Chapter 17: Thermodynamics

Question 1

What is the spontaneity of the process when the change in entropy of the system is greater than 0 and the change in entropy of the surroundings is greater than one?

Answer 1

The process is always spontaneous

Both positive no worry

Question 2

What is the spontaneity of the process when the change in entropy of the system is less than 0 and the change in entropy of the surroundings is greater than one?

Answer 2

Spontaneous if the absolute value of the change in entropy of the system is less than the absolute value of the change in entropy of the surrounding
Non-spontaneous if the absolute value of the change in entropy of the system is greater than the change in entropy of the surroundings
* Temperature of surrounding is greater than that of the system in an exothermic process (freezing)
water put in freezer

Question 3

What is the spontaneity of the process when the change in entropy of the system is greater than 0 and the change in entropy of the surroundings is less than one?

Answer 3

Spontaneous if the absolute change in entropy of the system is greater than the absolute change in entropy of the surroundings
Non-spontaneous if the absolute value of the change in entropy of the system is less than that of the surroundings.
*temperature of surrounding is greater than that of system in an endothermic process (melting)

Question 4

What is the spontaneity of the process when the change in entropy of the system is less than 0 and the change in entropy of the surroundings is less than one?

Answer 4

The process is always non-spontaneous

Both negative there is nothing you can do

Question 5

What is a spontaneous process?

Answer 5

A process that occurs without external intervention (air out of tire)
Disorder of energy

Question 6

What is a non-spontaneous process?

Answer 6

A process that only occurs if energy is continually added to the system (air into tire)
Order of energy

Question 7

What does spontaneity depend on?

Answer 7

The dispersion of energy, the entropy, that occurs during a process.

Question 8

What is the molecular motion across the phases? How does the increase or decrease of molecular motion relate to kinetic energy and entropy?

Answer 8

Solid: vibrational motion (not much motion)
Liquid: translational
Gas: translational & rotational
As molecular motion increases so does kinetic energy and entropy

Question 9

Define entropy:

Answer 9

The measure of how dispersed energy is in a system at a specific temperature.
The energy distribution affected by molecular motion and volume.

Question 10

What is the second law of thermodynamics?

Answer 10

The total entropy of the universe increases in any spontaneous energy.

Change in entropy of universe = change in entropy of system + change in entropy of surroundings.

Question 11

What is an isothermal process?

Answer 11

Reversible process{ a process that can be run in reverse and no net energy has flowed to system or surroundings. (ie flow of heat, q)

Question 12

What is the difference between H and q?

Answer 12

There is no difference between H and q. H is q for a certain process (i.e. melting or freezing)

Question 13

What is q rev and how does it relate to entropy?

Answer 13

It is the flow of heat in a reversible reaction. Change in entropy = q rev / Temperature

Question 14

At what temperature does all molecular motion cease and entropy equal zero?

Answer 14

At absolute zero

Question 15

What is the third law of thermodynamics?

Answer 15

The entropy of a perfect crystal is zero at absolute zero.

Question 16

What is the standard molar entropy?

Answer 16

S*, the absolute entropy of one mole of a substance in its standard state at 298K and one bar of pressure.

Calculated from measurement of molar heat capacities as a function of temperature

Question 17

How does entropy relate to the structure of a molecule?

Answer 17

Entropy increases with increasing complexity of structure.
(more bonds more opportunities for internal motion)
CH4–> CH3CH3 –> CH3CH2CH2CH3

Question 18

How do you calculate the entropy change for the system?

Answer 18

Change in standard molar entropy of a rxn = the sum of n products * molar entropy products - sum of n reactants * molar entropy reactants.

Question 19

What is Gibbs Free Energy?

Answer 19

(G) the Maximum energy released by a process occurring at constant temperature and pressure that is available to do useful work.

Question 20

How is G calculated from the change in entropy of the universe?

Answer 20

ASuni = ASsys + ASsurr
ASuni = ASsys - AHsys/T
-TASuni = - TASsys + AHsys
AG = AH - TAS
The change in Gibbs Free energy equals the negative temperature times the change in entropy of the universe.

Question 21

What are the driving forces that contribute to spontaneity?

Answer 21

The system experiences an increase in entropy: ASrxn > 0
The process is exothermic: AHrxn < 0

Question 22

What does the Gibbs free energy reaction relate?

Answer 22

It relates enthalpy, entropy, and temperature for a process.

Question 23

How is the change in standard molar Gibbs free energy calculated?

Answer 23

The change in standard molar Gibbs free energy of a reaction = the sum of the n product * the change in standard molar Gibbs free energy products - the sum of the n reactant * change in standard molar Gibbs free energy reactants

Question 24

What is free energy?

Answer 24

Energy available to do useful work

Question 25

What can the change in internal energy of a system be used for?

Answer 25

It can be used to perform work: AE = q + w

Question 26

How can thermodynamic efficiency be calculated?

Answer 26

(Work done) / (energy produced)

Question 27

What is the change in enthalpy is negative and the change in entropy is positive what is the change in G and what is the spontaneity of the system?

Answer 27

The change in G will always be less than zero and the reaction will be always spontaneous

Question 28

What is the change in enthalpy is negative and the change in entropy is negative what is the change in G and what is the spontaneity of the system?

Answer 28

The change in G will be less than zero at lower temperatures and the process will be spontaneous at lower temperatures--ice freezes at lower temperatures

Question 29

What is the change in enthalpy is positive and the change in entropy is positive what is the change in G and what is the spontaneity of the system?

Answer 29

The change in G will be less than zero at higher temperatures and the process will be spontaneous at higher temperatures. (Ice melt at higher temperatures)

Question 30

What is the change in enthalpy is positive and the change in entropy is negative what is the change in G and what is the spontaneity of the system?

Answer 30

The change in G will always be greater than zero. Process will never be spontaneous

Question 31

How is Q verses K related to AG?

Answer 31

Q=K AGrxn = 0, system is at equilibrium QK AGrxn > 0 the system will proceed spontaneously in the revers direction

Question 32

How are AG and K related?

Answer 32

AG < 0; K is large, favors products AG slightly < 0; K slightly favors products AG > 0; K << 1, favors reactants *May not be true in standard conditions*

Question 33

What will the slope of a reaction be if the reaction is exothermic, is endothermic?

Answer 33

Exothermic: positive slope (b/c AH -) Endothermic: negative slope (b/c AH +)

Question 34

What is the equation ln(K2/K1)=-AH*/R(1/T2-1/T1) used for?

Answer 34

To find initial and final temperatures.

Question 35

What does the degree symbol mean?

Answer 35

Standard conditions 298.15K