Reaction Rates Flashcards
Reaction rates
- measured in terms of the rate of disappearance of a reactant or appearance of a product
- rates are expressed by moles per liter (mol/L) or molarity per second (M/s)
Rate Laws
take form of
rate = k[A]^x[B]^y
x and y = the order of reaction
overall order of the reaction = x + y
must be determined from experimental data
Rate order of a reaction is
the sum of all individual rate orders in the rate law
Zero - order reactions
- have constant rate that does not depend on the concentration of reactants
- only factors affecting the are of zero - order reaction:
temperature & addition of a catalyst - concentration VS time curve of a zero - order reaction rate is a straight line; the slope of such a line is equal to -k
- Rate of formation of product C is independent of changes in concentrations of any of the reactants, A and B.
rate = k[A]^0[B]^0 = k
units: M/s
First - order reactions
- have a non-constant rate that depends on the concentration of reactant
- concentration VS time curve of a first - order reaction rate is a non linear
- directly proportional to one reactant, such that doubling the concenratio of that rectant results in a doubling of the rate of formation of the product
- the slope of a ln[A] VS time plot is -k
- graph shows that the rate of formation of product is dependent on the concentration of reactant
rate = k[A]^1 or rate = k[B]^1
units: M/s
Second - order reactions
- rate is proportional to either the concentrations of two reactants or to the square of the concentration of a single reactant.
- have a non-constant rate that depends on the concentration of reactant
- concentration VS time curve of a second - order reaction rate is a non linear
- the slope of a 1/[A] VS time plot is k
- graph curve shows that the rate of formation of product is dependent on the concentration of reactant
rate = k[A]^1[B]^1 or rate = k[A]^2 or rate = k[B]^2
units: M/s
Broken order reactions
those with non-integer (fractions) orders
Mixed order reactions
those that have a rate order that changes over time
Zero order:
temperature is decreased so, the rate is
decreased
First order:
temperature is decreased so, the rate is
decreased
Second order:
temperature is decreased so, the rate is
decreased
Zero order:
all reactants’ concentrations doubled so, the rate is
unaffected
First order:
all reactants’ concentrations doubled so, the rate is
doubled
Second order:
all reactants’ concentrations doubled so, the rate is
multiplied by 4
Zero order:
catalyst is added so, the rate is
increased
