Thermodynamic Facts



  • Energy cannot be destroyed but it can be burned up. Every time energy is used, some turns into heat. This is why you feel hot after running.
  • Energy that turns into heat may not be lost. It dissipates (spreads out thinly in all directions) and is hard to use again.
  • Every time energy is used, some free energy (available to make things happen) gets lost as heat.
  • Scientists use the word ‘entropy’ to describe how much energy has become unusable. The less free energy there is, the greater the entropy.
  • The word ‘entropy’ was invented by the German physicist Rudolf Clausius in 1865.
  • Clausius showed that everything really happens because energy moves from areas of high energy to areas of low energy, from hot areas to cold areas.
  • Energy goes on flowing from high to low until there is no difference to make anything happen. This is an equilibrium state. Entropy is the maximum.
  • Energy cannot be reused once it has turned to heat and dissipated, just as you cannot rebuild an igloo once the snow has melted.
  • Clausius summed this idea up in 1860s with two laws of thermodynamics.
  • The first law of thermodynamics says the total energy in the Universe was fixed forever at the beginning of time.
  • The second law of thermodynamics says that energy is dissipated every time it is used. So the entropy of the Universe must increase.