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
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
how do you calculate Gibbs free energy
delta G = delta H - (T * delta S)
gibbs free energy = enthalpy - (temperature times entropy)
*note T is in kelvin, not Celsius
volumes proportionality with entropy
as V goes up, so does S
as the more temperature, the more energy, the mor entropy
is H < 0 and S < 0
T=100k
spontaneous, low temperature, T delta S is small
G, S, H
S = entropy
G = Gibbs free energy
H = heat energy
oxidation half-reaction
x --> X+ + e-
products have less energy than reactants, spontaneous, graph will end lower than it started
oxidation happens, losing electrons
voltage equation
V = IR
voltage = current (amps) * resistance (ohms)
entropy
degrees of freedom of a molecule
cathode
reduction happens, gaining electrons
is H < 0 and S > 0
spontaneous at all Temps, delta G <0
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
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.
(sum of S products) - (sum of S reactants)
DO NOT FORGET TO ACCOUNT FOR THE MOLES IN THE REACTION!!!
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!!
galvanic cell vs electrolytic cell
galvanic = anode is negative and cathode is positive
electrolytic = anode is positive and cathode is negative
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
a reaction can be coupled with a reaction that is favorable to push it forward
Examples:
- photosynthesis
- ATP
- Charging a battery with electricity
thermodynamically unfavorable
cell potential, Ecell, electromotive force (emf)
1 joule of work / coulomb of charge transferred
J/C = units
2nd law of thermodynamics
entropy of an isolated system is never decreasing, only if it is in a 2 or more system
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
overall cell reaction
y + z --> Y+ + Z- (G<0)
is H > 0 and S > 0
T = 500k
spontaneous, high temperature, T delta S is large
3rd law of thermodynamics
charging a battery vs using a battery
if a reaction is kinetically favorable
