16: Entropy and Free Energy Flashcards
What is entropy (S)
a measure of how dispersed the energy in the system is
What are the units of entropy
JK¯¹mol¯¹
Does an increase in disorder, increase or decrease entropy
It increases the dispersal of energy and hence leads to an increase in entropy
Put solid, liquid and gas in order of entropy state
Highest to lowest
Gas, liquid, solid
Why will ΔS always be positive for vapourisation and melting processes
Because the particles have much greater freedom in a less ordered state so they have a higher entropy
How to calculate ΔS of a reaction
Entropy of products - entropy of reactants
What is molar entropy (Sϴ)
Entropy of 1 mole of a substance under standard conditions
For a reaction to be feasible, what must the sign of ΔG be
negative
What is the units for ΔG
kJmol¯¹
So make sure ΔS is in kJK¯¹mol¯¹ not JK¯¹mol¯¹
If ΔH is positive and ΔS is negative, is the reaction feasible
It is never feasible
As ΔG would be positive at all temperatures
Endothermic reactions can never happen unless what?
They are accompanied by an entropy increase
If ΔH is positive and ΔS is positive will the reaction ever be feasible
It will only be feasible after a certain minimum temperature at which TΔS outweighs ΔH
If ΔH is negative and ΔS is positive, will the reaction ever be feasible
It will always be feasible
As ΔG is negative at all temperatures
If ΔH is negative and ΔS is negative, will the reaction ever be feasible
Yes but only below a maximum temperature
Just because a reaction has a negative ΔG it still might not happen. Why?
It could be very very slow (has a very high activation energy)
