Entropy

Classic and statistical definition of entropy

 Entropy(∆𝑆) is the quantity denoting increase in disorder.

Classic

Heat exchange is when heat is transferred from a body of higher temperature to a body of lower temperature, in a voluntary process the system entropy increases. The higher temperature body loses more heat than lower temperature body gains.

        ∆𝑆 = ∆𝑄/𝑇

Statistic

Based on particle model, the system is stable if only few deviations are made from the distribution of particles over a given time at given volume and internal energy.

• Microstate

Microscopic information tells us the speed and location of particles but nothing on the systems. This info indicates the microstate.

• Macrostate

Macroscopic information only gives volume, energy and particle number. It is the measure of Boltzmann entropy, which is max. at equilibrium.

        𝑆 = 𝑘 ∗ 𝑙𝑛𝑊

W is number of microstates.

Second law of thermodynamics

 Entropy of isolated system does not decrease over time. Work can be completely converted to heat but not to work.

Perpetual motion of second type

A machine allowing energy to be converted into different forms without loss. It should be possible for the machine to perform work by cooling a reservoir and withdrawing same amount of heat but 2nd law contradicts this because according to Planck the machine can’t do more than lift a load and cool the reservoir. Thermal energy can’t be fully converted to work.

Gibbs free energy, combines entropy, enthalpy and temperature.

     ∆𝐺 = ∆𝐻 − 𝑇 ∗ ∆𝑆

At constant temperature and pressure spontaneous reaction only occurs if ∆𝐺