Unit 5: Thermodynamics And Entropy

Question 1

Define Non-Spontaneous Reactions

Answer 1

Types of reactions that will not happen on their own; need an input of energy (will only happen with some external stimulus, like a lot of heat or a catalyst)

Question 2

Define Spontaneous Reactions

Answer 2

Reactions that will happen on their own (no input of energy needed)

Question 3

The reverse process of a spontaneous reaction is _____.

Answer 3

Non-Spontaneous

Question 4

Are all exothermic processes spontaneous?

Answer 4

NO

Question 5

Define Entropy

Answer 5

Entropy (S) is a measure of how dispersed the energy in a system is at a specific temperature. Some w/ high entropy has more possible states of freedom or existence.

Question 6

How will the reaction behave if DELTAH is positive?

Answer 6

Non-spontaneous

Question 7

How will the reaction behave if DELTAH is negative?

Answer 7

Spontaneous

Question 8

What is the 1st Law of thermodynamics?

Answer 8

When energy passes into or out of the system, the total energy is conserved; energy is neither created or destroyed: it simply transforms from one form to another.

Question 9

What is the 2nd Law Of thermodynamics?

Answer 9

All spontaneous processes cause (or are associated with) an increase in the entropy of the universe.

Question 10

Why do spontaneous processes increase the spontaneity of the universe?

Answer 10

Because “disordered states” are of much higher probability.

Question 11

Entropy essentially means _____

Answer 11

Disorder.

Question 12

Define Microstates

Answer 12

Microstates (W) describe the # of possible arrangements of a particular system. The more the Microstates, the higher the entropy.

Question 13

What is the equation for entropy and what does each variable stand for?

Answer 13

S= kb . LnW —-> kb= Boltzmann’s constant (1.38x10^-23J/K); W= accessible Microstates

Question 14

What does the 3rd law of thermodynamics state?

Answer 14

A perfect crystalline solid has an entropy of zero at absolute zero. This is because all particles have no freedom of motion and no kinetic energy.

Question 15

How does the entropy vary for different phases (generally speaking)?

Answer 15

S solid < S liquid <S gas

Question 16

How is entropy related to temperature, volume, and the # of particles present in a system?

Answer 16

It is DIRECTLY related to them.

Question 17

What is the equation for the change in entropy of the universe? Under what conditions is it positive/negative?

Answer 17

S Universe= S system+ S Surroundings; S University>0 —-> Spontaneous; S Univ<0 —-> Non-Spontaneous

Question 18

What are reversible processes? What is the equation for it?

Answer 18

A reversible process is when a final state can be brought back to its initial state, with no net energy lost from the system and surroundings.

DELTA S= q rev/T; q rev= reversible heat flow between system and surroundings

Question 19

What is the formula for calculating the entropy of a reaction?

Answer 19

Delta S rxn= sum of the moles of the products- sum of the moles of reactions

Question 20

What is the equation for Gibbs Free Energy?

Answer 20

DELTA G= DELTAH- TDELTAS

Question 21

What can we conclude when Delta G is less than 0? What about when it is greater than 0?

Answer 21

Less than 0 means spontaneous and exergonic.
Greater than 0 means non-spontaneous and endergonic.

Question 22

What happens in coupled reactions?

Answer 22

The energy released from Exergonic reactions can be used to drive endergonic reactions. This is through a net-spontaneous reaction.

Question 23

What is the equation for Delta S? How does low T and high T impact it?

Answer 23

Delta S= Q/T

Low T: heat given off will increase entropy a lot more (dispersal impacts low T surroundings).

High T: heat given off will decrease the entropy because the molecules surrounding the rxn are high in KE ( heat dispersed has low impact on surrounding molecules with high temp)

Question 24

What does the graph of S vs. T look like?

Answer 24

It is linear; increased temperature leads to an increased entropy.

Question 25

What is the idea of Gibbs Free Energy?

Answer 25

It is the available energy to do work.

Question 26

What is the equation for Gibbs Free Energy?

Answer 26

Delta G= DELTA H- T DELTA S

Question 27

What does the sign of the DELTA G tell us?

Answer 27

If it is negative, it is spontaneous; if it is positive, it is non-spontaneous.

Question 28

How does the sign of DELTA H impact the sign of DELTA G

Answer 28

In the case that the sign of DELTA H and DELTA S are different, whether or not DELTA G is positive or negative depends on the sign of the Delta H. If the sings of the DELTA H are in accordance with the sign of the DELTA S, plug numbers in.