Chapter 2: 2.3 Entropy and Spontaneous Change

Question 1

True or False:

Enthalpy along cannot predict reaction spontaneity

Answer 1

True

Question 2

Define:

Spontaneous process

Answer 2

A process that occurs in the absence of any ongoing outside intervention

Question 3

Why is the 1st Law of Thermodynamics insufficient?

Answer 3

Sometimes exothermic reactions will not occur spontaneously, and sometimes endothermic reactions will occur spontaneously

Question 4

What do you have to consider in order to determine whether a process will occur spontaneously?

Answer 4

Entropy

Question 5

Define:

Entropy

Answer 5

A measure of the randomness of a system

Question 6

What does a higher entropy mean?

Answer 6

There is a higher number of possible arrangements of a system

Question 7

True or False:

Mixing is a spontaneous process

Answer 7

True, as mixing increases the entropy of a system

Question 8

True or False:

Spontaneous reactions are fast

Answer 8

False, processes that occur spontaneously are not necessarily fast

Question 9

State:

Notation for Entropy and Entropy Change

Answer 9

S and ΔS

Question 10

State the formula for:

Entropy change

Answer 10

ΔS = S (final) - S (initial)

Question 11

What does ΔS > 0 and ΔS < 0?

Answer 11

• ΔS > 0 corresponds to an increase in the number of possible arrangements
• ΔS < 0 corresponds to a decrease

Question 12

What is the effect on entropy when heat is added to the system?

Answer 12

Entropy increases with temperature

Question 13

What processes increase entropy (temperature-wise)?

Answer 13

Vapourization, melting, sublimation
(S gas > S liquid > S solid)

Question 14

What is the 3rd Law of Thermodynamics?

Answer 14

The entropy of a perfect crystal solid is defined as zero at 0K

Question 15

Entropy increases with temperature, which is measure of what?

Answer 15

Kinetic energy of molecular motion in the system (translational, vibrational, rotational)

Question 16

True or False:

At temperature of absolute zero, the substance has no motion

Answer 16

Not necessarily. Due to quantum effect known as zero-point vibrational energy, atoms are still vibrating (but no translational or rotational motion)

Question 17

How do chemical reactions affect entropy?

Answer 17

Increasing the number of molecules in the gas-phase increases entropy, as can many other factors

Question 17

State:

2nd Law of Thermodynamics

Answer 17

Every spontaneous process increases the entropy of the universe

Question 18

State the formula for:

2nd Law of Thermodynamics

Answer 18

• ΔS univ > 0
• ΔS univ = ΔS sys + ΔS surr > 0

Question 19

What notation and units are standard molar entropies typically reported in?

Answer 19

• S^o
• J/mol K
• Refers to standard states, where all gases have partial pressures of 1 atm and all species in solution have concentration of 1 M
• Listed values usually at 25 degrees Celsius

Question 20

State the formula for:

Standard entropy change (ΔS^o)

Answer 20

ΔS^o = ΣS^o (products) - ΣS^o (reactants)