CHEM 203: Thermodynamics Part 2

What is the second law of thermodynamics?

What is the second law of thermodynamics?

• heat always moves from hotter objects to cooler objects, unless energy is supplied to cause the reverse to occur

• for any spontaneous process the entropy of the universe must always increase

What is a spontaneous process?

a process that occurs on its own (does not refer to the rate of reaction)

What determines the direction of a spontaneous process?

the entropy change

What is entropy?

the dispersal of matter and energy (sometimes defined as a measure of the “disorder”)

At equilibrium entropy of the universe must be _________, and change in entropy of the universe must be ___.

• at a maximum

• 0

Entropy is a _______ function and is ___________, meaning that it depends on _________________.

• state

• extensive

• the amount of substance

What is the 2nd law of thermodynamics?

For any spontaneous process the entropy of the universe must always increase (change always occurs in the direction of maximal probability).

How does volume change of a gas affect entropy?

entropy increases with volume because there are more possible positions for each particle (disorder increases)

How does temperature change affect entropy?

entropy increases with temperature because there are more possible energies for each particle (disorder increases)

Since S increases with T, this implies that in an exothermic reaction heat flows ________ of the system and the entropy of the surroundings _____________.

• out

• increases

In which phase is entropy the lowest? In which phase is entropy the highest?

• lowest → solid (most ordered)

• highest → gas (most disordered)

How does mixing of gases affect entropy?

gases always mix, so entropy will always increase with mixing

How does number of moles affect entropy?

increasing the number of moles increases entropy

What is the 3rd law of thermodynamics?

The entropy of a perfect crystalline solid at 0 K is defined to be 0 J/K

What is standard entropy?

The entropy of 1 mole of a substance at standard state conditions

At constant temperature and pressure, delta G equals?

delta G = delta H - T * delta S

If delta G is negative, the forward process is ____________

spontaneous

If delta G is positive, the forward process is _____________

non-spontaneous

If delta G is 0, the process is _____________

at equilibrium

What does delta G represent?

the maximum energy available to do work

A system at equilibrium can do no ________

work

Fill out this table

What does exergonic mean? What does endergonic mean?

• exergonic → -delta G

• endergonic → +delta G

For a system at equilibrium at constant temperature and pressure delta G equals ____

0

What are standard free energies of formation?

the value for the formation of 1 mole of a substance from the most stable forms of its elements

At standard state conditions, if free energy change is less than 0, K is ____________

greater than 1

At standard state conditions, if free energy change is greater than 0, K is ___________

less than 1

At non-standard state conditions, if free energy change is less than 0, then Q is ________ than K and the reaction is ______________

• less

• spontaneous

At non-standard state conditions, if free energy change is greater than 0, then Q is ________ than K and the reaction is ______________

• greater

• non-spontaneous