Entropic forces

Chapter 6 considers ways in which a system can be 'open'. In section 6.5.2 the effect of an external mechanical force is considered. A rod of length L and area A is pushed into the system with fext along L, the free energy change depends only on TS:

This equation is from Sekur-Tetrode. We find that N, T, A and total energy are all constant - this means that the free energy change only depends on L and the force that causes this is found by:

Remembering that when free energy is minimised, no more work can be extracted we can find the maximum possible extracted work to be F - Fmin.

This force will be important when considering the apparent forces that cause proteins to fold and emphasises the usefulness of the concept of free energy.

The next section following discusses that the process of free energy transduction (of which this was one example) and states that the most efficient transduction happens when the energy is released in small controlled steps. A good example of this is the electron transport chain in ATP synthesis.