Heat

what is heat

The heat is the process of energy transfer that flows between a system and its environment because of the temperature difference between them.

To better understand what heat is, let’s use the following analogy. Heat is vehicle traffic on a highway, while vehicles are energy. If there is no vehicle circulation, there is no traffic, just as if there is no energy transfer, there is no heat.

The transfer of energy or heat is established between a body and the environment that surrounds it when there is a difference in temperature. This transfer ends when thermal equilibrium is reached, that is, when the temperature between the parts is the same.

diagram of energy transfer as heat

Scheme of heat or energy transfer between the environment and a body TA is the ambient temperature; TC is the body temperature.

For example, when we dip a cold spoon into a cup of hot tea, the spoon gets hotter and the tea gets colder until they both reach the same temperature. There is a transfer of energy from the tea to the spoon due to the temperature difference.

The mechanisms of energy transfer as heat are:

  • heat conductionOccurs when two parts of a material are kept at different temperatures. For example, when you touch a hot pot, energy is transferred by conduction from the pot to your hand.
  • heat convection: occurs when a fluid flows through a temperature difference.
    This is what happens when you turn on the heater in a room: the air around the heater heats up and rises, while the cold air sinks.
  • thermal radiation: occurs when heat is established between bodies that are not in contact, as occurs between the Sun and the Earth.
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Specific heat

Specific heat is the amount of energy that needs to be transferred to one kilogram of a substance to increase its temperature by one degree. This physical quantity is represented by the lowercase letter “c” and depends on the material and the pressure.

For example, to raise the temperature of 1 kelvin of 1 kilogram of water, 4190 joules need to be transferred, so the specific heat of water is 4190 Joule/kg.K. To raise the temperature of one kilogram of iron by one degree, 462 Joules are needed (c=462 Joule/kg.K).

This means that to heat water it is necessary to transfer more energy than to heat the same amount of iron.

To find the specific heat of a substance we calculate its mass (m) and its heat capacity (C), which is the amount of heat that this substance can absorb. The formula used is:

começar style mathematical size 14px heat specific space space stand left challenge c stand straight equal to numerator capacity heat space over denominator mass fim da fraction equal to challenge C over challenge m end of style

See more about Specific Heat.

Latent heat

Latent heat is the amount of heat transferred to a unit mass of a substance to change its state.

  • latent heat of fusion: is the amount of heat that must be transferred for a solid to become a liquid; is denoted as LF.
    For example, the latent heat of fusion of water is 334,103 J/kg, which means that to melt 1 kilogram of water, the transfer of 334,103 joules of energy is required.
  • latent heat vaporization: the amount of energy that must be transferred for a liquid to pass into the gaseous state; is denoted as Lv.
    For example, the latent heat of vaporization of water is 2260 103 J/kg, that is, it takes 2260 103 J of energy to evaporate one kilogram of water.
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Difference Between Heat and Temperature

We must not confuse “heat” with “temperature”. While heat is a process where energy is transferred, temperature is a measure of the average internal movement of the atoms or molecules of a body or substance. Thus, the greater the internal movement of the particles of a material, the higher the temperature.

Temperature can be measured on different scales: Kelvin (K), degrees Celsius or Centigrade (º C), or degrees Fahrenheit (ºF). To measure the temperature of a body we place the thermometer in contact with it.

The units for measuring heat are the joule, which is the fundamental unit of energy in the International System. However, in some contexts the calorie is used.

The calorie (cal) is defined as the amount of energy required to raise the temperature of 1 gram of water from 14.5 ºC to 15.5 ºC, specifically. In this sense, 1 calorie is equal to 4,186 joules.

See also:

  • Temperature
  • Calorie
  • Evaporation
  • Fusion

References

Belendez, A. (2017). Heat and temperature. Physical Foundations of Engineering I. Accessed May 2022 at https://rua.ua.es/dspace/bitstream/10045/95287/1/Tema-4-Calor-y-temperatura.pdf

Gomez, ALB, & Hernandez, AS (2010). Detection and classification of conceptual errors in heat and temperature. Latin-American Journal of Physics Education, 4(2), 21.

Resnick R, Halliday D, Krane KS (2013). Physics volume 1, 4th ed. Homeland Publishing Group. Mexico.