Thermodynamics - Entropy
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What is a feasible reaction?
A reaction that can occur at a particular temperature without being driven by external influences
Why may a feasible reaction not occur?
Because the activation energy is too high for it to proceed
For what set of values of total entropy change is a reaction feasible?
When delta Stotal is greater than zero
For what set of values of change in gibbs free energy is a reaction feasible?
When Gibbs free energy is less than or equal to zero
What is a spontaneous reaction?
A spontaneous reaction is one that is feasible and occurs under standard conditions
What are the conditions needed for a reaction to be spontaneous?
When Gibbs free energy is less than or equal to zero and the activation energy is low enough for the reaction to take place under standard conditions
What can be said about a reaction that is feasible but not spontaneous?
It has a high activation energy
What is entropy?
A measure of the disorder of particles (the number of arrangements particles can make)
What are standard entropy values?
The molar entropy of the pure substance in its standard state at 100kPa and the temperature of interest
What is the symbol for entropy?
S
What are the units of entropy?
JK-1mol-1
What is the link between the entropy value and the amount of disorder in a substance?
The higher the entropy value the more disordered a substance
What factors affect entropy?
State, temperature, number of moles and Mr
How does state affect entropy?
As you go from solid to liquid to gas the entropy increases
Why do solids have a low entropy value?
Very regular and ordered arrangements so there are few ways in which particles can arrange themselves
Why is there a larger increase in entropy between liquids to gases than solids to liquids?
Gases are more disordered so the particles can form more arrangements
How does temperature affect entropy?
The higher the temperature the greater the entropy bc the more disordered the particles become
How does Mr affect entropy?
The higher the Mr of substances in the same state the higher the entropy
How does the number of particles affect the entropy?
The more particles the higher the entropy value because the more arrangements the particles can make
What is the third law of thermodynamics?
At 0K there is 0 entropy bc the substance is a perfectly ordered crystalline substance
What is the melting point?
The increase in entropy between the solid and the liquid
What is the boiling point?
The increase in entropy between the liquid and the gas
How do you calculate the entropy of a system?
Sum of entropy of products - sum of entropy of reactants
How do you calculate the entropy of the surroundings?
-deltaH/temperature