurgy, power plants, chemical processes.
- Scientific: Thermodynamics, astrophysics, climate science.
- Transportation: Internal combustion engines, jet propulsion.
- Medicine: Sterilization, thermotherapy.
Practical Examples
- Boiling Water: Convection currents transfer heat throughout the water.
- Metal Spoon in Hot Soup: Heat is conducted through the metal spoon.
- Sunlight: Radiative heat warms the Earth.
Important Heat-Related Phenomena
- Thermal Expansion:
Most materials expand when heated. This principle is used in bimetallic strips and thermal sensors. - Phase Changes:
- Melting, freezing, boiling, condensation, sublimation.
- Energy is exchanged during these changes, but temperature remains constant.
- Heat Engines:
Devices like steam engines, car engines, and turbines that convert heat into work.
Units and Conversions
- 1 calorie (cal)=4.184 Joules (J)
- 1kWh (kilowatt-hour)= 3.6×106J