C5: Thermodynamics

Question 1

what is the formula for calculating enthalpy change?

Answer 1

(change in) Hrxn= (change in)Hproducts - (change in)Hreactants

Question 2

what is the Hf of pure elements in their standard state?

Answer 2

0

Question 3

elements that are under standard state conditions have a change in H of ____

Answer 3

0

Question 4

• if you reverse a reaction, what happens in regard to the numerical value of change in H?
• what about if you multiply a rxn by a constant?

Answer 4

• the sign of the numerical value needs to be reversed
• you multiply change in H by the same constant

Question 5

if bonds are formed….
- energy is ____ (absorbed/released)
- change in H is ____ (greater than/less than) 0
- it is an ____ (endothermic/exothermic) rxn
- if bonds are broken, what are the answers to these questions?

Answer 5

• released
• less than
• exothermic
• absorbed; greater than; endothermic

Question 6

a +change in GFE is….
- favorable/ unfavorable
- spontaneous/ nonspontaneous
- occur without added energy?
- net effect?

Answer 6

-unfavorable
- nonspontaneous
- no
- reactant stays reactant

Question 7

a - change in GFE is….
- favorable/ unfavorable
- spontaneous/ nonspontaneous
- occur without added energy?
- net effect?

Answer 7

• favorable
• spontaneous
• yes
• reactant becomes product

Question 8

if change in GFE = 0, the rxn is ____

Answer 8

at equilibrium

Question 9

what is the 3rd law of thermodynamics?

Answer 9

at absolute zero, nothing moves

Question 10

for the following list, indicate which is related to kinetics (K) and which is related to thermodynamics (T):
- catalyst
- GFE (G)
- activation energy
- enthalpy (H)

Answer 10

• K
• T
• K
• T