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unit 9 must knows

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1st law of thermodynamics ☝️ Click to use flashcards

unit 9 must knows

31 Flashcards 0 recently 0/10

Elias A

unit 9: application of thermodynamics

Physical chemistry

Terms

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
2nd law of thermodynamics
 entropy of an isolated system is never decreasing, only if it is in a 2 or more system
3rd law of thermodynamics
 as temperature goes to zero, entropy approaches a constant value
G, S, H
 S = entropy G = Gibbs free energy H = heat energy
entropy
 degrees of freedom of a molecule
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
volumes proportionality with entropy
 as V goes up, so does S as the more temperature, the more energy, the mor entropy
delta S =
 (sum of S products) - (sum of S reactants) DO NOT FORGET TO ACCOUNT FOR THE MOLES IN THE 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.
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
is H > 0 and S > 0
 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
is H < 0 and S > 0
 spontaneous at all Temps, delta G <0
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
if a reaction is kinetically favorable
 it has k>1, relatively low activation energy
how K and G relate to each other
 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 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
exergonic reaction
 products have less energy than reactants, spontaneous, graph will end lower than it started
charging a battery vs using a battery
 charging = non-spontaneous using = spontaneous
voltage equation
 V = IR voltage = current (amps) * resistance (ohms)
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
anode
 oxidation happens, losing electrons
cathode
 reduction happens, gaining electrons
oxidation half-reaction
 x --> X+ + e-
non-spontaneous is...
thermodynamically unfavorable
overall cell reaction
 y + z --> Y+ + Z- (G<0)
cell potential, Ecell, electromotive force (emf)
 1 joule of work / coulomb of charge transferred J/C = units
galvanic cell vs electrolytic cell
 galvanic = anode is negative and cathode is positive electrolytic = anode is positive and cathode is negative
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!!