How to Calculate Heat Transfer

Heat transfer is the exchange of thermal energies between physical systems depending on their temperature and pressure. It leads to change in the internal energies of the involved systems.There are three fundamental modes of heat transfer: conduction (heat transfer in solids); convection (heat transfer due to movement of liquids); and radiation (no medium for transfer required). Heat generally flows from a region of high temperature to a region of low temperature.


  1. Image titled Calculate Heat Transfer Step 1
    Learn the terms. Before you calculate the heat transferred in a process, it is recommended that you learn the basic terms involved in the calculation, so that you understand what is happening and you don't have to somehow just remember the formula until the examinations end. Make sure the knowledge stays with you.
    • Specific heat capacity of a substance: It is defined as the heat required to raise the temperature of a substance by '1 degree Celsius' or '1 Kelvin'. It is an extensive property, which means it depends on the amount of the substance (if you double the amount of the sample, the specific heat capacity of the substance also gets doubled).
    • The other terms involved are simply the 'mass of the substance' and the 'change in the temperature', which you obviously know about.
  2. Image titled Calculate Heat Transfer Step 2
    Learn the formula. The formula that is used in the calculation is: Q=CmT, where 'C' is the specific heat capacity of the substance whose temperature is raised, 'm' is the mass of the substance, and 'T' is the change in the temperature of the substance (final temperature minus the initial temperature).
  3. Image titled Calculate Heat Transfer Step 3
    Understand this with the help of an example. You have been given 10g of a substance X. Its temperature is 100 degree Celsius, and you have been told that the specific heat capacity of X is 2.5 J/K (that's its unit, note it down). You have to find out the amount of heat to be transferred to the substance so that we can raise its temperature by another 100 degree Celsius.
  4. Image titled Calculate Heat Transfer Step 4
    Consider the temperature change. It seems to be quite easy, right? But wait, what about the change in the temperature? The unit of temperature that you have been given in the data is 'degree Celsius', and the specific heat capacity of the substance involves the term 'Kelvin'! What do you do? Nothing, just remember a very important thing––a change of one degree Celsius is equivalent to change of one Kelvin. When you need to convert Celsius to Kelvin, you simply add 273 to the temperature. But while finding out the difference, that does not matter because the 273 gets added and then cancelled out.
    • So in this example, m=10g; C=2.5 J/K.Initial temperature=100 C=373 K; Final temperature=200 C=473 K; Change in temperature=(200-100 =100 degree Celsius) or (473-373=100 Kelvin). See, the change came to be the same, as long as you don't consider the units! After calculation you find out that Q=2500 joules. And there you go––it's this simple!


  • Q= msT where Q is the amount of heat gained or lost (transferred), m is the mass of the substance, s is specific heat capacity and T is the change in temp.
  • according to zeroth law of thermo dynamics heat lost by the hot body is equals to heat gained by the cold body.
  • consider two bodies of masses m1 and m2 and their initial temperatures are t1 and t2 and their specific heat capacities are s1 and s2. let say m1 is at higher temperature and m2 at lower. mix m1 and m2.
  • heat obviously transfer from m1 to m2 finally attains a equilibrium temp let us say t
  • heat lost by m1 =m1s1(t1-t)
  • heat gained by m2= m2s2(t-t2)


  • After you find out the change in the temperature without changing the unit of temperature into Kelvin, remember that you should not add 273 to the change thinking that it converts the unit to Kelvin. This mistake is done by many people, and is unfortunately found in many books too! If you want to satisfy yourself by converting the unit to Kelvin, first convert the unit of the initial and the final temperature into Kelvin and then find the difference.

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