1.9 - Rate Equations Flashcards
Define the term rate of reaction
Change in concentration per unit time.
State what is being monitored (usually production of a product)
At a given instant, how could you calculate the rate of reaction?
Rate of reaction = change in concentration / change in time
How could you measure the rate of reaction experimentally?
Use a colorimeter a suitable intervals, if there is a colour change.
If gas is involved, use a gas syringe to collect volume of gas evolved or measure the change in mass of the reaction mixture
How would you measure reaction rate for really fast reactions?
Use a flash of light to break bonds use probe flashes to record amount of light absorbed by species. This can show its concentration.
How can you determine the rate constant and rate expression for a reaction?
Only experimentally
What affect the value of the rate constant forgiven reaction?
Temperature
Do you species need to be in the chemical equation to be in the rate expression?
No – species in the chemical equation may be excluded in species, not in the chemical equation may be included
Define the term order of a reaction with respect to given product
The power, to which a species concentration is raised in the rate equation
Define the term overall order of reaction
The sum of the orders of reaction of all species in the rate expression
How could you find the right expression using the initial rate method?
Do a series of experiments, during which you vary concentrations of the concentration of just one reactants changes each time.
When does the starch turn blue black colour in an iodine clock reaction and why?
When all of the Na2S203 has been used up and so I2 is produced which reacts with starch leading to a blue black colour
How can you calculate the rate of reaction from the data from an iodine clock reaction?
Record time taken for colour to change. Use rate = 1/t. This is effectively the initial rate
What is true of the half life of a first order reactant?
Half life is constant
What is the Arrhenius equation?
K = Ae^(-Ea/RT)
K = rate constant
A = pre- exponential factor
R = gas constant
T = temperature in kelvin
Ea = activation energy in joules
What is the rate determining step?
The slowest step in a reaction mechanism, which determines the overall rate of reaction
