Module 5 Flashcards
What is a zero order reaction?
Concentration doesn’t influence the rate of the reaction.
So no matter how much the concentration changes, the rate isnt changed
What is a first order reaction
The rate of reaction is directly proportional to the concentration of the reactant that the reaction is first order with respect to.
What is a second order of reaction?
The rate of reaction is directly proportional to the concentration of the reactant SQUARED
Generally how do you write a rate equation?
Rate = k x ([A]^n) x ([B]^m) for all reactants
Where [] means the concentration of
k is a constant (which you need to work out probably)
And m & n are the orders with respect to each reactant individually
How do you work out the units of the rate constant for a particular rate equation
Set the rate equation equal to k and then use dimensional analysis
ie the units for the rate is moldm^-3s^-1
And the units for the concentration is moldm^-3
How can you determine orders of reaction from the initial rate of a reaction?
Questions will give you a table which varies concentrations of some reactants and it shows the initial rate
So if you double the concentration of a reaction and that doubles the rate, then it’s first order, for example.
How can you monitor the rate continuously?
Plot a graph of concentration against time
You would use something to measure the progress of a reaction eg gas collection, mass loss, colour change, etc
How do you monitor the progress of a colour changing reaction continuously?
How does it work?
Use a colorimeter
Measures the intensity of light passing through a sample
Filter is chosen so that it’s a complimentary colour to the colour being absorbed. Absorbance is directly proportional to the concentration of the solution
How do you tell the difference between a first order and second order graph?
You’d have to work out the half life
If it’s constant, then it’s first order
If not, it’s second order
How do you determine K for a first order reaction?
Method 1: drawing tangents, sub the concentration and rate into the rate equation
Method 2: use the half life
k= ln2/t1/2 (half-life)
How do you find the initial rate from a graph?
Tangent at t = 0
Or if you find the time taken for an observed visual change to occur, do 1/time
What is meant by the rate determining step
The slowest step in a multi-step reaction is the one which determines the rate of the overall reaction
Define partial pressure
Contribution that a gas makes to the total pressure
Define mole fraction
The number of moles of a particular gas compared to the total moles of all gases in a mixture
What does a K value of 1 indicate about the equilibrium?
Equilibrium halfway between reactants and products
