Unit 11- Spontaneity, Entropy, Free Energy, and Electrochemistry

Question 1

Historically, _____ processes were thought to correspond to exothermic processes.

Answer 1

Spontaneous

Question 2

Define Spontaneity and its characteristics

Answer 2

A process that occurs without outside intervention (ex. continuously supplying heat)- can be fast or slow.

Question 3

Often, _____ reactions are spontaneous; give a few examples.

Answer 3

Exothermic- Nails rusting when exposed to the environment- Ice spontaneously freezing at a temperature below 0C- Wood burning to produce CO2 and H2O

Question 4

_____ processes can also be spontaneous; give an example.

Answer 4

Endothermic- Ice spontaneously melting at a temperature above 0C.

Question 5

What is the driving force in endothermic processes that are spontaneous?

Answer 5

Increase in entropy.

Question 6

Define Entropy

Answer 6

Molecular randomness or disorder- the number of positions or energy levels at which a system can exist.

Question 7

In a disordered state, there is _____ and _____ (ex. _____); in an ordered state, there is _____ and _____ (ex. _____)

Answer 7

High Probability- High Entropy- Gases expand to fill space uniformly- Low probability- Low entropy- Rigid Solid

Question 8

Entropy tends to _____ as _____.

Answer 8

Increase- More available positional states are filled.

Question 9

What is the symbol for entropy?

Answer 9

S

Question 10

List the general guidelines regarding entropy.

Answer 10

1) S Solid

Question 11

How does pressure impact entropy?

Answer 11

The lower the pressure, the higher the entropy. (INVERSE)

Question 12

List everything about the Second Law of Thermodynamics.

Answer 12

The universe tends towards disorder (entropy of a closed system tends to increase).

If DeltaS of Universe is greater than 0, then the reaction is spontaneous.
If DeltaS of Universe is equal to 0, then the system is at equilibrium
If DeltaS of Universe is less than 0, then the reaction is not spontaneous in that direction… it is in the opposite direction.

DeltaS of Surroundings is positive for an exothermic process —> heat causes randomness in surroundings to increase.

Delta S of Surroundings is negative for an endothermic process.

The magnitude is dependent on temperature. There is a greater impact on the entropy of the surroundings if the temperature is lower.

Delta S of Surroundings= -DeltaH/T

Question 13

List everything about the Third Law of Thermodynamics.

Answer 13

Entropy of a perfect crystal at absolute zero is zero.

S at Standard State—> entropy gained by converting a substance from a perfect crystal at 0 K to standard conditions.

DeltaS Standard of Reaction= DeltaS System

Delta S Standard of Reaction= Sum of the moles of product times the standard entropy of product- sum of the moles of reactant times the standard entropy of reactant. (Entropy Products- Entropy Reactants)

Question 14

List everything about Gibb’s Free Energy.

Answer 14

Energy available to do work.

DeltaG Standard of Reaction= Sum of the moles of product times the standard G of the products - sum of the moles of reactant times the standard G of the reactants. (G Products- G Reactants)

If DeltaG is negative, the reaction is spontaneous
If DeltaG is zero, the reaction is at equilibrium
If Delta G is positive, the reaction is nonspontaneous

Reactions at a constant T and P proceed in a direction so as to decrease the free energy of the system.

DeltaG Standard= Delta H Standard- T DeltaS Standard

Factors that favor a (-) value of Delta G: 1) Negative value of DeltaH 2) Positive value of DeltaS 3) Temperature dependent if H and S are the same sign.

DeltaG Standard= -RT ln(k)
Delta G= DeltaG Standard+ RT ln (Q)

Question 15

When things lead to a reaction being spontaneous, we call it _____.

Answer 15

Thermodynamically Favorable.

Question 16

What are the standard state conditions?

Answer 16

1atm- 1M- 25 Degrees Celsius

Question 17

For galvanic cells, the cell potential always has to be _____

Answer 17

Positive

Question 18

In galvanic cells, chemical energy—> _____

Answer 18

Electrical Energy

Question 19

E Standard Cell= _____

Answer 19

Cell Potential—>Electron Active Force—> Volts (J/C) which is joules over coulomb.

Question 20

Whenever you flip a half reaction, you must _____.

Answer 20

Change the sign of the cell potential.

Question 21

Oxidation occurs at the _____ and reduction occurs at the _____.

Answer 21

Anode-Cathode (OARC) —> Anode: e- away , Cathode: e- towards

Question 22

When using line notation, the _____ comes first and the _____ comes second.

Answer 22

Anode, Cathode

Question 23

Because all of the half-reactions are listed as reduction half-reactions, _____ both the sign and the reaction for the oxidation half-reaction.

Answer 23

Flip.

Question 24

Standard reduction potentials are _____. DO NOT _____ by coefficients.

Answer 24

Intensive- Multiply

Question 25

A cell will always run spontaneously in the direction of _____.

Answer 25

Positive cell potential.

Question 26

DeltaG Standard=

Answer 26

-nFE Standard of Cell; n= moles of electrons transferred in balanced redox reaction, F= 96485 C/ mol e- , E Cell= Volts—> same thing as J/C

Question 27

What is the Nernst Equation?

Answer 27

E Cell= E Standard Cell - (RT/nF) (lnQ)

Question 28

What is the meaning of oxidized?

Answer 28

When the oxidation number of a substance increases.

Question 29

What is the meaning of reduced?

Answer 29

When the oxidation number of a substance decreases.

Question 30

What are the steps in balancing a redox reaction in an acid?

Answer 30

1) Determine oxidized/reduced. Split into half-reactions.
2) Balance elements excluding oxygen and hydrogen.
3) Balance oxygen using water.
4) Balance hydrogen using H+.
5) Balance charge using electrons.
6) Balance electrons if necessary by multiplying half reactions by an integer.
7) Add half-reactions, cancel species, and check.

Question 31

What are the steps in balancing a redox reaction in a base?

Answer 31

1) Determine oxidized/reduced. Split into half-reactions.
2) Balance elements excluding oxygen and hydrogen.
3) Balance oxygen using water.
4) Balance hydrogen using H+
5) Add OH- to both sides to cancel H+. Combine OH- and H+ to form water. Simplify if necessary.
6) Balance charges using electrons.
7) Balance electrons if necessary by multiplying half-reactions by an integer.
8) Add half-reactions, cancel species, and check.

Question 32

Oxidizing Agents are _____.

Answer 32

Reduced/ lose O.

Question 33

Reducing Agents are _____.

Answer 33

Oxidized/ gain O.

Question 34

What are the common oxidizing agents and what do they form?

Answer 34

MnO4- in acidic solution —> Mn2+
MnO2 in acidic solution —> Mn2+
MnO4- in neutral/basic solution —> MnO2
Cr2O7 2- in acidic solution —> Cr3+

Question 35

What is the purpose of the Salt Bridge?

Answer 35

It balances charges.

Question 36

How do you know which ion from the salt bridge goes where?

Answer 36

The positive ion always goes to the cathode and the negative ion always goes to the anode.

Question 37

What are the steps in drawing a galvanic cell?

Answer 37

1) Draw two beakers
2) Draw a metal piece in each one, draw waves (water) in each one, and connect both metal pieces to the voltmeter.
3) Draw a salt bridge that goes into both beakers.
4) Find out which species is oxidized/reduced; then, based off of that, name each beaker cathode and anode respectively.
5) Draw the direction of the travel of the electrons in the voltmeter and the direction of the travel of the ions in the salt bridge.
6) Label the metal with its symbol and make sure it’s solid and label the water or solution with the aqueous form of the ion.
7) Finally, draw an arrow from the metal to the ion at the anode and draw an arrow from the ion to the metal at the cathode.

Question 38

What are the units of A?

Answer 38

Coulombs/Seconds