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
if a reaction is kinetically favorable
it has k>1, relatively low activation energy
a reaction can be coupled with a reaction that is favorable to push it forward
Examples:
- photosynthesis
- ATP
- Charging a battery with electricity
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!!
entropy
oxidation half-reaction
x --> X+ + e-
voltage equation
galvanic cell vs electrolytic cell
galvanic = anode is negative and cathode is positive
electrolytic = anode is positive and cathode is negative
cell potential, Ecell, electromotive force (emf)
as V goes up, so does S
as the more temperature, the more energy, the mor entropy
is H < 0 and S > 0
spontaneous at all Temps, delta G <0
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
non-spontaneous is...
thermodynamically unfavorable
3rd law of thermodynamics
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
S = entropy
G = Gibbs free energy
H = heat energy
anode
(sum of S products) - (sum of S reactants)
DO NOT FORGET TO ACCOUNT FOR THE MOLES IN THE REACTION!!!
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.
charging a battery vs using a battery
charging = non-spontaneous
using = spontaneous
products have less energy than reactants, spontaneous, graph will end lower than it started
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 K and G relate to each other
entropy of an isolated system is never decreasing, only if it is in a 2 or more system
is H < 0 and S < 0
overall cell reaction
y + z --> Y+ + Z- (G<0)
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
