Unit 7 Flashcards
how do natural processes occur spontaneously
the natural tendencies of processes wanting to go from high energy to low energy and order to disorder
2nd Law of thermodynamics
ALL processes, the entropy of the universe increases. That is, the energy of the universe tends to spread out.
what does the second law of thermodynamics allow you to predict about a reaction
whether or not a chem rxn is spontaneous
0 law of thermodynamics
if two things are the same temp as thirs, they’re also the same temp
1 law of thermodynamics
energy is conserves
deltaE of the universe is equal to 0
3 law of thermo dynamics
a perfect crystal at absolute zero has 0 entropy
what is entropy
Entropy (S) is the dispersion of energy or the extent to which energy is spread out. Entropy is a state function.
whats the best way to think about entropy for most chem rxns
For most chemical systems, the best way to think about entropy is atomic freedom.
how do you calc entropy
Srxn° = nS°,products – mS°,reactants
the boxes are the delta sign
whats gibbs free energy
To simplify various calculations and comparisons, and to make full use of the 2nd Law of Thermodynamics, chemists define another term, Gibbs Free Energy:
G = H – TS
Where H = enthalpy, T = temperature, and S = entropy. G is a state function because H, T, and S are state functions.
equation for gibbs free energy
G = H – TS
Where H = enthalpy, T = temperature, and S = entropy. G is a state function because H, T, and S are state functions.
what does deltaG represent
Unlike ΔSuniverse, ΔG is a measure of energy. Specifically, it tells us about how much work a spontaneous reaction can do, or how much work is needed to make a non-spontaneous reaction go.
ΔG = wmax
collision theory
In order for a chemical reaction to take place, the reactants need to collide
with enough energy.
what 4 things does the kinetics of a reaction depend on
) Temperature
2) Concentration
3) Surface area (for solids)
4) Catalysts / inhibitors
describe temp in the speed of a rxn
Temperature: The hotter a reaction is, the more reactants have enough energy to react. (Hotter = faster reaction)
describe concentration in the speed of a rxn
The more concentrated a solution is, the more often reactants collide. (More concentrated = faster reaction)
describe the surface area for solids in the speed of a reaction
(for solids): Finer powders allow more reactants to collide. (More surface area = faster reaction)
describe the catalysts and inhibitors in the speed of the reaction
Catalysts can speed a reaction by aligning reactants or by changing the reaction mechanism.
whats a rate law
The rate law of a given reaction is a concise mathematical formula that describes the instantaneous rate of that reaction under various conditions.
The rate law of a reaction can only be determined experimentally!
q
general form of a rate law is..
Rate = k [A]x [B]y [C]z
k is the rate constant
(depends on temperature and state of reagents)
A, B, and C are reactants, (catalysts, or inhibitors)
x, y, and z describe how the rate depends on the concentration of A, B, and C
dynamic equilibrium
Movement in two directions occurs at an equal rate so that the system appears to not change
equilibrium
Equilibrium is the state at which forward and reverse rxns occur at the same rate, so the concentration of all species remains constant.
what happens when
Equilibrium is the state at which forward and reverse rxns occur at the same rate, so the concentration of all species remains constant.
what happens with reactions after a certain amount of time
Given enough time, all reactions will eventually reach equilibrium. However, many reactions never reach equilibrium (e.g. rusting metal, living systems, etc.).
what can the equilibrium expression be generalized to?
The equilibrium expression can be generalized to ANY reaction regardless of the rate law! This is extremely important, since it allows us to predict reactant or product concentrations at equilibrium.
equilibrium expression equation
Keq =
[C]y [D]z
[A]w [B]x
