Change in entropy is also a function of temperature, at any temperature, the entropy change can be given as: ΔS=∫dqT. Q. The entropy change can be calculated by using the expression ΔS=qrevT. Change in entropy: The formula for the change in entropy of a process can me expressed mathematically as Δ S = Q T (J K) where is the the heat transfer and is the temperature at which the process takes place.