43 terms

Chemical kinetics (unit 3)

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reaction rate
the speed at which a chemical reaction occurs
reaction mechanism
step-by-step molecular level view or the pathway from reactants to products
chemical kinetics
the area or chemistry concerned with the speeds, or rates of reactions
-it relates to how quickly a medicine works in the boyd, towhether the processes that from and deplete ozone in the atmosphere are in balance, and to such industrial challenges as the development of the catalysts
catalysts
materials that speed up reactions
-are agents that increase reaction rates without themselves being used up
4 factors that affect reaction rates
1.physical state of the reactants
2.reactant concentrations
3.reaction temperature
4.the presence of a catalyst
on a molecular level, reaction rates depend on the
frequency of collisions between molecules-the greater the frequency of collisions, the higher the reaction rate
the speed of an event is defined
as the change that occurs in a given time interval, which means that whenever we talk about speed, we necessarily bring in the notion of time.
the speed of a chemical reaction (its reaction time) is the change
in the concentration of reactants or products per unit of time
the average rate of disappearance or B formula
change in concentration of B/ change in time
∆B/∆t
it is typical for rates to decrease as a reaction proceeds because
the concentration of reactants decreases
instantaneous rate
the rate at a particular instant during the reaction
-it is determined from the slope of the cure at a particular point in time
instantanous rate formula
change in molarity/change in time
∆m/∆t
rate
means instantaneous rate
during a trip for example the instantaneous speed at any moment is the speedometer reading at that moment
initial rate
instantaneous rate at t=0
the rate of disappearance A ...... the disappearance of substance B
equals
rate law
an equation that shows how the rate depends on reactant concentrations
rate constant
the magnitude of the rate constant (k) changes with temperature and therefore determines how temp affects rate.
reaction orders
the exponents m and n in the rate lw formula
overall reaction order
is the sum of the orders with respect to each reactant represented in the rate law
the exponents in the rate law indicate
how the rate is affected by each reactant concentration
large value of k (10⁹ or higher) indicates.....
small value of k (10 or lower) indicates....
means a fast reaction
slow reaction
units of rate constant formula
units of rate constant= units of rate / units of concentration ²
(M/s) / M²
first-order reaction rate constant unit
s⁻¹
The rate of a second order reaction can depend on the concentrations of more than one reactant. T/F
TRUE
half life
decrease of 50% in a time period
As the temperature of a reaction is increased, the rate of the reaction increases because the
reactant molecules collide more frequently and with greater energy per collision
The rate of a reaction depends on
collision orientation, collision energy,collision frequency
In general, as temperature goes up, reaction rate
goes up regardless of whether the reaction is exothermic or endothermic
elementary reaction
reactions that occur in a single event or step
molecularity or the reaction is defined
by the number of molecules that participate as reactants in an elementary reactions
The mechanism for formation of the product X is:

A + B → C + D (slow)
B + D → X (fast)

The intermediate reactant in the reaction is __________.
D
The half-life for a first order rate law depends on the starting concentration.
T/F
FALSE
The rate of a second order reaction can depend on the concentrations of more than one reactant. T/F
TRUE
One difference between first- and second-order reactions is that __________.
the half-life of a first-order reaction does not depend on [A]0; the half-life of a second-order reaction does depend on [A]0
In general, as temperature goes down, reaction rate __________.
goes down regardless of whether the reaction is exothermic or endothermic
Elementary reactions involving the simultaneous collision of three molecules are __________.
termolecular
Elementary reactions involving the simultaneous collision of two molecules are __________.
bimolecular
A catalyst can increase the rate of a reaction __________.
by providing an alternative pathway with a lower activation energy
The rate limiting step in a reaction is the slowest step in the reaction sequence. T/F
TRUE
catalyst
is a substance that changes the speed of a chemical reaction without undergoing a permanent chemical change itself.
homogenous catalysts
are catalyst that is present in the same phase (state) as the reactants in a reaction mixture
heterogeneous catalysts
are catalyst that are present in a different state as the reactants in a reaction mixture
Of the following, __________ will lower the activation energy for a reaction.
adding a catalyst for the reaction
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