**How to calculate change in entropy**

**05/13/17**

*“How can we calculate the change in entropy for a thermodynamic process?”*

It is well known that for all thermodynamic processes, there is a corresponding increase in entropy in the entire system. However, how can we **quantitatively measure** such a change? Well, after many years of research, physicists and engineers have been able to come up with an **equation** which states that the change in entropy for a **reversible process** is equal to the** time integral of change of heat divided by the initial temperature,** or **(delta)s=integral(**dq**/T)**. From this, we can derive that for an isothermal expansion or contraction, the equation will be (delta)S=nRln(vf/v0), and (delta)d=-nRln(pf_p0), while in cooling or heating a system it will be (delta)s=ncln(tf/t0) and for a phase transition it will be (delta)s=(delta)h/T.

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