AP Chemistry: Unit 9 Test Review

What is the dispersal of matter or energy in a sample of matter referred to as?

Entropy

Unit 9.1 - Introduction to Entropy

Unit 9.1 - Introduction to Entropy

When matter becomes more dispersed what happens to entropy?

Entropy increases(think how gas molecules are more dispersed than solid molecules).

Entropy of a gas increases when there is an increase in what? why?

When there is an increase in volume because the molecules can move within a larger space at the same speed.

According to the kinetic molecular theory, the distribution of kinetic energy among the particles of a gas broadens as what increases?

Temperature

For unit 9.1 know how to explain why entropy increases/decreases especially when given a diagram of molecules and their dispersion. Also, be able to predict the change in entropy based on the number of gas molecules on either side of the reaction.

For unit 9.1 know how to explain why entropy increases/decreases especially when given a diagram of molecules and their dispersion. Also, be able to predict the change in entropy based on the number of gas molecules on either side of the reaction.

Unit 9.2 - Absolute Entropy and Entropy Change

Unit 9.2 - Absolute Entropy and Entropy Change

The entropy change for a process can be calculated from the absolute entropies of the species involved when?

Before and after the process occurs

What are the units for entropy?

J/K*mol

For unit 9.2 know how to find the change in absolute entropy when given the absolute entropy value for each product and reactant.

For unit 9.2 know how to find the change in absolute entropy when given the absolute entropy value for each product and reactant.

What is the formula to find the absolute change in entropy?

ΔS°reaction = ΣS°products - ΣS°reactants

Unit 9.3 - Gibbs Free Energy and Thermodynamic Favorability

Unit 9.3 - Gibbs Free Energy and Thermodynamic Favorability

It is known that chemical reactants proceed until equilibrium is reached, however, some favor what?

Some favor the reactants and some favor the products

What describes whether a reaction is thermodynamically favorable or unfavorable?

The change in Gibbs Free Energy, ΔG

Changes that are thermodynamically favorable proceed to equilibrium without what?

external intervention

True/False - Since a reaction is favorable it happens quickly

False - some favorable reactions still happen slowly

What does this symbol mean, ΔG°?

The Gibbs free energy change for a chemical process in which all reactants and products are in a standard state(pure substances, 1.0M aqueous solutions, 1atm gases).

Even if the Gibbs free energy is less than zero under some conditions, aka not at standard state, does not imply that ΔG° is what?

negative and vice versa

The standard Gibbs free energy change for a physical or chemical process may be determined from what?

The standard Gibbs free energy of formation of the reactants and products.

When the ΔG° for a process is less than 0, it is said to be what?

Thermodynamically favored

What is the equation for the standard Gibbs free energy of formation when given the standard Gibbs free energy of formation of the products and reactants?

ΔG°reaction = ΣG°products - ΣG°reactants

If entropy and enthalpy values can be predicted or determined by a given temperature, then the standard Gibbs free energy change can be calculated directly by what equation?

ΔG° = ΔH° - TΔS°

When the ΔH° is negative and the ΔS° is positive then the ΔG° is favored at what temperatures?

All temperatures

When the ΔH° is positive and the ΔS° is negative then the ΔG° is favored at what temperatures?

No temperatures

When the ΔH° is negative and the ΔS° is negative then the ΔG° is favored at what temperatures?

Low temperatures

When the ΔH° is positive and the ΔS° is positive then the ΔG° is favored at what temperatures?

High temperatures

Unit 9.4 - Thermodynamic and Kinetic Control

Unit 9.4 - Thermodynamic and Kinetic Control

For unit 9.3 know how to calculate standard Gibbs free energy of formation either through the standard Gibbs free energy of formation from the products and reactants or when given the change in entropy and enthalpy at a certain temperature. Also, know how to PREDICT Gibbs Free Energy when given a change in entropy and enthalpy. Lastly, know when a reaction is thermodynamically favorable(when the ΔG° is less than 0).

For unit 9.3 know how to calculate standard Gibbs free energy of formation either through the standard Gibbs free energy of formation from the products and reactants or when given the change in entropy and enthalpy at a certain temperature. Also, know how to PREDICT Gibbs Free Energy when given a change in entropy and enthalpy. Lastly, know when a reaction is thermodynamically favorable(when the ΔG° is less than 0).

Process that are favorable(ΔG° is negative) but don't appear to make products at measurable rates are said to be under what?

"Kinetic Control" aka they have a large activation energy

Just because a process seems to occur slowly or does not seem to occur at all does NOT mean that the process is at what?

equilibrium

For unit 9.4 be able to explain why a thermodynamically favorable reaction(ΔG° is negative) is not seeming to make products(because the process is under kinetic control and has a high activation energy.

For unit 9.4 be able to explain why a thermodynamically favorable reaction(ΔG° is negative) is not seeming to make products(because the process is under kinetic control and has a high activation energy.

Unit 9.5 - Free energy and Equilibrium

Unit 9.5 - Free energy and Equilibrium

The phrase "thermodynamically favored" (ΔG° is negative) means that what side of the reaction is favored at equilibrium?

The products are favored at equilibrium(k>1)

At equilibrium, there is no net change in the concentrations of the products or reactants, therefore, the ΔG° can be used to calculate/predict the equilibrium constant via what equation?

ΔG° = -RTln(k)

When the ΔG° is negative, K is _________ than 1 and the reaction favors the ___________.

greater; products

When the ΔG° is positive, K is __________ than 1 and the reaction favors the ____________.

less, reactants

For unit 9.5 understand the relationship between ΔG° and K. Also, know how to use the formula ΔG° = -RTln(k) to find the exact value of the equilibrium constant. Lastly, understand that when the reaction favors reactants over products the change in enthalpy is negative due to the reaction favoring the reactants(and a negative enthalpy means the energy is being added to the reactants side - exothermic).

For unit 9.5 understand the relationship between ΔG° and K. Also, know how to use the formula ΔG° = -RTln(k) to find the exact value of the equilibrium constant. Lastly, understand that when the reaction favors reactants over products the change in enthalpy is negative due to the reaction favoring the reactants(and a negative enthalpy means the energy is being added to the reactants side - exothermic).

Unit 9.6 - Coupled Reactions

Unit 9.6 - Coupled Reactions

Two reactions that share a common intermediate and have a power source are said to be what?

Coupled

In addition to a common intermediate and a power source, the sum of the ΔG of the coupled reactions needs to be what?

negative

When two reactions are coupled, you need to make sure to balance them which also means multiplying the Gibbs Free Energy value of the reaction that needs to be coupled.

When two reactions are coupled, you need to make sure to balance them which also means multiplying the Gibbs Free Energy value of the reaction that needs to be coupled.

In order to find the ΔG° of a coupled reaction, you need to _______ the balanced coupled reactions' ΔG together.

add

For unit 9.6 be able to find the ΔG° of coupled reactions and explain why they are able to be coupled(intermediate, power, source and the sum of the ΔG is negative).

For unit 9.6 be able to find the ΔG° of coupled reactions and explain why they are able to be coupled(intermediate, power source, and the sum of the ΔG is negative).

Unit 9.7 - Galvanic(Voltaic) and Electrolytic Cells

Unit 9.7 - Galvanic(Voltaic) and Electrolytic Cells

What is a device that can convert the energy released by a thermodynamically favorable redox reaction to electrical energy, or one that, conversely, can use electrical energy to drive a thermodynamically unfavorable redox reaction?

Electrochemical cell

What type of cell involves a thermodynamically favorable reaction?

Galvanic(or voltaic) cells

What type of cell involves a thermodynamically unfavorable reaction?

Electrolytic cell

In both galvanic and electrolytic cells, oxidation(loss of electrons) occurs in the _________ and reduction(gain of electrons) occurs in the _________?

anode/ cathode

What is the flow of electrons in a galvanic cell?

Electrons flow from the anode through the wire to the cathode

In a galvanic cell, both the cathode and anode sit in their own what?

Chambers with ionic solution

What does the ionic solution allow for with the cathode and anode?

The movement of charged particles

In a galvanic cell, if the anode is a metal reactant, its mass ____________ a the metal is converted into ions.

Decreases

In a galvanic cell, if the cathode is a solid that is deposited onto the cathode then the mass of the cathode will ______________.

increase

What is a device which allows for the movement of ions between half-cells?

A salt bridge

The salt bridge contains what?

An inert ionic solution

In a galvanic cell, cations from the salt bridge move towards the CAThode and anions from the salt bridge move towards the ANode. This allows for what?

To allow charge balance to be maintained and it is necessary for a current to flow in the circuit.

What happens if there is not salt bridge in a galvanic cell?

No reaction occurs and no voltage is produced

What type of cell is described:

- Thermodynamically favorable

- anode and cathode in separate chambers

- salt bridge needed

- produces electrical energy

Galvanic cell

What type of cell is described:

- Thermodynamically unfavorable

- anode and cathode are in the same chamber

- no salt bridge is needed

- power source needed

- uses electrical energy

Electrolytic cell

Both galvanic cells and electrolytic cells have what 2 things in common?

1) anode is oxidized; the cathode is reduced

2) require ion flow in the cell for a reaction to occur

For unit 9.7 be able to describe the differences between galvanic and electrolytic cells. Also, be able to identify the anode and cathode based on ion flow from the salt bridge. Be able to describe the electron flow via a provided diagram. Lastly, be able to determine what happens to the mass of the anode and the cathode(anode decrease due to oxidation and cathode increase due to reduction).

For unit 9.7 be able to describe the differences between galvanic and electrolytic cells. Also, be able to identify the anode and cathode based on ion flow from the salt bridge. Be able to describe the electron flow via a provided diagram. Lastly, be able to determine what happens to the mass of the anode and the cathode(anode decrease due to oxidation and cathode increase due to reduction).

Unit 9.8 - Cell Potential and Free Energy

Unit 9.8 - Cell Potential and Free Energy

A reaction occurring in the electrochemical cell involves an electric potential difference(voltage) between what?

The oxidation and reduction processes occurring in the half-cells.

What is the symbol and what are the units for reduction potential?

E; Volts(V)

For an oxidation process(the anode), the reduction half-reaction equation and the sign of the voltage are both what?

Reversed

The equation to find the standard cell potential is what?

ΔE°cell = E°cathode - E°anode

You do not need to flip the sign of the anode when the equation before as the (-) sign in the equation accounts for the negative voltage.

You do not need to flip the sign of the anode when the equation before as the (-) sign in the equation accounts for the negative voltage.

You DO NOT multiply the cell potential when balancing the equation

You DO NOT multiply the cell potential when balancing the equation

Thermodynamically favorable reactions have positive overall cell potentials, therefore, all ____________ cells have positive cell potentials.

galvanic(voltaic)

Thermodynamically unfavorable reactions have negative overall cell potentials, therefore, all __________ cells have negative cell potentials.

electrolytic

Since a reactions favorability factors into the sign of the cell potential(positive = favorable = -ΔG° and vice versa) what equation can be used to relate cell potential and Gibbs free energy?

Faraday's equation: ΔG° = -nFE°cell

Unit 9.9 - Cell Potential Under Nonstandard Conditions

Unit 9.9 - Cell Potential Under Nonstandard Conditions

For unit 9.7 know how to calculate cell potentials and how they correlate with galvanic and electrolytic cells. Also, know how to write the net balanced equation between the anode and the cathode. Lastly, be able to use Faraday's equation to relate Gibbs free energy and cell potential(positive cell potential = favorable = -ΔG° = k>1)

For unit 9.7 know how to calculate cell potentials and how they correlate with galvanic and electrolytic cells. Also, know how to write the net balanced equation between the anode and the cathode. Lastly, be able to use Faraday's equation to relate Gibbs free energy and cell potential(positive cell potential = favorable = -ΔG° = k>1)

Under nonstandard conditions, cell potential (Ecell) depends on the _____________ of reactants and products.

concentrations

At standard cell potential Q = 1, but when a cell operates what happens to the reactants and products?

Reactants are consumed and products are formed and as a result cell potential changes

Changing the mass of solids does not affect the cell potential, because it does not affect Q

Changing the mass of solids does not affect the cell potential, because it does not affect Q

When Q is greater than 1, then the cell potential is __________________ than the standard cell potential.

less

When Q is less than 1, then the cell potential is ______________________ than the standard cell potential.

greater

For unit 9.9 know how to determine what effect different concentrations have of Q and on the cell potential(Q>1 then Ecell

For unit 9.9 know how to determine what effect different concentrations have of Q and on the cell potential(Q>1 then Ecell

Unit 9.10 - Electrolysis and Farday's Law

Unit 9.10 - Electrolysis and Farday's Law

The amount of charge(q) that flows in an electrolytic cell is a function of the current(l) and the time that cell operates(t) which can be summed up in what equation?

l = -q/t

Pay attention to units!

1) Current(A) = C/s

2) Time = s

3) Faraday's constant = 96485c/mol of e-

4) n = moles of e-

For unit 9.10 know how to use dimensional analysis to find different items such as the current, time, of mole of e-.

For unit 9.10 know how to use dimensional analysis to find different items such as the current, time, of mole of e-.

REVIEW NOTES AND DAILY PROBLEM SETS!!!!

REVIEW NOTES AND DAILY PROBLEM SETS!!!!