Rate Equations Flashcards
Rate of reaction
The change is concentration of a substance in a given time
Units of rate
Moldm-3s-1
Reactions can only occur when…
Collisions take place between particles having sufficient energy
What is the sufficient energy called
Activation energy
Activation energy
The minimum energy required to start a reaction by the breaking of bonds
How does increasing conc increase rate of reaction
- more particles in given volume
- more frequent successful collisions
How does increasing pressure increase rate
- increasing pressure means same particles in a smaller volume
- more frequent successful collisions
How does increasing SA of a solid increase rate
Powders increase SA- more frequent successful collisions
How does increasing temp increase rate
(Maxwell Boltzmann) more particles with energy equal to or greater than Ea so more successful collisions
How does a catalyst increase rate
Provides alternative pathway with lower Ea so far more molecules have Energy equal to or greater than activation energy
what does the rate equation show
the relationship between the rate of a reaction and the initial conc of the reactants
general rate equation
rate= k[A]m [B]n
what is [A] in rate equation
conc of A
what is [B] in rate equation
conc of B
what is m in rate equation
order with respect to A
what is n in rate equation
order with respect to B
what is k in rate equation
rate constant
what is the overall order of a reaction
the sum of the individual orders
half life
the time taken for the concentration of a reactant to half
how would zero order be shown on a conc-time graph
straight line indicating uniform day
how would first order be shown on a conc time graph
curve- equal half lives
how would second order be shown on a conc time graph
steeper curve- half lives increase
what is the gradient at a particular time on a conc time graph a measure of
the rate at that time
how to determine order of ror with a conc time graph
- start with known conc of a and b
- ensure conc of one (b) is much larger than other- remains constant
- determine conc of A at different times
- plot graph
- continuous monitoring method
how can rate-conc graph be plotted
- conc-time graph plotted
- tangents drawn, giving ror values
- rate-conc graph plotted
rate graph zero order
flat line
rate graph first order
straight diagonal line, positive gradient
rate graph second order
curve
what is k
a proportionality constant that links rate of reaction with the concentrations of reactants
correlation between value of k and rate
k larger- faster rate
what do the units of k depend on
overall order of reaction
what do chemical reactions often take place in
a series of steps called the reaction mechanism
what can the rate equation provide clues about
a likely reaction mechanism by identifying slowest stage of a reaction sequence
rate determining step
slowest step in a reaction mechanism
what will any step that occurs after rate determining step not affect
overall rate- reactants involved in later steps wont appear in rate equation
how can you tell if the reaction is a one step process
the powers in the rate equation match the stoicheometry of the overall equation
how can you tell if the reaction has more than one step
the powers of the rate equation don’t match the overall equation
what always increases when temperature is increased
the rate of reaction- Maxwell districution
if the temperature is increased in a reaction, why must k increase as rate increases
if [A] and [B] are kept constant k must increase
rate=k[A]m[B]n
what is the increase of k with temperature
exponential
what is the relationship between rate constant and temp described by and what does it allow us to work out
Arrhenius equation
allows us to work out Ea
the Arrhenius equation
k=Ae^-Ea/RT
what does k mean in Arrhenius equation
rate constant
what does A mean in Arrhenius equation
Arrhenius constant
what does ea mean in Arrhenius equation and units
activation energy (J)
what does R mean in Arrhenius equation
ideal gas constant
what does t mean in Arrhenius equation and units
temperature (K)
how can the Arrhenius equation be rearranged
by taking the natural log (ln) of both sides
Arrhenius equation rearranged
lnK=lnA -Ea/RT
what form can rearranged Arrhenius equation rearranged be expressed in
y=mx+c
how can Arrhenius equation be used to determine the activation energy of a reaction
- k can be determined at different temperatures
- graph poltted with k on y axis and 1/T on x axis
- line of best fit is a straight line and so can be described as y=mx+c
