AP Chemistry Unit 9

The (blank) of a system is a measure of the randomness or dispersion of the system

Entropy or S

The greater the (blank), the greats its entropy

dispersion of a system

Zero entropy is defined as a (blank) at (blank)

• Solid Crystal

• 0 K

All substances that we encounter will have some (blank) value for entropy

positive

The standard entropy change is (blank)

ΔS

The difference between the standard Entropies of products and reactants

S_products - S_reactants

How to predict the sign of ΔS

• Solids are less dispersed than liquids

• if some of the matter is gas you should assume its positive

• if a solid is the only product, there is a negative value

• an aqueous solution is more dispersed than an organized precipitate

• If there are more ions in the reactants, then it will be negative

Gibbs free energy determines (blank)

whether that process is thermodynamically favored or unfavored

Favored or unfavored could also mean (blank)

• spontaneous

• nonspantaneously

How to find ΔG equation

G_products - G_reactants

If G is negative the reaction is (blank)

thermodynamically favored

If G is positive the reaction is (blank)

thermodynamically unfavored

If G is 0 the reaction is (blank)

At equilibrium

Thermodynamically favored processes must result in (blank) or (blank) or (blank)

• decreasing enthalpy

• increasing entropy

• both

Equation that relations favorability, enthalpy and entropy

ΔG = ΔH - TΔS

Negative ΔH, Positive ΔS, Low and High T, and negative ΔG result in (blank)

always favored

Positive ΔH, Positive ΔS, Low and High T, and positive ΔG result in (blank)

Never favored

Positive ΔH, Positive ΔS, Low and High T, and positive ΔG result in (blank)

• Not favored at low temps

• favored at high temps

negative ΔH, negative ΔS, Low and High T, and negative ΔG result in (blank)

• favored at low temps

• not favored at high temps

A substance at a normal phase transition temperature is equally (blank) in either of those two phases. As a result (blank) at that temperature

• stable

• ΔG = 0

Standard Free Energy Change and the Equilibrium Constant equation

ΔG = -RT

Every half reaction has a (blank) associated with it

voltage

Potential Constant

E

The larger the potential for a half-reaction, the more (blank)

likely it is to occur

Two things to consider when calculating the potential of a redox reaction

1. Add the potential for the oxidation to the potential for the reduction

2. never multiply the potential for a half reaction a coefficiet

Galvanic cell is a (blank)

favored redox reaction that is used to generate a flow of current

Current is defined at the (blank)

as the flow of electrons from one place to another

Oxidation takes place at the electrode called the (blank)

Anode

Reduction takes place at the (blank)

Cathode

At the cathode, the solution becomes (blank) and the (blank) from the salt bridge solution flow into the half cell

• less positively charged

• positive cations

At the anode, where oxidation occurs the solution is becoming more (blank) and the (blank) from the salt bridge solution flow into the half-cell

• more positively charger

• negative anions

Under standard conditions, the voltage of the cell is the (blank) as the total voltage of the (blank)

• same

• redox reaction

Standard conditions for voltaic cells is (blank)

25 C, 1.0 atm and a concentration of 1.0 M

• Any deviation will result in the cell potential also deviating

Voltaic cells are are very (blank) having equilibrium constants greater than (blank)

• favored

• 1

If Q for a voltaic cell becomes equal to the equilibrium constant, the voltage becomes (blank)

zero

To determine if a cell’s potential will change if the standard condition is deviated to use (blank)

The reaction Quotient

The reaction quotient will equal to 1 unless (blank) which would cause the Q to become closer to the equilibrium constant therefore making it (blank)

• increase in concentration of a product, or decrease in reacts

• decrease

(blank) can also affect the Q and a change in (blank)

• Pressue

• Temperature

An outside source of voltage is used to (blank) redox reactions to take place

force an unfavored

the anode and cathode are usually just (blank)

metal bars that conduct currents

The sign of you total cell potential (E) should always be (blank)

negative

When a current will run through a molten compound or pure water, you do not have determine redox reactions because (blank)

There will only be one choice for each

Electrolytic cells are used for (blank)

electroplating

Four steps to figure out electrolysis probelms

1. Calculate the charge in coulombs

2. you now know the amount of electrons

3. when you find the moles of electrons you know the half-reaction

4. once you know the moles of metal, you can calculate the number of grams

A redox reaction will be favored if (blank)

its potential has a postive valuei

A reaction that is favored has a (blank) for (blank)

• negative value

• free energy change

Equation for reaction potential and free energy for a redox reaction

ΔG = -nFE

If E is positive, G is (blank) and the reaction is (blank)

• negative

• favored

If E is negative, G is (blank) and the reaction is (blank)

• positive

• unfavored