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What is the rate of disappearance
Used if considering reactant concentration, rxn rate will be based on a decreace in conc. per unit time
What is the rate of appearance
Used if considering reactant concentration, rxn rate will be based on an increase in conc. per unit time
What is the formula for rate of appereance (A→B)
Δ[B]/Δt
What is the formula for rate of disappereance (A→B)
Δ[A]/Δt
What is the instantaneous rate
The rxn rate at one point in time
What are the four ways to monitor rates
Mass, volume, or pressure
Useful when a rxn produces a gas
Change in pH
Used to monitor rxns that produce of consume H+ OH- slowly over time
Change in conductivity
Used for rxns where the total # of ions increases/decreases over time
Change in colour
Useful when a rxn involves aq’s transition metal bc their ions are often colourful
What is the rate law expression
rate = k[A]^M [B]^n
How does the magnitude of k indicate the speed of the rxn
small k = slow rxn
large k = fast rxn
How can the magnitude of k increase
It increases w temperature
What would happen if the reactant is zero
A zero-order reactant
Changing the conc doesn’t affect the rxn rate
Doesn’t participate in the rate-determining step of the rxn
What would happen if the reactant is one
First-order rxn
rate of rxn increases in a linear proportionality to the increase in reactant conc
If [ ] doubles, rate doubles
What would happen if the reactant is two
Second-order reactant
Rate of rxn is exponentially related to rxn conc
If [ ] doubles, rate quadruples
What two things does integrated rate law connect
concentration and time
What is the integrated rate law for first-order reactants
ln [A](t) = -kt + ln[A](o)
What is the integrated rate law for second-order reactants
1/[A](t) = kt + 1/[A](o)
What is the half-life equation for first order reactants
t(1/2) = -ln(1/2) / k
What is the half-life equation for second order reactants
t(1/2) = 1 / k[A](o)
What does the collision theory state
That particles must collide to react
What are the 2 criteria needed for a collision to be successful
Favourable orientation of the colliding particles
Reactant bonds must break and the correct product bonds must form
The appropriate atom must come into contact so their electron densities can interact
Collisions must be energetic enough to surpass the activation energy barrier
What is activation energy
The minimum amount of energy that must be invested to form the activated complex/initiate a rxn
What is the transition state theory
Used to explain what happens as reactants ‘‘transition’’ into products, and can be illustrated using a potential energy diagram
What happens at a transition state
An activated complex forms
How do you find Ea (rev)
Ea (rev) = Ea (fwd) + l ΔH l
What is an activated complex
A temporary particle that forms as a result of a successful collision
What is each small step in a reaction pathway called
Elementary reaction
Each step can’t be further simplified
What is important ab the stoichiometric coefficients in an elementary rxn
Each coefficient is equivalent to the rate law exponents
What is molecularity
How many particles are involved as reactants
What is it called when there is one, two, or three reacting particles
One:
Unimolecular
Two:
Bimolecular
Three:
Termolecular
Why are termolecular rxns unlikely
It is unlikely that 3 reacting particles will collide in correct orientation and energy
What 2 criteria must be met for a mechanism to be plausible
The steps in the mechanism must sum to give the balanced eq’n for the overall rxn
The rate law expression predicted by the rate-determining step in the mechanism needs to be the same as the experimentally determined rate law
When particles are formed in an early step and consumed in a later step
Intermediates
What is a catalyst
A substance that increases the rate of a rxn w/o itself being consumed
What are the two ways catalysts can work
They can hold the reactant particles in correct formation to let proper product bonds form
They can participate in the rxn and alter the rxn mechanism, resulting in a new rxn pathway w a lower activation energy
What’s the difference between a homogeneous and heterogeneous catalyst
A homogeneous catalyst is in the same state/phase as the reactant, while a heterogeneous catalyst is in a diff state/phase as the reactants
When particles are consumed in an early step and formed in a later step
Catalyst
