mechanical equivalent of heat

(noun)

The work needed to produce the same effects as heat transfer.

Related Terms

Examples of mechanical equivalent of heat in the following topics:

  • Heat as Energy Transfer

    • This observation leads to the following definition of heat: Heat is the spontaneous transfer of energy due to a temperature difference .
    • James Prescott Joule (1818–1889) performed many experiments to establish the mechanical equivalent of heat—the work needed to produce the same effects as heat transfer.
    • In terms of the units used for these two terms, the best modern value for this equivalence is 1.000 kcal = 4186 J.
    • Figure 1 shows one of Joule's most famous experimental setups for demonstrating the mechanical equivalent of heat.
    • Schematic depiction of Joule's experiment that established the equivalence of heat and work

  • Internal Energy

    • James Joule showed that both heat and work can produce the same change in the internal energy of a substance, establishing the principle of the mechanical equivalence of heat.
    • It makes no sense to speak of the total 'heat' an object or system contains.
    • The internal energy of a system is the quantity that changes with the addition or subtraction of work or heat.
    • We can use statistical mechanics to relate the (somewhat) random motions of particles in a system to the mean kinetic energy of the ensemble of particles, and thus the empirically measurable quantity expressed as temperature.
    • Q is heat added to a system and Wmech is the mechanical work performed by the surroundings due to pressure or volume changes in the system.

  • Specific Heat for an Ideal Gas at Constant Pressure and Volume

    • The heat capacity at constant volume of nR = 1 J·K−1 of any gas, including an ideal gas is:
    • The heat capacity at constant pressure of 1 J·K−1 ideal gas is:
    • The heat capacity ratio or adiabatic index is the ratio of the heat capacity at constant pressure to heat capacity at constant volume.
    • His achievements were overlooked and credit for the discovery of the mechanical equivalent of heat was attributed to James Joule in the following year. von Mayer also proposed that plants convert light into chemical energy.
    • Potential energy stored in these internal degrees of freedom contributes to specific heat of the gas.

  • Heat and Work

    • The units of heat are therefore the units of energy, or joules (J).
    • For example, when heat transfers from the hot water at the bottom of the pot to the cooler water at the top of the pot.
    • When a high temperature body is brought into contact with a low temperature body, the temperatures equilibrate: there is heat flow from higher to lower temperature, like water flowing downhill, until the temperatures of the bodies are equivalent.
    • Work is the transfer of energy by any process other than heat.
    • There are many forms of work, including but not limited to mechanical, electrical, and gravitational work.

  • Specific Heat

    • 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.,
    • The specific heat of water is five times that of glass and ten times that of iron, which means that it takes five times as much heat to raise the temperature of water the same amount as for glass and ten times as much heat to raise the temperature of water as for iron.
    • To cause an equivalent temperature change in a doubled mass, you need to add twice the heat.
    • If it takes an amount Q of heat to cause a temperature change ΔT in a given mass of copper, it will take 10.8 times that amount of heat to cause the equivalent temperature change in the same mass of water assuming no phase change in either substance.

  • The Second Law

    • For example, heat involves the transfer of energy from higher to lower temperature.
    • Furthermore, mechanical energy, such as kinetic energy, can be completely converted to thermal energy by friction, but the reverse is impossible.
    • We shall see that the second law can be stated in many ways that may seem different, but these many ways are, in fact, equivalent.
    • The already familiar direction of heat transfer from hot to cold is the basis of our first version of the second law of thermodynamics.
    • (b) The brakes of this car convert its kinetic energy to heat transfer to the environment.

  • The Heat-Shock Response

    • Heat shock response is a cell's response to intense heat, including up-regulation of heat shock proteins.
    • Various bacterial mechanisms recognize different environmental changes and mount an appropriate response.
    • In biochemistry, heat shock is the "effect of subjecting a cell to a higher temperature than that of the ideal body temperature of the organism from which the cell line was derived. "
    • 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 .
    • Additionally, heat shock proteins are believed to play a role in the presentation of pieces of proteins (or peptides) on the cell surface to help the immune system recognize diseased cells.

  • Work

    • Thermodynamic work encompasses mechanical work (gas expansion, ) plus many other types of work, such as electrical.
    • As such, thermodynamic work is a generalization of the concept of mechanical work in mechanics.
    • Heat transfer (often represented by Q) and doing work (W) are the two everyday means of bringing energy into or taking energy out of a system.
    • Internal energy is a form of energy completely different from either heat or work.
    • Analyze the necessity to exclude energy transferred between system as heat from mechanical work

  • Multistep Transformations

    • One such example is the conversion of the sesquiterpene santonin into santonic acid on heating with base.
    • From the formulas shown in the following equation, shown in the first diagram below, this reaction not only adds one equivalent of water (expected if the lactone is opened), but also creates a new carbonyl group and removes both carbon-carbon double bonds.
    • The nature of the transformation of santonin to santonic acid remained unknown for many years, but was resolved in 1948 by the work of R.
    • The mechanism by which this remarkable change takes place is displayed above in the third diagram.
    • Initial hydrolysis of the lactone to santoninic acid is followed by isomerism of the α,β-unsaturation to a β,ν-location and tautomerization.

  • Overview of Heat

    • Energy can exist in many forms and heat is one of the most intriguing.
    • One of Maxwell's recommended books was Heat as a Mode of Motion by John Tyndall.
    • Maxwell outlined four stipulations for the definition of heat:
    • It cannot be treated as a substance, because it may be transformed into something that is not a substance, such as mechanical work.
    • Indirect estimation is the primary approach of many theoretical studies of quantity of heat transferred.