Entropy and Free Energy Flashcards
What is entropy?
A measure of the amount of disorder of a system.
What does a high entropy mean?
There will be more disorder/dispersal.
What are the units for entropy?
JK-1 mol-1.
What is the trend of entropy in solids, liquids and gases?
- Solids have the smallest entropy.
- Liquids have greater entropies.
- Gases have the greatest entropies.
What is the entropy at 0K?
There would be no energy and all substances would have an entropy value of zero.
How does the entropy value change as the system changes to be more random?
Energy can be spread out more so there will be an entropy change which will be positive.
How does the entropy value change as the system changes to be less random?
Energy becomes more concentrated and so the entropy change will be negative.
What happens when substances change state from solid to liquid to gas have an increased entropy?
The melting points and boiling points increase the randomness of the particles and so energy is more spread out so the change is positive.
How can you predict entropy values by just the number of molecules?
If there are less gas molecules in the products than the reactants, there is a more negative entropy value.
What is the standard entropy (S)? Units?
The entropy of one mole of substance, under standard conditions - JK-1 mol-1.
What entropy value is standard entropy always?
Positive.
What is the standard entropy equation?
(Sum of standard entropy of products) - (Sum of standard entropy of reactants).
What is feasibility?
Used to describe whether a reaction is able to happen and is energetically feasible.
What is free energy change (G)?
The overall change in energy during a chemical reaction.
What are the 2 types of free energy (G)?
- Enthalpy change H - the heat transfer between the chemical system and the surroundings.
- The entropy change at the temperature of the reaction TS - the dispersal of energy within the chemical system itself.
What is the Gibbs’ equation?
G = H = TS:
- T is the temperature in kelvin.
What is the condition that a reaction is feasible?
There must be a decrease in free energy (G).
What must the values in the Gibbs’ equation be?
Kj K-1 mol-1.
How do you work out the minimum temperature for feasibility?
Use the equation:
H - TS = 0.
Can endothermic processes also be feasible?
Yes, at room temperature, you need to calculate G from the Gibbs’ equation using the temperature given in kelvin and prove that it is a negative number, so reaction is feasible.
What is the limitation of predictions made for feasibility?
Many reactions have a negative G and still do not seem to take place.
Why do some reactions with negative G values not take place/are not feasible?
Because of the very high activation energy resulting in a slow rate, so DOES NOT TAKE INTO ACCOUNT OF THE KINETICS OR RATE OF THE REACTION.
