(sum of S products) - (sum of S reactants)
DO NOT FORGET TO ACCOUNT FOR THE MOLES IN THE REACTION!!!
cathode
as temperature goes to zero, entropy approaches a constant value
galvanic cell vs electrolytic cell
galvanic = anode is negative and cathode is positive
electrolytic = anode is positive and cathode is negative
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 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
2nd law with entropy
S = entropy
G = Gibbs free energy
H = heat energy
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
non-spontaneous is...
thermodynamically unfavorable
a reaction can be coupled with a reaction that is favorable to push it forward
Examples:
- photosynthesis
- ATP
- Charging a battery with electricity
is H > 0 and S > 0
T = 500k
spontaneous, high temperature, T delta S is large
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
is H < 0 and S < 0
T=100k
spontaneous, low temperature, T delta S is small
charging a battery vs using a battery
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
exergonic reaction
products have less energy than reactants, spontaneous, graph will end lower than it started
if a reaction is kinetically favorable
it has k>1, relatively low activation energy
voltage equation
oxidation happens, losing electrons
volumes proportionality with entropy
as V goes up, so does S
as the more temperature, the more energy, the mor entropy
2nd law of thermodynamics
entropy
degrees of freedom of a molecule
overall cell reaction
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.
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!!
cell potential, Ecell, electromotive force (emf)
1 joule of work / coulomb of charge transferred
J/C = units
spontaneous at all Temps, delta G <0
oxidation half-reaction
x --> X+ + e-
