Lecture 4 Flashcards
The collision theory
For a reaction to occur molecules must collide.
Assumes the rate of the reaction is proportional to the number of molecular collisions per second
What do molecules need to have an effective collision?
1) Molecules must have proper orientation towards each other
2) Molecules must have enough energy to break bonds (Activation energy)
Activation energy?
Minimum amount of energy to initiate a chemical reaction.
Low temperature has _____ rate
slow
Less energy fewer collisions
High temperature has ____ rate
fast
More energy more frequent collisions
Rate of Reaction equation
aA + bB –> cC + dD
Rate of reaction = -1/a(A/t) = - 1/b(B/t)
.. ect for rest of equation
Why do reaction slow over time?
Depletion of reactants, temperature changes, loss of catalyst, decrease in number of collisions
Rate law expression
Rate = K[A]x[B]y
The larger the K value…
The faster the reaction
Reaction Order??
Radioactive decay
Large range of half-lives
Photodissociation
Absorption of photon
Pseudo first order
A reaction that should be 2nd order but the B reactant is in higher concentration than A so its first order
Unimolecular
a single molecule dissociates
Biomolecular
the collision of 2 molecules
Termolecular
simultaneous collision of 3 molecules
Residence time
fancyT = m/f
M = amount of chemical
F = influx or efflux of chemical
Renewal time
The time required to completely displace original chemicals from reservoir.
Water entering the bottom of the tank steadily replaces the water lying above it without mixing
Renewal time with no mixing
Residence time is equal to renewal time
fancy T = T
Renewal time with perfect mixing
rate of removal of dirty water is proportional to amount of dirty water in tank
dw/dt = -KW
facy T = 1/K
Dynamic equilibrium
What rate of forward and reverse are equal
Equilibrium constant
K = Products/reactants
Chemical activity
a=C/Cstandrad state
its untless
Standard states
solutes –> 1M, 1 bar, 298K
Liquids & Solids –> 1 par, 298K
Gases –> 1bar, 298K
Reaction Quotient compared to K values
Q > K system shifts left
Q = K equilibrium
Q < K system shifts right
Endothermic
absorbs energy, loses heat
Exothermic
releases energy, heat is produced
A Catalyst has ____ effect on conditions of equilibrium it only affects _____
NO
the rate of reaction
