heat

Examples of heat in the following topics:

• Specific Heat

  • The specific heat is an intensive property that describes how much heat must be added to a particular substance to raise its temperature.
  • The heat capacity is an extensive property that describes how much heat energy it takes to raise the temperature of a given system.
  • This quantity is known as the specific heat capacity (or simply, the specific heat), which is the heat capacity per unit mass of a material .
  • The specific heat is the amount of heat necessary to change the temperature of 1.00 kg of mass by 1.00ºC.
  • Note that the total heat capacity C is simply the product of the specific heat capacity c and the mass of the substance m, i.e.,

• Water’s High Heat Capacity

  • The high heat capacity of water has many uses.
  • The heat is quickly transferred to a pool of water to cool the reactor.
  • The capability for a molecule to absorb heat energy is called heat capacity, which can be calculated by the equation shown in the figure .
  • Water has the highest specific heat capacity of any liquid.
  • Specific heat is defined as the amount of heat one gram of a substance must absorb or lose to change its temperature by one degree Celsius.

• Specific Heat and Heat Capacity

  • the molar heat capacity, which is the heat capacity per mole of a pure substance.
  • the specific heat capacity, often simply called specific heat, which is the heat capacity per unit mass of a pure substance.
  • Now we can plug our values into the formula that relates heat and heat capacity:
  • Latent heat of melting describes tœhe amount of heat required to melt a solid.
  • The above simulation demonstrates the specific heat and the latent heat.

• Heat Pumps and Refrigerators

  • A heat pump is a device that transfers heat energy from a heat source to a heat sink against a temperature gradient.
  • Heat pumps, air conditioners, and refrigerators utilize heat transfer from cold to hot.
  • Actually, a heat pump can be used both to heat and cool a space.
  • As with heat pumps, work input is required for heat transfer from cold to hot.
  • What is considered the benefit in a heat pump is considered waste heat in a refrigerator.

• The Heat-Shock Response

  • Heat shock response is a cell's response to intense heat, including up-regulation of heat shock proteins.
  • Heat shock response is the cellular response to heat shock includes the transcriptional up-regulation of genes encoding heat shock proteins (HSPs) as part of the cell's internal repair mechanism .
  • HSPs are also called 'stress-proteins' and respond to heat, cold and oxygen deprivation by activating several cascade pathways.
  • The up-regulation of HSPs during heat shock is generally controlled by a single transcription factor; in eukaryotes this regulation is performed by heat shock factor (HSF), while σ32 is the heat shock sigma factor in Escherichia coli.
  • Heat shock protein come in many sizes.

• Overview of Heat

  • Energy can exist in many forms and heat is one of the most intriguing.
  • This module defines and explores heat transfer, its effects, and the methods by which heat is transferred.
  • Maxwell outlined four stipulations for the definition of heat:
  • After defining and quantifying heat transfer and its effects on physical systems, we will discuss the methods by which heat is transferred.
  • So many processes involve heat transfer, so that it is hard to imagine a situation where no heat transfer occurs.

• Heat and Work

  • Heat transfer by convection occurs through a medium.
  • Lastly, heat can also be transferred by radiation; a hot object can convey heat to anything in its surroundings via electromagnetic radiation.
  • Like heat, the unit measurement for work is joules (J).
  • Heat and work are related.
  • Work can be completely converted into heat, but the reverse is not true: heat energy cannot be wholly transformed into work energy.

• Heat Engines

  • In thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work.
  • In thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work .
  • We define the efficiency of a heat engine (Eff) to be its net work output W divided by heat transfer to the engine Qh:
  • (b) A heat engine, represented here by a circle, uses part of the heat transfer to do work.
  • Qh is the heat transfer out of the hot reservoir, W is the work output, and Qc is the heat transfer into the cold reservoir.

• Heat as Energy Transfer

  • Heat is the spontaneous transfer of energy due to a temperature difference.
  • This observation leads to the following definition of heat: Heat is the spontaneous transfer of energy due to a temperature difference .
  • Heat is often confused with temperature.
  • Heat is a form of energy, whereas temperature is not.
  • We use the phrase "heat transfer" to emphasize its nature.

• Heating Curve for Water

  • Water transitions from ice to liquid to water vapor as heat is added to it.
  • A heating curve shows how the temperature changes as a substance is heated up at a constant rate.
  • A constant rate of heating is assumed, so that one can also think of the x-axis as the amount of time that goes by as a substance is heated.
  • Instead, use the heat of fusion ($\Delta H_{fusion}$ ) to calculate how much heat was involved in that process: $q=m\cdot \Delta H_{fusion}$, where m is the mass of the sample of water.
  • Use the heat of vaporization ($\Delta H_{vap}$ ) to calculate how much heat was absorbed in this process: $q=m\cdot C_{H_2O(g)}\cdot \Delta T$, where m is the mass of the sample of water.