5.1.1 How Fast? Flashcards
What’s the rate equation
Rate = k [A]^n
What’s the order of the reaction
The power that the concentration of a reactant is raised to
What’s overall order
Overall effect of the concentration of all reactants on rate of reaction
Definition of half life
Time taken for half of a reactant to be used up
Definition of rate-determining step
Slowest step in a multi-step reaction
How does 0 order effect rate
It doesn’t
How does first order effect rate
Rate = k [A]^1
How does second order effect rate
Rate = k[A]^2
Shape of a concentration-time graph for zero order reaction
Straight line with negative gradient
Shape of a concentration-time graph for a first order reaction
Downward curve with decreasing gradient over time
Half life in first order conc-time graph
Constant
Equation involving half life
K= ln2 ÷ half life
Shape of a rate-conc graph for zero order
Horizontal straight line
Shape of a rate-conc graph for first order
Straight line graph through origin, rate is directly proportional to conc
Shape of a rate-conc graph for second order
Upward curve, increasing gradient
How to find rate constant from a first order rate-conc graph
Gradient of the line
How to determine rate via continuous monitoring
Prepare standard solutions of known conc of iodine
Select green/blue filter on colorimeter
Zero colorimeter with water
Measure absorbance readings of the solutions
Plot calibration curve of absorbance against iodine conc
Carry out reaction between propanone and iodine, take absorbance readings at measured time intervals
Use calibration curve to measure conc of iodine at each absorbance reading
Plot graph of concentration of iodine against time, determine order of reaction
How to determine rate via initial rates method
Solution is colourless at beginning and t is measured for blue black colour of starch-iodide to appear
Repeated with different concentrations, another chemical delays colour change, when its all used up, blue-black colour forms
Initial rate proportional to 1÷t
Graph of 1÷ t against conc plotted, shape matched to order
Then reaction done whilst changing conc of a different reactant
How to predict reaction mechanisms
Rate equation only includes reacting species involved in RDS
Orders in rate equation match number of species in RDS
Effect of temperature on rate constant
Increases rate constant with increased temp
Increasing temperature shifts Boltzmann distribution to the right and increases proportion of particles that exceed the activation energy
As temp increases, particles move faster and collide more frequently
Rearranged Arrhenius equation
lnk = -Ea ÷ RT + lnA
