Exam 2 Flashcards
Delta S (universe) > 0; Delta G < 0
Process is spontaneous as written
Delta S (universe) = 0; Delta G = 0
Reversible (process is not spontaneous in either direction) - system is at equilibrium
Delta S (universe) < 0; Delta G > 0
Process is spontaneous in reverse direction
Delta H = (-); Delta S = (-); -T Delta S = (+)
Spontaneous at low temp
Delta H = (+); Delta S = (+); -T Delta S = (-)
Spontaneous at high temp
What is physically happening to make Delta S»_space;> 0?
Formation of ions, ion-solvent interactions, increased disorder
What is physically happening to make Delta H»_space;> 0?
Absorbing heat in the dissolution process
If Delta G = 0, what equation can you use?
0 = Delta S (system) - T Delta S (system)
Rate of disappearance and rate of appearance
stoichiometric value of reactant / stoichiometric value of product = disappearance of reaction is ____ the appearance of product
Information we can get from kinetics
Speed, factors that influence speed; molecular mechanism (how the reaction occurs)
How do chemicals react?
must collide with enough energy and in the correct orientation
The more homogeneous the mixture of reactants
the faster the molecules can react
As the concentration of reactants increases
the likelihood that reactant molecules will collide increases
Catalyst
speed up reactions by changing the mechanism of the reaction; not consumed during the course of the overall reaction
Rate law
Rate = k[A]^n[B]^m ; n = reaction order of A; m = reaction order of B; overall reaction order = n + m
Determining Rate laws using Initial rates (change the concentration of only one of the reactants)
Rate 2/Rate 1 = k[B2]^n [C2]^m / k[B1]^n [C1]^m
Zero Order Equations
[At] = [Ao] -kt
Zero Order Graph
m = -k; y-intercept = [Ao], concentration as a function of time
1st order Equations
ln [At]/[Ao] = -kt ; [At] = [Ao]e^-kt
2nd order Equations
1/[At] - 1/[Ao] = kt; 1/[At] = kt + 1/[Ao]
Zero Order Equations
0.5[Ao] /k = t1/2
1st order Equations
ln2/k = t1/2
2nd order Equations
1/k[Ao] = t1/2
Transition State
The (rare) arrangement of atoms at the energy maximum during the course of the reaction
Activation Energy
the energy required to overcome the reaction barrier
k = Ae^(-Ea/RT)
A is the frequency factor, Ea is the activation energy, T is the absolute temperature
Intermediates are written
written below the line at each step
Transition states are written
above the line
the number of steps in the mechanism is indicated by
counted based on the bottom of each “hill”
A catalyst influence the rate of a reaction by altering
the value of Ea
A catalyst does not alter
the delta E of a reaction
catalysts are often prepared so they have ________ surface areas
very large
the rate-determining step is
the slowest reaction
unimolecular
only on reactant involved; A —> products
Bimolecular
two molecules must collide to produce products; A + B ——> Products; 2A —–> Products
Termolecular
three different molecules must collide; A + B + C —-> Products; A + 2B —–> Products; 3A ——> Products
Exothermic reaction graph
reactants are higher than the products
Endothermic reaction graph
reactants are lower than the products
Homogenous Catalyst
has the same phase as the molecules in the reaction
Heterogenous Catalyst
has a different phase than the molecules in the reaction
Equilibrium is a state of dynamic molecular behavior, meaning that
reactants turn into products and products turn into reactants at equal rates
Equilibrium can only be achieved in a ______ system
closed system
Kf/Kr = keq
forward and reverse reactions
Equilibirum constant expressions
product/reactants; only gas and aqueous
Kc«< 1
Reactant Favored, reactant predominates at equilibrium
Kc»>1
Product Favored, product predominates at equilibrium
Qc has the same form as Keq
but there is no assumption of equilibrium
Q<K
System has too much reactant; shift toward product
Q=K
System is at equilibrium
Q>K
System has too much product; shift toward reaction
