This is an example of an irreversible process. Even though Newton's Laws and The Laws of Conservation of Energy and Conservation of Momentum would be obeyed when you played the film backwards, the probability that all the milk and the glass would spontaneously come together to form a full glass of milk is incredibly small. If you videotaped the spill and then played the film backwards, it would be obvious to you that the film was running backwards. If you spill a glass of milk, what the glass and the milk droplets do is governed by the laws of physics. ΔS = nR ln(V f / V i) + nC V ln(T f / T i) If the heat transfer takes place over a range of temperatures then, as long as ΔT is small compared to the absolute temperature T, the change in entropy is approximately:įor an ideal gas, it can be shown that the change in entropy is given by: If the heat transfer takes place at a single temperature, the change in entropy is simply: The change in entropy is the heat added divided by the temperature at which the transfer took place. On the other, a change in entropy is easy to determine.Įntropy changes whenever there is a transfer of heat. ![]() Unlike P, V, and T, which are quite easy to measure, the entropy of a system is difficult to calculate. The symbol for entropy is S, and the units are J/K.Ī container of ideal gas has an entropy value, just as it has a pressure, a volume, and a temperature. ![]() Entropy is in some sense a measure of disorder.
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