5.2.2 Enthalpy And Entropy Flashcards
What is entropy?
A measure of the dispersal of energy in a system or the degree of disorder.
What is standard entropy?
Entropy of 1 mole of a substance under standard conditions.
What are the units for standard entropy change?
JK-1mol-1
When is ΔS positive?
When a system becomes more disordered, so entropy increases.
Examples of entropy increase?
- Change of state from solid to liquid/gas.
- Dissolving solid lattice to form solution.
- Reactions where there is an increase in the number of moles of gas.
When are reactions more stable?
When there is more disorder, so particles will try to move and increase entropy.
How come some reactions are feasible even if they are endothermic?
To become more energetically stable as ΔS is positive.
What is it called when a substance reaches max entropy state?
Thermodynamically stable.
What is ΔS when a system becomes less disordered?
-ve.
How do you calculate ΔS?
Sum of entropy of the products - sum of entropy of the reactants.
What do you need to remember to do to ΔS to use it in another equation?
Convert to kJ
What is the equation for free energy?
ΔG = ΔH - TΔS
What is T measured in?
Kelvin.
When are reactions always feasible?
When ΔH is negative and ΔS is positive.
When are reactions never feasible?
When ΔH is positive and ΔS is negative.
