2.3 Entropy & Spontaneous Change

Question 1

What is a spontaneous process?

Answer 1

process occurring in the absence of any ongoing outside intervention

Question 2

In what direction do spontaneous reactions occur?

Answer 2

in one direction
–> reactions are non spontaneous in the reverse direction

Question 3

Does exothermic or endothermic reactions occur spontaneously?

Answer 3

either

Question 4

What is entropy (S)?

Answer 4

MEASURE OF THE RANDOMNESS OF A SYSTEM

Question 5

How does entropy increase?

Answer 5

higher number of possible arrangements (mixing possibilities
–> mixing is a spontaneous reaction
∆S > 0

Question 6

How are reaction rate and spontaneity related?

Answer 6

they are not; being spontaneous has nothing to do with speed

Question 7

Is entropy a state function?

Answer 7

Yes! ∆S = S(final) - S(initial)

Question 8

Does nature favour high entropy?

Answer 8

yes, nature favours more disorder

Question 9

How can low entropy be produced?

Answer 9

adding energy to create order
–> will create entropy somewhere else

Question 10

What impacts entropy?

Answer 10

temperature and phase change
increase temp increase entropy
S(gas) > S(liquid) > S(solid)

Question 11

What impacts entropy more: temperature or state change?

Answer 11

state change

Question 12

Is the entropy of fusion or vaporization larger?

Answer 12

vaporization

Question 13

Why does entropy increase with temperature?

Answer 13

measuring kinetic energy of molecular motion: translational, vibrational, and rotational motion

Question 14

Is there motion at absolute zero? (0ºK)?

Answer 14

no translational or rotational motion, but atoms have vibrational

Question 15

What is zero-point vibrational energy?

Answer 15

explains vibrational motion at absolute zero
- as atoms are warmed, molecules in the solid begin to vibrate more = increase in atomic/molecular positions = increase in entropy

Question 16

How can chemical reactions affect entropy?

Answer 16

if section involves 1+ reactants or products in the gas phase

Question 17

How does number of molecules impact entropy>

Answer 17

increase # of molecules in gas phase = increase entropy because two moles of gas particles have more freedom of motion = more possible arrangements

Question 18

What is the 2nd law of thermodynamics?

Answer 18

every spontaneous process increases the entropy of the universe
∆S(Universe) = ∆S(sys) + ∆S(surr) > 0

Question 19

How can you determine if a process is spontaneous?

Answer 19

determine if the process is associated with an overall increase of entropy to the universe

Question 20

Is it possible for a spontaneous process to have ∆S (sys) < 0?

Answer 20

Yes, if ∆S(surr) > 0 is very large

Question 21

What is the 3rd law of thermodynamics?

Answer 21

entropy of a perfectly ordered crystalline solid is defined to be zero at a temperature of absolute zero

Question 22

What is the implication of the 3rd law?

Answer 22

absolute entropies can be measured because there is a definition of zero entropy

Question 23

What is standard molar entropy (Sº)?

Answer 23

absolute entropy of 1 mole of a substance in its standard state

J/mol*K

Question 24

How can ∆Sº be calculated?

Answer 24

∑Sº (products) - ∑Sº (reactants)

Question 25

What is the relationship between number of atoms and entropy?

Answer 25

increasing number of atoms = more motion = more possible arrangements = larger molecules = increase entropy

Ex. C3H8 > C2H6 > C2H4 > CH4