Chpt 14: Chemical Kinetics Flashcards
what is an integrated rate law?
expressions for reaction rate that integrate concentration AND time
what is a Heterogeneous catalyst?
A rxn catalyst that is in a different phase than the reactants
why can’t stoichiometry be used to determine the rate order of a chemical reaction?
because stoichiometry reflects the overall net reaction being examined, but does not account for any of the elementary reactions required to produce the overall net reaction
does each reactant in a rate law have its own rate order?
yes
4 factors that effect chemical reaction rates
- Physical state of reactants
- concentration
- Temperature
- Presence of catalysts
Surface area of atoms makes a difference, too. Thanks, Khan!
what are the units for a zero order reaction’s rate constant?
M/s
what are the 3 types of molecularity
- Unimolecular
- Bimolecular
- Termolecular
which mathematical description of reaction rates uses reaction stoichiometry?
basic reaction rate
how are integrated rate laws different from ‘regular’ rate laws?
integrated rate laws let you determine/compare specific concentrations at specific times
what does the slope tell you in a zero order graph of [M] vs time?
-k constant
what does the slope tell you in a second order graph of 1/[M] vs time?
k
how are instantaneous reaction rates approximated?
the slope of a point on a graph of delta concentration vs delta time
on a rxn energy profile (where elementary steps are involved), are transition states shown as humps or dips?
humps
energy spikes as activation complex forms, then drops as reaction proceeds
when examining reaction rates, what is a tangent line used for?
A tangent line can be placed along the graph, through a particular point in time (along the x axis), and the tangent line’s slope can be calculated to provide the instantaneous rate for the selected time point
what does a Negative catalyst do?
Slow down rxns
which order of integrated rate law expression involves ln [M] values?
first order
what 2 factors are k constants dependent upon in the Arrhenius eqn?
frequency factor and activation energy
what is ‘chemical Kinetics’ the study of?
study and discussion of how reactions progress, particularly with regard to reaction rates/speeds
what is the equation for a basic reaction rate
delta concentration/delta time
which type of reaction rate expression employs instantaneous and average rates?
basic reaction rates
how are average reaction rates approximated?
with delta concentration/delta time
on a rxn energy profile (where elementary steps are involved), are intermediates shown as humps or dips?
dips
intermediates are formed right after activation complexes [shown as humps] resolve
do products get written into reaction rate expressions?
no.
what range of K constant values indicate that a reaction is relatively fast?
values equal to 10^9 or bigger
in math r/t rates, how can you ‘bring a number down’ from the exponents?
‘take the ln’ of the value in the exponent.
You have to do this to all terms on both sides of the equation
what are the units for a first order reaction’s rate constant?
s-1 or 1/s
when we say ‘initial rate’, what are we actually referring to?
the rate of a reaction at any given point in time (as shown on a graph)…because chemists don’t speak English…😒
which mathematical description of reaction rates uses the concept of ‘reaction order’?
rate law and integrated rate law
which order of integrated rate law expression involves [M] values?
zero order
what is an ‘average reaction rate’ the average of?
reaction’s initial rates, over a specified period of time
what does the slope tell you in a first order graph of ln [M] vs time?
-k
how does Adsortion occur (in the context of catalysts’ participation in chemical reactions)?
reacting molecules bind to the surface of a catalyst, and this lowers the activation energy
which order of integrated rate law expression involves 1/[M] values?
second order
in math r/t rates, how can ‘cancel’ an ‘ln’ in your equation???
raise “e” to the expression with the ln in it???
You have to do this to all terms on both sides of the equation
what is the difference between a reaction ‘transition state’ and a reaction ‘intermediate’?
A reaction ‘intermediate’ is a compound that is created and then immediately consumed as part of a rate mechanism. A reaction ‘transition state’ is what you call two molecules (who have collided and become distorted) right before they react with one another
How is rate order determined in rate laws and integrated rate laws?
by doing experiments
what does a reaction mechanism describe?
the steps that occur over the course of a rxn
what is the difference between an intermediate product and a catalyst?
an intermediate gets made and then consumed during the elementary reactions. Catalysts don’t get consumed by the reaction
what does a basic reaction rate depend on (mathematically)?
The disappearance of reactants or the appearance of products with respect to time, given by the reaction’s stoichiometry
what does the Arrhenius Equation relate?
Relates quantities of collision model: frequency factor, activation energy, and k constant AT A GIVEN TEMPERATURE
what does Beer’s Law state?
Says the absorption of radiation (at a given wavelength) by a substance is proportional to the solution’s concentration
We used this concept with the spectroscope in biology class when she shined the light on the reaction to measure the enzyme activity in the starch
what is a ‘rate law’ rate expression?
a mathematical expression that describes rate of rxn in terms of concentrations and time
Do reaction rates get faster or slower over time?
they get slower over time as reactants start to run out (evidenced by decreased reactant concentration)
what kind of graph results from a zero order plot of [M] vs time?
a straight line going down
what range of k constant values indicate that a reaction is relatively slow?
values smaller than 10^9
which type of reaction rate expression employs INITIAL rates?
rate laws and integrated rate laws
what is an Active site?
The complex on an enzyme where catalysis is facilitated
how do catalysts reduce activation energy?
by introducing an alternative rate reaction for the overall/net reaction
what is an Intermediate ‘product’ in a rate mechanism?
Temporary/intermediate product created during a former elementary rxn/step that gets consumed in the process of the rxn progressing to the next elementary rxn/step
what branch of mathematics explains the expressions for rate laws and rate orders?
calculus
what kind of graph results from a second order plot of 1/[M] vs time?
straight line going UP
what does the Lock and Key model for enzymes describe?
The idea that substrates bind to enzymes at specific active sites in order to initiate the rxn
what 2 factors are k constants generally dependent upon?
temperature
presence of catalysts
What is an activated complex?
The region between/around molecules/compounds that are about to bond in a reaction
Occurs when the rxn molecules/compounds are in a high energy/transition state; about to react
what kind of graph results from a first order plot of ln [M] vs time?
a straight line gown down
how are the rate laws for elementary reactions determined?
by their molecularity: The number of REACTANT molecules present during a given step/elementary rxn of an overall chemical rxn
what are the units for a second order reaction’s rate constant?
M-1 s-1 or 1/M*s
what are Substrates?
What you call the reactants that enzymes act on
What are the three ways to mathematically describe the rate/speed of a chemical reaction?
(basic) Reaction rate
Rate Law
Integrated rate law
what does a reaction rate quantify?
the speed at which a chemical reaction occurs
what is a Rate determining step (of a rxn mechanism)?
The slowest in a series of rxn elementary steps
Sets the pace for the entire over arching rxn; often involves intermediate ‘products’
what are Enzymes?
biological catalysts that facilitate ‘catalysis’ (speed up reactions) in living things
what is a Homogenous catalyst?
A rxn catalyst that is in the same phase as the reactants
what kind of graph results from a first order plot of [M] vs time?
some kind of downward curve
what is Activation energy?
the Minimum energy required for a rxn to occur
