5.2.2 Enthalpy and Entropy

Question 1

Define entropy and its units

Answer 1

Measure of dispersal of energy within a chemical system. J K-1 mol-1

Question 2

Greater entropy means what?

Answer 2

Greater disorder

Question 3

What are some examples of things that increase entropy?

Answer 3

Increase in temperature
Change of state ( solid to liquid to gas)
Dissolving of something
Gas production

Question 4

What is standard entropy change?

Answer 4

Entropy of one mole of a substance under standard conditions, always positive

Question 5

What occurs during state changes (solid-> liquid -> gas) in terms of entropy and temp?

Answer 5

Temp stays the same but S increases since more freedom

Question 6

How do you calculate standard entropy change?

Answer 6

Entropy of products - entropy of reactants

Question 7

What is feasibility?

Answer 7

Energetically, can the reaction happen?

Question 8

What is the equation for free energy change? What does it have to be to be feasible?

Answer 8

dG = dH- TdS. Temp in Kelvin. G has to be less than 0.

Question 9

What is the limitation to feasibility?

Answer 9

A reaction may not be kinetically feasible ( e.g. very high activation energy)

Question 10

For the condensation of ammonia gas, what are the signs of dH and dS?

Answer 10

dH = negative
dS = negative

Question 11

Which row has signs for dH and dS for a reaction that is feasible at high temperatures but NOT feasible at low temperatures?

Answer 11

DH = +
DS = +