CHEM 203: Thermodynamics Part 2

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What is the second law of thermodynamics?

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1

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

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2

What is a spontaneous process?

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

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3

What determines the direction of a spontaneous process?

the entropy change

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4

What is entropy?

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

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5

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

  • at a maximum

  • 0

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6

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

  • state

  • extensive

  • the amount of substance

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7

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).

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8

How does volume change of a gas affect entropy?

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

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9

How does temperature change affect entropy?

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

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10

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

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11

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

  • lowest → solid (most ordered)

  • highest → gas (most disordered)

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12

How does mixing of gases affect entropy?

gases always mix, so entropy will always increase with mixing

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13

How does number of moles affect entropy?

increasing the number of moles increases entropy

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14

What is the 3rd law of thermodynamics?

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

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15

What is standard entropy?

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

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16

At constant temperature and pressure, delta G equals?

delta G = delta H - T * delta S

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17

If delta G is negative, the forward process is ____________

spontaneous

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18

If delta G is positive, the forward process is _____________

non-spontaneous

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19

If delta G is 0, the process is _____________

at equilibrium

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20

What does delta G represent?

the maximum energy available to do work

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21

A system at equilibrium can do no ________

work

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22
<p>Fill out this table</p>

Fill out this table

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23

What does exergonic mean? What does endergonic mean?

  • exergonic → -delta G

  • endergonic → +delta G

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24

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

0

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25

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

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26

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

greater than 1

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27

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

less than 1

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28

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

  • less

  • spontaneous

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29

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

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