rates of reaction Flashcards
How are reaction rates measured
- by observing the changes in the quantaties of reactants or products over time
What are the equations for rate of reaction
- quantity reacted or produced/time
- change in concentration/time
what is the unit for rates
moldm-3s-1
what does the power represent for each reactant
order of reaction
what are the common orders
- zero
- first
- second
What is zero order
when the concentration of a reactant has no effect on the rate
what happens in a zero order reaction
- any number raised to the power zero is 1
- concentration does not influence the rate
what is the first order
a reaction is first order respect to a reactant when the rate depends o its concentration when raised to the power of 1
What is a first order reaction
- if concentration is doubled the reaction rate increases by a factor of 2
- if concentration is triples the reaction rate increases by a factor of 3
What is second order
a reaction is second order with respect to a reactant when the rate depends on its concentration raised to the power of 2
What happends in a second order reaction
- if concentration is doubles the reaction rate increases by a factor of 4
- if concentration is triples the reaction rate increases by a factor of 9
What is the rate equation
the rate equation fives the mathematical relationship between the concentrations of the reactants and the reaction rate
What is the rate constant k
- is the proportionality constant it is the umner that mathematically converts the rate of reaction and concentration and orders
What is the overall order
- the overall order of a reaction gives the overall effect of the concentrations of all reactats on the rate of reaction
- sum of orders with respect to each reactant
How do you solve the units of the rate constant k
- rearranging the equation to make k the subject
- substitute units into the expression for k
- cancel common unit and show the final units on a single line
What is the initial rate
the initial rate is the instantaneous rate at the beginning of an experiment t=0
How can concentration time graph be plotted
- from continuous measurement taken during the ccourse of a reaction - continuous monitoring
How can you monitor reactions that produce a gas
- monitoring by gas collection
- monitoring by mass loss
How can you monitor a reaction that does not produce gas and how
- colour change
- by eye or monitored with a colorimeter
How is a colorimeter used to detect rate of reaction
- measures the wavelengthh of the light passing through a coloured solution is using a filter. the amount of light is absorbed by a solution is measured
How can you tell the rate of reaction from a concentration time graph
measure the gradient
Describe the concetration time graph for zero order
- produces a straight line with a negative gradient
- reaction rate does not change at all during the course of the reaction
- value of the gradient is equal to the rate constant k
Describe the concentration time graph for first order
- a first order reaction produces a downward curve with a decreasing gradient over time
- as gradient decreases with time the reactopm gradually slows down
- the time or the concentration of the reactant to halve is constant
- this is called half life
- rate constant can be determined using it value
Describe the concentration time graph for second order
- downward curve
- steeper at the start
- tailing off more slowly