5.1.1 kinetics
No description yet. This curated deck is ready for daily study.
Card preview (22)
give the equation for finding out k in a first order reaction
k=ln2/t1/2 (half-life) units are s^-1
give the definition of rate of reaction
the change in concentration of a substance in unit time
in a concentration vs time graph how can gradient be worked out
gradient=curve plot a tangent and use y/x to work it out
how can the total order of a reaction be worked out
by adding all the individual orders together
give the arrhenius equation
k=Ae- Ea/RT
give another way that the arrhenius equation that is used
lnk=- Ea/R x 1/t + lnA aka y=mx+c can also be used as lnk= -Ea/RT + lnA
how can the gradient be worked out from the arrhenius equation
gradient = - Ea/R or Ea= gradient x r
how can lnA be calculated from one data point
lnA=lnk - (gradient x 1/t) A=e^lnA
how do clock reactions work
a sudden colour change is observed when the products react with the indicator once it is no longer being used up
what happens during a clock reaction
the change in concentration of reactants is very small over the time period of the reaction temperature stays constant at the end point the reaction has not proceeded too far
give two reasons why it is unlikely a reaction can take place in one step
the rate equation doesn’t match the overall equation collision is unlikely with more than two ions
describe a method more efficient than continuous monitoring
• initial rate method where you time how long it takes for a set amount of product to form for different concentrations of reactant • this means you wont have to monitor several experiments and graphs
what is zero order
rate is unaffected by changes in concentration
what is first order
rate doubles as concentration doubles
second order
rate quadruples as concentration doubles
explain the effect of temperature on k and rate
• k=Ae • k is proportional to rate • if temperature increases the k increases • as k is proportional to rate this means rate also increases
explain the effect of the use of a catalyst on k and rate
• a catalyst lowers Ea so k is increases - k is proportional to rate so rate also increases
what is a half-life
the time it takes for half of a reactant to be used up
how can half lives indicate first order
if they are constant
How can A be calculated from lnA
e^A
give the equation for rate an rearrange to make k the subject
r=k[X]^n[Y]^m k=rate/[X]^n[Y]^m
what is the rate determining step and how does it affect the rate equation
• the slowest step in a reaction that the overall rate depends on • any reactant that occurs in or before the rate determining step appears in the rate equation • intermediates do not go into the rate equation but catalysts do