2nd law of thermodynamics
entropy of an isolated system is never decreasing, only if it is in a 2 or more system
entropy
if a reaction is kinetically favorable
it has k>1, relatively low activation energy
as temperature goes to zero, entropy approaches a constant value
what is Gibb's free energy
Cell potential equation
Ecell = E (cathode) - E (anode)
IMPORTANT: if the reaction gets reversed (in order to balance, sometimes it will need to be reversed), the sign of the Ecell must switch, however if it gets multiplied (in order to balance) IT REMAINS THE SAME!!
delta S =
(sum of S products) - (sum of S reactants)
DO NOT FORGET TO ACCOUNT FOR THE MOLES IN THE REACTION!!!
G = negative = k>1
G = positive = k<1
k is close to 1, G is close to zero
k is far from 1, G is far from zero
delta G = delta H - (T * delta S)
gibbs free energy = enthalpy - (temperature times entropy)
*note T is in kelvin, not Celsius
x --> X+ + e-
voltage equation
V = IR
voltage = current (amps) * resistance (ohms)
products have less energy than reactants, spontaneous, graph will end lower than it started
chemical energy is converted to electrical energy with spontaneous redox reaction
Voltage
consists of oxidizing agent in one compartment that pulls electrons through a wire from a reducing agent
1st law of thermodynamics
in an isolated system energy can neither be created or destroyed; only transferred or converted, meaning E lost = negative E gained
overall cell reaction
y + z --> Y+ + Z- (G<0)
charging a battery vs using a battery
charging = non-spontaneous
using = spontaneous
S = entropy
G = Gibbs free energy
H = heat energy
spontaneous at all Temps, delta G <0
1 joule of work / coulomb of charge transferred
J/C = units
volumes proportionality with entropy
as V goes up, so does S
as the more temperature, the more energy, the mor entropy
galvanic = anode is negative and cathode is positive
electrolytic = anode is positive and cathode is negative
T = 500k
spontaneous, high temperature, T delta S is large
is H < 0 and S < 0
T=100k
spontaneous, low temperature, T delta S is small
if a reaction is thermodynamically favorable
delta G and the energy of the product is lower than that of the reactants
1. G = negative = k>1; G = positive = k
how a reaction that is thermodynamically unfavorable occur
a reaction can be coupled with a reaction that is favorable to push it forward
Examples:
- photosynthesis
- ATP
- Charging a battery with electricity
anode
oxidation happens, losing electrons
non-spontaneous is...
thermodynamically unfavorable
cathode
reduction happens, gaining electrons
2nd law with entropy
as matter disperses, entropy increase, so, going from solid to liquid to gas would increase entropy, whilst going from gas to liquid to solid would decrease it
