Lecture Fifteen - Entropy and the second law of thermodynamics Flashcards
What is the law of conservation of energy?
The total energy of the universe is constant and cannot be made or destroyed.
Are spontaneous reactions always exothermic?
No, they can be endothermic. But in order to be spontaneous, no work is required. Work is required for non-spontaneous reactions.
Define entropy.
Entropy is the degree of disorder in a system. A change in order is a change in the number of ways of arranging the particles, and it is a ket factor in determining the direction of a spontaneous process.
What is Boltzmann’s formula?
S = k ln W. Where K = Boltzmann’s constant (R/Na) (Gas constant on Avogadro’s number). Where W = measure of probability number of ways atoms can be arranged with no change in energy.
What are microstates?
Microstates = a statistical distribution of energy.
How does entropy change as states change?
Solid -> liquid -> gas Increasing disorder –> Increasing entropy –>
What is the standard molar entropy?
The entropy per mole of a pure substance while in its standard state (1 atm (gas), I M (solution), or pure substance (solid)).
What factors effect the entropy of a system?
1) Temperature changes - entropy increases as temperature increases.
2) Physical states and phase changes
- Entropy increases as more ordered phase changes to a less ordered phase (solid -> liquid -> gas).
Note that there is a jump between each state for entropy.
3) Dissolution of a solid or a liquid
- Entropy of a dissolved solid or liquid is usually granter than the entropy of the pure solute.
However, the extent depends upon the nature of the solute and solvent.
4) Dissolution of a gas
- A gas becomes more ordered when it dissolved in a liquid or solid.
5) Size of molecules
- As molecular size increase, the entropy increases.
The greater the number of vibrational and/or rotational modes, the higher the entropy.
What kind of function is entropy?
A state function.
As with any other state function, standard molar entropies can be combined to find the standard entropy of reaction.
