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• Heat


  Energy that is transferred from one body to another as the result of a difference in temperature
• Two bodies at different temperatures are brought together

  Energy is transferred (heat flows) from the hotter body to the colder
• Heat transfer


  Usually results in an increase in the temperature of the colder body and a decrease in the temperature of the hotter body
• Substance absorbing heat


  May not increase in temperature by changing from one physical state (or phase) to another (e.g. solid to liquid, solid to vapour, liquid to vapour, one solid form to another)
• Heat


  A form of energy
• Temperature


  A measure of the amount of energy present in a body
• The distinction between heat and temperature was clarified during the 18th and 19th centuries
• Heat transfer


  1. Conduction in solids or fluids at rest

  2. Convection in liquids or gases in a state of motion, combining conduction with fluid flow

  3. Radiation, which takes place with no material carrier
• Flow of heat in metal bars studied analytically by Jean-Baptiste-Joseph Fourier and measured by Jean-Baptiste Biot

  1816
• Conductivity of water first determined

  1839
• Conductivity of gases measured

  After 1860
• Biot formulated the laws of conduction

  1804
• Fourier published a mathematical description of conduction


  1822
• Infrared rays found to be reflected and refracted as visible light

  1803
• Kirchhoff presented his law of radiation, relating emissive power to absorptivity


  1859
• Stefan established the Stefan-Boltzmann law relating the energy radiated by a blackbody and the fourth power of its temperature


  Unknown
• Boltzmann established the mathematical basis for the Stefan-Boltzmann law


  1884
• Newton suggested an equation describing heat transfer by convection


  1701
• Understanding of heat transfer by convection developed

  1880-1920
• It was in the study of radiation that Max Planck arrived at the concept of the quantum
• Sensible heat


  Energy necessary to produce a particular temperature change excluding any energy required for a phase change
• Latent heat


  Energy necessary to change a liquid to a vapour at constant temperature and pressure
• Heat of fusion


  Energy required to melt a solid to a liquid
• Heat of sublimation


  Energy necessary to change a solid directly to a vapour
• All changes of state occur under conditions of constant temperature and pressure
• Units of heat


  Calorie, British Thermal Unit (BTU)
• One BTU is approximately 252 calories
• Heat capacity


  The amount of energy required to raise a unit mass of a substance through a specified temperature interval
• Specific heat


  The heat capacity of a substance
• Specific heat depends on whether heat is added at constant volume or constant pressure
• The law of Dulong and Petit related the heat capacities of many solid elements to their atomic weights
• Deviations from the law of Dulong and Petit were later explained by quantum mechanics