eguruchela

Temperature and heat

Heat and temperature are related and often confused. More heat usually means a higher temperature. Heat is energy. It is the total amount of energy possessed by the molecules in a piece of matter. Heat is measured in Joules. Temperature is not energy. It relates to the average energy of microscopic motions of a single particle in the system per degree of freedom. It is measured in Kelvin (K), Celsius (C) or Fahrenheit (F).

“heat is the transfer of energy between two objects due to temperature differences.”

There is some circularity to the definitions used:

  • energy does work or produces heat, but
  • heat is a transfer of energy.

    • temperature is a property which is directly proportional to the kinetic energy of the substance under examination. temperature is the property which determines the direction heat will flow when two objects are brought into contact.

    Measuring Temprature

    A traditional thermometer measures temperature by containing a fluid that expands as it gets hotter and contracts as it gets cooler. As the temperature changes, the liquid within a contained tube moves along a scale on the device.

      Heat Temperature
    Symbol Q T
    Unit Joules Kelvin, Celsius or Fahrenheit
    SI unit Joule Kelvin
    Ability to do work Heat has the ability to do work Temperature can only be used to measure the degree of heat

    An ideal gas is defined as one in which all collisions between atoms or molecules are perfectly eleastic and in which there are no intermolecular attractive forces. One can visualize it as a collection of perfectly hard spheres which collide but which otherwise do not interact with each other. In such a gas, all the internal energy is in the form of kinetic energy and any change in internal energy is accompanied by a change in temperature. An ideal gas can be characterized by three state variables: absolute pressure (P), volume (V), and absolute temperature (T). The relationship between them may be deduced from kinetic theory and is called the

    Ideal Gas law = PV = nRT = NkT.

    n = number of moles

  • R = universal gas constant = 8.3145 J/mol K
  • N = number of molecules
  • k = Boltzmann constant = 1.38066 x 10-23 J/K = 8.617385 x 10-5 eV/K
  • k = R/NA
  • NA = Avogadro's number = 6.0221 x 1023 /mol
  • Temperature arises from the kinetic energy of the random motions of matter's particle constituents such as molecules or atoms. Therefore, it is reasonable to choose absolute zero, where all classical motion ceases, as the reference point.
  • By international agreement, the unit kelvin and its scale are defined by two points: absolute zero and the triple point of the standardized water.
  • At absolute zero, the particle constituents of matter have minimal motion and cannot become any colder. They retain minimal, quantum mechanical motion.