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14.1 Heat

3 min readLast Updated on June 18, 2024

Heat transfer is a crucial concept in physics, involving the movement of thermal energy between objects. It occurs through conduction, convection, and radiation, each with unique characteristics and applications in everyday life and technology.

Understanding heat transfer is essential for grasping thermodynamics, which explores the relationship between heat, energy, and work. This knowledge helps explain various phenomena, from phase changes to thermal expansion, and has practical applications in engineering and everyday life.

Heat and Energy Transfer

Energy transfer through heat

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  • Heat transfers thermal energy from a hotter object to a colder object
    • Thermal energy flows from high temperature to low temperature until thermal equilibrium is reached where both objects have the same temperature
  • Heat transfer occurs through three main mechanisms
    • Conduction transfers thermal energy through direct contact between particles in solids, liquids, and gases at a rate depending on the material's thermal conductivity (metals)
    • Convection transfers thermal energy through the movement of fluids as heated fluid expands, becomes less dense, and rises, while cooler fluid sinks, creating a convection current (boiling water)
    • Radiation transfers thermal energy through electromagnetic waves without requiring a medium and can occur in a vacuum with emission and absorption depending on the object's temperature and surface properties (sunlight)
      • The Stefan-Boltzmann law describes the total energy radiated per unit surface area of a black body across all wavelengths per unit time

Conversions between heat and work

  • The mechanical equivalent of heat relates the amount of work done to the amount of heat generated as demonstrated by Joule's experiment showing a specific amount of work always produces the same amount of heat
  • The relationship between heat and work is given by Q=WQ = W where QQ is the heat generated and WW is the work done, both measured in joules
  • The specific heat capacity cc of a substance relates the amount of heat required to change its temperature using the equation Q=mcΔTQ = mc\Delta T where
    1. QQ is the heat transferred in joules
    2. mm is the mass of the substance in kilograms
    3. cc is the specific heat capacity in joules per kilogram per kelvin
    4. ΔT\Delta T is the change in temperature in kelvins

Effects of heat on substances

  • Internal energy is the sum of the kinetic and potential energies of the particles within a substance which can change by heat transfer altering the kinetic and potential energies of its particles
  • When heat is added to a substance, its particles gain kinetic energy, resulting in an increase in temperature with the amount of change depending on the substance's specific heat capacity (water vs. metal)
  • Phase changes occur when a substance absorbs or releases heat without a change in temperature
    • Melting changes a solid to a liquid and requires heat input known as the heat of fusion (ice melting)
    • Vaporization changes a liquid to a gas and requires heat input known as the heat of vaporization (boiling water)
    • Condensation changes a gas to a liquid and releases heat (steam condensing)
    • Freezing changes a liquid to a solid and releases heat (water freezing)
  • The energy required for phase changes depends on the substance's latent heat
    • Latent heat of fusion is the energy required to change a substance from solid to liquid or released during freezing (ice)
    • Latent heat of vaporization is the energy required to change a substance from liquid to gas or released during condensation (steam)
  • Thermodynamics is the study of heat, temperature, and their relation to energy and work
  • Entropy is a measure of the disorder or randomness in a system, which tends to increase in natural processes
  • Heat capacity is the amount of heat required to raise the temperature of an object by one degree, related to but distinct from specific heat capacity
  • Thermal expansion is the tendency of matter to change its shape, area, and volume in response to a change in temperature

Term 1 of 24

Change in entropy
See definition

Change in entropy is the measure of the disorder or randomness in a system as it undergoes a process. It quantifies the energy dispersal and unavailability for doing work.

Key Terms to Review (24)

Term 1 of 24

Change in entropy
See definition

Change in entropy is the measure of the disorder or randomness in a system as it undergoes a process. It quantifies the energy dispersal and unavailability for doing work.

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AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.

Term 1 of 24

Change in entropy
See definition

Change in entropy is the measure of the disorder or randomness in a system as it undergoes a process. It quantifies the energy dispersal and unavailability for doing work.



© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.

© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.
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