overall cell reaction
y + z --> Y+ + Z- (G<0)
charging a battery vs using a battery
3rd law of thermodynamics
what is Gibb's free energy
the energy of a system related to changes in enthalpy and entropy, at a constant temperature.
basically implies that the system is at 1 atm and using 1 M solutions.
exergonic reaction
products have less energy than reactants, spontaneous, graph will end lower than it started
cell potential, Ecell, electromotive force (emf)
1 joule of work / coulomb of charge transferred
J/C = units
is H < 0 and S < 0
volumes proportionality with entropy
galvanic = anode is negative and cathode is positive
electrolytic = anode is positive and cathode is negative
S = entropy
G = Gibbs free energy
H = heat 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!!
it has k>1, relatively low activation energy
cathode
delta G and the energy of the product is lower than that of the reactants
1. G = negative = k>1; G = positive = k
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
delta G = delta H - (T * delta S)
gibbs free energy = enthalpy - (temperature times entropy)
*note T is in kelvin, not Celsius
is H > 0 and S > 0
T = 500k
spontaneous, high temperature, T delta S is large
delta S =
(sum of S products) - (sum of S reactants)
DO NOT FORGET TO ACCOUNT FOR THE MOLES IN THE REACTION!!!
voltage equation
V = IR
voltage = current (amps) * resistance (ohms)
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
is H < 0 and S > 0
spontaneous at all Temps, delta G <0
oxidation happens, losing electrons
non-spontaneous is...
thermodynamically unfavorable
how K and G relate to each other
oxidation half-reaction
x --> X+ + e-
entropy of an isolated system is never decreasing, only if it is in a 2 or more system
galvanic cell
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
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
degrees of freedom of a molecule
