BIOCHEM 5721 Entropy

Section 1: Order, Microstates, and Work (Slide 3)

Q1.1: Why does creating or restoring specific configurations require work? Provide the three lecture examples.

Ordered state is very rare, where as a mixed or uniform state contains vast numbers of possible arrangements. System naturally evolve toward disordered state unless work is done to maintain or restore order.

Section 2: Heat Capacity, Modes, and Thermodynamic Entropy (Slide 4)

Q2.1: What is heat capacity C at the molecular level, and why does it differ so drastically across Argon, Water, and Lysozyme?

Heat capacity C(T) is the energy required to increase the temperature of a substance by 1K by adding energy into its unconsidered degrees of freedom (modes). Adding 1K shifts the average kinetic energy/speed of the population, not any single individual molecule.

When you raise the temperature by 1 K, energy is added across all of these available modes to shift the population average. Argon has the lowest heat capacity because it only has translational mode while lysozyme has a larger heat capcity because it has thousands of internal modes absorbing energy.

Q2.2: What are the thermodynamic definitions and formulas for entropy (S)?

Entropy is the integrated total of each increment of reversible heat divided by temperature at which it is added (dS)= (delta q-rev/ T). When heat capacity is constant across a temperature range (integrated form), change in entropy is ∆S= Cln (T2/T1).

blob

blob