AP Chem Unit 9

Standard sign (little degree symbol) , can be on the top of Deltha H , S , or G

With the standard sign, these are calculated at 25 C (298K) temp

Entropy, S, of a system is?

The measure of randomness or dispersion of the system; the greater the dispersion of a system, the greater its entropy.

(Zero entropy is defined as a solid crystal at 0 K, and because 0k has never been reached experimentally)

Standard Entropy Change , Delta S, change in dispersion

Delta S= Sum of S of products - Sum of S of reactants

More dispersion Positive

Less dispersion negative

You can predict Delta S sign by phase changes

Solid < liquid < Gas

If the reaction has more molecules (coefficients ) on the product side, when all the states are the same, the?

Delta S is Positive, because More dispersion

If state & molecules are both the same, you can also account for ions, ?

Yes, more ions more dispersion

However you can only count ions/ molecules if you are looking at the ________ phases

Aqueous or gas

Gibbs free energy G

Determines whether process is thermodynamically favored or not,

We always use thermodynamically favored in AP chemistry

Standard Free energy change, DELTA G

Delta G = Sum of G of products - sum of G of reactants

Delta G = negative, thermodynamically favored

Delta G= positive, thermodynamically unfavored

Delta = 0, equilibrium

How to find Delta G, use this equation:

IMPORTANT relates favorability (Delta G, H ,S)

Delta G = Delta H - T * delta S

T = Kelvin

You can always use Delta G= Delta H - T * Delta S

To find if reactions are favored, and at which temp are favored,

But here is graph just in case

U don’t really need to remember this you can just manipulate formula

Delta G and phase change, if we need to find phase transition temperature , what do we do.

Since phase transition temperature is equally stable in either of 2 phase, WE CAN SET DELTA G = 0 at that temperature, If we have data regard thermodynamic properties at the point of fusion or vaporization we can determine boiling point or melting ponit

Standard free energy change and the equilibrium constant (Given)

While this R is same, BE VERY CAREFUL YOU ARE USING CORRECT VALUE FOR R, use 8.31 j/mol

Reduction potential Zn 2+ + 2e- → Zn(s) E= -0.76 V

Every Half reaction has an electric potential, or voltage associated. (Always Given)

You can always read them in reverse and flip the sign on the voltage to get oxidation potentials

The larger the potential for a half reaction, the _____ likely it is going to occur

more

For a galvanic / voltaic cell always has a _____ cell potential.

Postive

Add the two potentials to calculate for the _________________.

Calculate the potential of a redox reaction. (Positive for galvanic, negative for electrolytic)

Rule when manipulating Half-reactions

Never multiply the potential for a half reaction by a coefficient, even you if multiplied on one side.

Galvanic / Voltaic Cell

A favored redox reaction is used t generate a flow of current.

If salt bridge removed, the voltage would drop to zero, because would become electrically imbalanced

Voltage flow keeps on going until anode runs out

Overall E always postive

AN OX, RED CAT , OIL RIG

Mnemonic device to help remember

Anode has oxidation ANOX

Reduction happens in cathode RED CAT

Oil oxidation is loss electron

Rig reduction is gain electron

Current

The flow of electrons from one place to another

In galvanic cell, current flow from _______ to ______.

Anode to cathode

Ion in salt bridge flow _____ to______

_______ to ____

Anion to anode

Cation to cathode

Galvanic cell is like a ______ functioning

A electrolytic cell is like ______ a battery

Battery

Recharging

Electrolytic cell

Is like running a galvanic cell backward,

Overall E is always negative

Outside force is used to force an unfavored redox reaction to take place

Non standard conditions, if concentration would cause cell potential to deviate.

(Q = K), dead battery, The voltage of the cell would drop to zero.

Any change to the cell that would cause the reaction quotient to increase ( such as an increase concentration of a product),

Would cause the reaction quotient to become closer to the equilibrium constant and would thus decrease the cell potential

Ernest equation (NO Calculation required)

You can use it to mathematically justify the change in cell potential under non-standard conditions.

Increasing reactant quotient would cause Q term to increase, which would cause E cell to decrease

Electroplating

Use stoichiometry to calculate electroplating problems,

Electroplating is a process where well use electrical current and see how much metal “plates out”

Current (A) = ?

Amps = Coulombs / time (seconds)

Moles of electron to coulombs

1 mole of e- = 96500

Voltage and favorability equation (given)

Delta G= - n FE

Make sure you can do calculations with this