Studied by 166 peopleRate of reaction
change in amount of a reactant or product per unit time
Rate expression
Math representation of rate of reaction
Rate of a reaction is equal to
rate of change of a reactant/product divided by its coefficient
Are products positive or negative in rates of expression?
positive
Are reactants positive or negative in rates of expression?
negative
Average reaction rate
rate at which reactions proceeds over a period of time
Initial reaction rate
rate at which a reaction is proceeding at a specific time
Instantaneous Reaction Rate
the rate at which a reaction is proceeding at a specific time
As you move down a group, the alkali metals react at a faster or slower rate with water?
faster
What number tells the order of a rate law?
The exponent
Are reactants the only thing in a rate law?
yes
m is order with respect to
A
n is oder with respect to
B
What do you add to find the overall order?
m and n
First order reaction equation
rate=k[a]
Integration with respect to time first order equation
ln [A]0/[a]t = kt
First order reaction equation in slope equation form
ln[a]= -kt + ln[a]0
Zero order has a positive or negative slope?
negative
First order has a positive or negative slope?
negative
Second order has a positive or negative slope?
positive
Zero order plot of concentration vs time
[A] vs time
First order plot of concentration vs time
ln[A]
Second order plot of concentration vs time
1/[A]
Integrated rate law for zero order
[A]t= -kt + [A]0
Integrated rate law for second order
1/[A]t= kt + 1/[A]0
Half-life definition
time it takes for half of the reacant amount to be consumed
Half-life equation
[A]t = ½ [A]0
Half-life equation for first order
t1/2= 0.693/k
Units for 0 order reaction
m/s
Units for first order reaction
s^-1
Units for second order reaction
m^-1/s^-1
Collision Theory
Reactants must collide in order to react with each other
Rate of reaction is proportional to
rate of reactant collisions
Increasing the temp often leads to an increase or decrease in rate of reaction?
increase
Temperature increases the average what of reactants?
Kinetic energy
Arrhenius Equation
k= Ae^ -Ea/RT
The lower the Ea, the faster or slower the reaction?
Faster
Catalyst only effects
activation energy
Catalyst definition
Substance that can increase the reaction rate without being used up in the reaction
Intermediates definition
Species that are produced in one step and consumed in a subsequent step
Why is activation energy changed by adding a catalyst?
The catalyst changes the reaction mechanism
At equilibrium, the amount of reactants and products
stops changing
Equilibrium equation
k= products/reactants
Are solids and liquids included in equilibrium expressions?
no
The reaction will reach equilibrium when most of the reactant turns into a product
large k
The reaction will reach equilibrium after very little reactant has been converted to product
small k
If Qc=Kc
reaction is at equilibrium
If Qc is less than Kc
the reaction proceeds in the forward direction
If Qc is greater than Kc
the reaction proceeds in the reverse direction
Le Chatelier’s principle
When a chemical system at equilibrium is disturbed, it returns to equilibrium by counteracting the disturbance
Do liquids and solids have an effect on Le Chatelier’s principle
no
Four factors that affect rate of a reaction
concentration, temperature, surface area of a solid reactant, and catalysts
If heat is a product
k decreases
If heat is a reactant
k increases
The reaction rate of a 60 degree reaction will be greater than at 30 degrees because
there is a greater proportion of reactants with the necessary kinetic energy to react
What could decrease the rate of a reaction?
decreasing the surface area
At equilibrium what is equal to the rate of the reverse reaction?
the rate of the forward reaction
Does the magnitude of k indicate how rapidly or slowly equilibrium will be reached?
no
What is the order of the reaction when a graph of ln[a] vs. time gives a straight line with a negative slope?
first
What order of reaction has a linear curve when plotting concentration vs time
zero
What is the effect on k as the activation energy for a reaction increases?
it decreases
An increase in the temperature would result in an increase in the value of the
rate constant
The molecularity of an elementary step is determined by
how many reactants are involved in the reaction
To determine the rate law for a mechanism containing the equilibrium step, you must redefine
the intermediate in terms of the equilibrium step
Can you have any intermediates in the rate law?
no
Catalysts increase reaction rates by
providing an alternate reaction mechanism with a lower activation energy
Another way to describe a species that slows down the reaction rate is
as an inhibitor
Note
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