Chapter 14 - Entropy and Gibbs Energy Flashcards
Can absolute values for entropy be calculated?
Yes they can.
This is calculated using the Boltzmann formula.
What is a perfect crystal?
All of the atoms, ions or molecules of a substance are aligned perfectly and with no defects.
Why is the entropy of a perfect crystal zero at 0K?
There is only a single way of arranging the molecules and these molecules are not moving which gives a perfectly ordered system.
W = 1, so S = 0.
What is the 3rd Law of Thermodynamics?
The entropy of a perfect crystal at zero kelvin is zero.
What is residual entropy?
Despite the molecules not moving (0K), a molecule can have more than one orientation which gives the molecule entropy.
This can arise due to different orientations of molecules and/or isotopes.
What is an adiabatic process?
A process where there is no exchange of heat with the surroundings.
What is dynamic equilibrium?
The rate of the forward reaction equals the reverse reaction and there is no net change in composition.
What are thermodynamics and kinetics used for in equilibrium reactions?
Thermodynamics is used to find the equilibrium composition.
Kinetics is used to assess how quickly the equilibrium is reached.
What is activity defined as for ideal gases?
Partial pressure.
What is activity defined as for ideal solutions?
Concentration.
In a reaction that goes to completion, what happens to the Gibbs free energy?
It decreases continually but at any stage is less than zero.
What is the value for Gibbs free energy when the forward reaction is spontaneous, at equilibrium and when the backward reaction is spontaneous?
Forward reaction is spontaneous - ΔG < 0.
At equilibrium - ΔG = 0
Backward reaction is spontaneous - ΔG > 0.
What is Le Chatelier’s Principle?
When a change is made to a system in dynamic equilibrium, the equilibrium responds so as to minimise the effect of the change.
What graph does the Van’t Hoff equation make?
A straight line graph when a graph a of ln(K) vs. 1/T.
The gradient of the slope is -ΔH/R.
What direction is the Van’t Hoff graph for endothermic and exothermic reactions?
Exothermic - the slope is positive.
Endothermic - the slope is negative.
