chem II exam 4 study guide

entropy

a measure of the randomness/disorder/messiness

entropy equation

S = k ln W

• k is the Boltzmann constant (1.38 x 10^-23 J/K)

• W is the number of microstates possible

1st law of thermodynamics

energy is conserved

• ΔE_univ = 0

2nd law of thermodynamics

in any spontaneous process, the entropy change in the universe is positive

• ΔS_univ > 0

3rd law of thermodynamics

there is no messiness at absolute zero temperature

• S = 0 when T = 0K

increasing entropy

1. increase temperature

2. increase the number of particles (g)

3. changing phase solid → liquid → gas

• when S ↑ - ΔS +ve

• when S ↓ - ΔS -ve

Gibbs free energy (G)

the sign of ΔG indicates if a reaction will be spontaneous or not

• if ΔG > 0 - the reaction is spontaneous in the forward direction

• if ΔG < 0 - the reaction is nonspontaneous in the forward direction

• if ΔG = 0 - the system is at equilibrium

spontaneous process

• can either be fast or slow

• will occur eventually

• ΔH can either be exothermic or endothermic

• exothermic reactions are generally preferred over endothermic reactions, but it is not always true

  • melting ice is an endothermic process but occurs spontaneously

nonspontaneous process

will not occur eventually

path functions

• depends in the path you take

• there are only 2 path functions

  • work (w)

  • heat (q)

state function

• state functions does not depend on the path

• state functions depends only on the initial and final state ΔV = V_final - V_initial

• all other functions are state functions

  • pressure (P)

  • volume (V)

  • temperature (T)

  • energy (E)

  • enthalpy (H)

  • entropy (S)

entropy changes in chemical reactions

standard free energy of formation

defined as the free energy change for the formation of one mole of a substance from its elements in their standard state at 1 bar and 25C

oxidation-reduction (redox) reactions

where an electron transfer occurs

oxidation numbers

the use of oxidation numbers (or oxidation state) is to describe the transfer of electron (keep track of electron flow)

reducing agent

oxidized - loose electrons

oxidizing agent

reduced - gain electrons

electrochemistry

study of relationships between electricity and chemical reactions

voltaic cells

an electrochemical cell that uses spontaneous redox reactions to generate electricity

• it does not require electricity to drive the reactions

• can be spontaneous

electrolysis/galvanic cell

an electrochemical cell that drives a nonspontaneous redox reaction

• it requires electricity to drive the reaction

• can be nonspontaneous

cell potentials

electrons flow spontaneously from the anode (oxidation) to the cathode (reduction) due to the difference in potential energy

• electrons flow: anode - cathode

anode

• oxidation (OIL)

  • remember the vowels go together

cathode

reduction (RIG)

concentration vs. cell voltage

• during operation of a cell, the concentrations of reactants decrease and products increase

• at some point the voltage nears zero, and the cell is depleted

nernst equation

• determines cell potential at nonstandard states (concentrations)

  • E = E^o - RT/nF lnQ