Rates Of Reaction Flashcards
How are reaction rates measured?
Changes in the quantities of reactants or products over times
What is the rate equation?
Rate = k [A]order[B]order
What happens when you change the concentration in a reaction?
Changes the rate of reaction
What is first order?
The concentration of a reactant is directly proportional to the rate
What is zero order?
When the concentration of a reactant has no effect on the rate?
What is second order?
The rate of reaction is increased by the amount that the concentration was increased squared
What does the overall order of a reaction give?
The overall effect of the concentrations of all reactants on the rate of reaction
How is the overall order calculated?
Overall order = sum of orders
What are two methods of continuous Monitoring of a reaction that produces gas?
Monitoring by gas collection
Monitoring by mass lost
What does a colorimeter do?
Measure the intensity of light passing through a sample
A filter of a complementary colour is chosen to the colour absorbed in the reaction
Outline a reaction for determining concentration using a colorimeter
Prepare standard solutions of known concentrations
Zero colorimeter with water
Measure absorbance of standard solutions
Plot calibration curve - absorbance against conc
Take absorbance of unknown
Compare on calibration curve
What is the gradient of a concentration time graph?
Rate of reaction
What is half life?
Time taken for Half of a reactant to be used up
Describe exponential decay
Constant half life with concentration halving every half life - as in first order reaction
What are the two methods of determining the rate constant from a concentration time graph for first order reaction?
Calculating rate constant from the rate - tangent to curve drawn and gradient calculated giving the rate
Calculating rate constant from half life - k=ln2
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T1/2
What is a clock reaction?
Time from start of reaction to an visual change is observed
Convenient way of obtaining initial rate by taking single measurement
Initial rate is proportional to 1/time
Repeated several times with different conc
What is the rate determining step?
The slowest step in the reaction mechanism
What is the reaction mechanism?
Series of steps that make up an overall reaction
What does the rate equation only include?
Species involved in the rate determining step
What do the orders in the rate equation match?
The number of species involved in the rate determining step
What happens to rate and the constant as temperature increases?
They both increase
What two factors contribute or the increased rate and constant when temp is increased?
Shifts Boltzmann distribution to right increasing proportion of particles that exceed activation energy
As temp increases particles move faster and collide more frequently
What is stoichiometry?
The relative amounts of te species in the reaction
What does the exponential factor in Arrhenius represent?
Proportion of molecules that exceed the activation energy
