Module 4

Question 1

At standard conditions, determine if a reaction is spontaneous, if it is exothermic or endothermic,
and if it increases entropy. Know which data you need to determine this.

Answer 1

G
-useable energy gained or released by reaction
More negative -> release a lot of energy
More positive -> needs a lot of energy to initiate

S
Internal disorder of a substance
negative: Decrease in entropy -> less disorder
positive entropy: spontaneous
low entropy ->low disorder
high entropy -> high disorder

H
Positive: endothermic, system absorbs energy
Negative: exothermic, system releases energy

Question 2

What is unstable, metastable, and stable as it pertains to gibbs energy?

Answer 2

Unstable -> needs decrease in energy
Metastable -> could release more energy but needs activation energy to get started
Stable -> has minimal gibbs free energy

Question 3

What is the common ion effect?
Le chateliers principle

Answer 3

If a common ion already exists in solution, the total amount of a compound that can dissolve will decrease

System will proceed in the direction to counteract change

Question 4

Explain why some spontaneous reactions do not appear to proceed forward very rapidly at Earth
surface conditions. Provide a geochemical example

Answer 4

High activation energy
2) Reactions occur at very slow rate
Graphite to diamond has a very large energy barrier

Question 5

What does k tell you about solubility?

What does k mean for a weathering reaction?

Answer 5

Smaller k -> more insoluble

Large k -> reaction is happening readily
small k -> mineral being weathered is quite stable

Question 6

determine rate order for reaction
-what is rate law, rate constant, know units of k

Answer 6

Zeroth order: reaction rate constant
k = mol L–1 s–1

 First order: rate depends on [reactant]
s-1

 Second order: rate depends on [reactant]2
1/(M·s)