Chapter 19 and 20

Question 1

Chemical reactions may be classified as _________ and _________ regarding to their spontaneity

Answer 1

Spontaneous and non-spontaneous

Question 2

Spontaneity and rate are interchangeable terms

Answer 2

False, they are not the same

Question 3

The use of a catalyst can turn a non-spontaneous reaction into spontaneous reaction as long as the catalyst is a metal.

Answer 3

False, catalysts typically do not change the rate of non-spontaneous reactions. They can cause an increase on the rate of spontaneous reactions while also being consumed in the reaction

Question 4

A non-spontaneous can’t be made spontaneous at all.

Answer 4

False, a non-spontaneous reaction can be turned spontaneous by coupling it to another process that is spontaneous or by supplying energy from an eternal source

Question 5

According to the second law of thermodynamics, we expect:
Exothermic reactions to be ________ and endothermic reactions to be _____________

Answer 5

Spontaneous (give off energy) and non-spontaneous (absorb energy)

Question 6

Enthalpy and entropy are important criteria to define spontaneous change.

Answer 6

Although enthalpy might give us a clue about a reaction’s spontaneity, it is not the criteria for it.

Question 7

What is entropy?

Answer 7

It is a thermodynamic function that increases with the number of energetically equivalent ways to arrange components of a system to achieve a particular state.

Question 8

What does W represents in the entropy definition?

Answer 8

The number of energetically equivalent ways to arrange the components of the system

Question 9

The dissolution of NaCl(s) in an aqueous medium can be described as spontaneous, why?

Answer 9

Because the orderly arranged ions of NaCl(s) will become disorderly arranged in solution.

Question 10

What does the 2nd law of thermodynamics state?

Answer 10

That a chemical process will proceed in a direction that increases the entropy of the universe.

Question 11

Entropy is maximized when…

Answer 11

Energy dispersal is maximized

Question 12

How can we rank the difference in entropy of different states?

Answer 12

The entropy of solid < the entropy of liquid < the entropy of gas

Question 13

Delta S is also positive in a reaction in which the moles of gas…

Answer 13

…increase

Question 14

How can we explain condensation (g->l) as being spontaneous?

Answer 14

Because even though the entropy change in unfavorable, condensation is an exothermic process, therefore a lot of heat is released by the surroundings, which compensates for the randomness of the condensation.

Question 15

At ________ the decrease in entropy of the system is controlled by the _______ in the entropy of the surroundings resulting in a positive delta S and a _________ process.

Answer 15

Low temp, large increase, spontaneous

Question 16

At ________ the decrease in entropy of the system does not overcome by the _______ in the entropy of the surroundings resulting in a negative delta S and a _________ process.

Answer 16

High temp, increase, nonspontaneous

Question 17

What can we infer from a process with a -ΔH?

Answer 17

That the process emits heat to the surroundings, therefore it increases the entropy of the surroundings.

Question 18

What is Gibbs free energy?

Answer 18

It is the maximum amount of work energy that can be released to the surroundings by a system for a constant temp and pressure

Question 19

A reaction has a positive delta H and a negative delta S. What can you conclude about the spontaneity of the reaction?

Answer 19

Delta G will be positive, therefore the reaction will be nonspontaneous at all temperatures

Question 20

What is a spontaneous process?

Answer 20

A spontaneous process is one that occurs without ongoing outside intervention. An example of a spontaneous process is the expansion of an ideal gas into a vacuum

Question 21

What happens to the entropy of a sample of matter when it changes state from a solid to a liquid?

Answer 21

Increases

Question 22

What happens to the entropy of a sample of matter when it changes state from a liquid to a gas?

Answer 22

Increases

Question 23

How can we determine if the entropy of a reaction is increasing or decreasing, without performing calculations?

Answer 23

If there is a gas originating from a solid, or a liquid from a sold, which indicates that the entropy is increasing

Question 24

Which process is expected to have an increase in entropy?

Iron rusting

Precipitation of BaSO4BaSO4 from mixing solutions of BaCl2BaCl2 and Na2SO4Na2SO4

Formation of liquid water from hydrogen and oxygen gas.

Decomposition of N2O4 gas to NO2 gas

Answer 24

Decomposition of N2O4 gas to NO2 gas, as when the equation is balanced we have one mole of the N2O4 gas and 2 moles of the NO2 gas, therefore increasing the number of moles available

Question 25

What is the standard state for a gas?

Answer 25

Pure gas at 1 atm

Question 26

What is the standard state for a liquid or a solid?

Answer 26

Pure substance in its most stable form @ 1 atm and a particular temp.

Question 27

What is the standard state for a solution?

Answer 27

1M concentration

Question 28

What is the standard entropy for a reaction?

Answer 28

The change in entropy for a process in which all reactants and products are in their standard states.

Question 29

What is the absolute entropy of a substance?

Answer 29

It is the amount of energy it has due to its dispersion of energy through its particles

Question 30

What is the entropy of a perfect crystal at 0K?

Answer 30

Zero

Question 31

The standard molar entropy is an example of what type of property?

Answer 31

Extensive property

Question 32

What is the relationship between molar mass and entropy? Why?

Answer 32

They are directly proportional, therefore the larger the molar mass, the larger the entropy. Because heavier atoms are closer together allowing for the dispersal of energy.

Question 33

What are allotropes?

Answer 33

They are elements that can exist in two or more forms in the same state of matter

Question 34

How do we measure for the entropy of allotropes?

Answer 34

The less constrained the structure of the allotrope is, the larger the entropy. In the case of carbon (C), the layers in graphite are not bonded together as the layers in a diamond

Question 35

Entropy generally ________ with increasing molecular complexity

Answer 35

Increases. Generally molecules tend to have more freedom to store the atoms (entropy) than free atoms

Question 36

Dissolution results in an increase on the entropy. Why?

Answer 36

Because when molecules dissolve in water, they release the energy that was concentrated within the crystal. The greater the dispersal of energy, the greater the entropy.

Question 37

Define electrical current

Answer 37

Flow of electrons through a wire of aqueous solution of ions

Question 38

Define voltaic cells

Answer 38

Electrochemical cell that produces electrical current from a spontaneous chemical reaction

Question 39

Define electrolytic cell

Answer 39

It consumes electrical current to drive a nonspontaneous chemical reaction

Question 40

Why are redox reactions able to create an electric current under the right conditions?

Answer 40

Because redox reactions involve the transfer of electrons from one substance to another

Question 41

\_\_\_\_\_\_\_\_\_ is the electrode where oxidation occurs

Answer 41

Anode

Question 42

\_\_\_\_\_\_\_ is the electrode where reduction occurs

Answer 42

Cathode

Question 43

\_\_\_\_\_\_\_\_\_ will start building up on the anode side and _______ will start building up in the cathode side.

Answer 43

Cations, anions

Question 44

Why is the salt bridge important?

Answer 44

The salt bridge allows the passage of electrolytes that neutralize the charge buildup in the solutions.

Question 45

When referring to the voltaic cell of Zn and Cu, we can say that Zn dissolves in the Cu sln.

Answer 45

False, Zn reacts with it.

Question 46

What causes the transfer of electrons in a Zn/Cu voltaic cell?

Answer 46

The tendency of Zn to transfer electrons to Cu

Question 47

What is the driving force for an electrical current?

Answer 47

Potential differences

Question 48

What is the potential difference?

Answer 48

The measurement of the difference in potential energy usually given in J/C, It is also referred to as the electromotive force

Question 49

What does the cell potential in a voltaic cell measure?

Answer 49

The overall tendency of the redox reaction to occur spontaneously. Therefore, the lower the Ecell, the lower tendency for the reaction to occut

Question 50

In a voltaic cell, in which direction do electrons flow?

Answer 50

From higher potential energy to lower potential energy

Question 51

What is the standard electrode potential?

Answer 51

The potential (or voltage) of a half cell under the standard conditions

Question 52

The more _______ the electrode potential, the greater the potential energy of an electron to undergo oxidation

Answer 52

Negative

Question 53

What does a positive half-cell potential mean?

Answer 53

That the species has a greater tendency than H to undergo reduction

Question 54

What does a negative cell potential mean?

Answer 54

That the species has a greater tendency than H to undergo oxidation

Question 55

An electrode has a negative electrode potential. Which statement is correct regarding the potential energy of an electron at this electrode?

Answer 55

An electron at this electrode has a higher potential energy than it has at a standard hydrogen electrode.

Question 56

What is the second law of thermodynamics?

Answer 56

The second law of thermodynamics states that the total entropy of an isolated system (the thermal energy per unit temperature that is unavailable for doing useful work) can never decrease.

Question 57

What is the third law of thermodynamics?

Answer 57

The Third Law of thermodynamics states that the entropy of a pure substance in a perfect crystalline state at zero temperature is zero.