Enthalpy, entropy and free energy

Question 1

Define entropy.

Answer 1

A measure of disorder or randomness

Question 2

What is the order of randomness

Answer 2

Solid - least
Liquid - middle
Gas - most

Question 3

What is the sign for entropy and what is it measured in

Answer 3

△S⦵, a change in entropy has a +ve △S⦵ value if there has been an increase in disorder. Measured in JK-1mol-1

Question 4

What do all substances have at true 0, 0Kelvin

Answer 4

They all have an entropy of 0 as they are in perfect order

Question 5

What does a positive and negative entropy state?

Answer 5

\+△S⦵ = increase in entropy 
-△S⦵ = decrease in entropy

Question 6

What is the equation for △S⦵?

Answer 6

△S⦵ = Sum of S⦵ products - Sum of △S reactants

Question 7

What is a feasible reaction?

Answer 7

A reaction for which △G < 0

Question 8

What is the equation and units for △G

Answer 8

△G⦵ = △H - T△S⦵, where T is the temperature in KELVIN. Units , kJmol-1

Question 9

How do you convert between ºC and Kelvin?

Answer 9

ºC to Kelvin add 273

Kelvin to ºC subtract 273

Question 10

What do you need to watch out for?

Answer 10

△S⦵ is in Joules while △H⦵ is in kJ, so when doing the equation it really needs to be to get the answer in kJ
△G⦵ = △H -T(△S⦵ ÷ 1000)

Question 11

What do you do when they ask you to find the temperature at which the reaction is feasible?

Answer 11

Set △G = 0 and do T = △H ÷ △S where △S needs to be in kJmol-1

Question 12

What is special about a change in state?

Answer 12

△G = 0, therefore △H = T△S