Chemical Industury Flashcards
Rate of reaction=
The change in the amount of products per unit time
How can you measure the rate of a reaction?
pH change Volume of gas given off Loss of mass Colour change Titration
What is the general rate equation?
rate=k[A]^m[B]^n
What are m and n in the rate equation?
The orders of reaction with respect to A/B
The sum gives the overall order of reaction
What does k represent in the rate equation?
The rate constant- the bigger it is, the faster the reaction. k is affected by temperature- as the temperature increases, k also increases
What are the units of rate in the rate equation?
mol dm^-3 s^-1
How can you work out the units of k?
(mol dm^-3 s^-1)/((mol dm^-3)^m)(mol dm^-3)^n)
How do you work a value for k?
rate/[A]^m[B]^n
What does the order of reaction with respect to a reactant/catalyst tell you?
How the concentration of the reactant/catalyst affects the rate of reaction
What does zero order mean?
Changes to [A] has no effect on the rate of reaction
What does first order mean?
Rate ∝ [A]
If [A] doubles, rate of reaction doubles
What does second order mean?
Rate ∝ [A]^2
If [A] doubles, rate of reaction quadruples
Define ‘half-life of a reactant’
The time it takes for half the reactant to be used up
How can the order of reaction by worked out by looking at the shape of [reactant]-time graphs?
By seeing if the half-life is constant. If the half-life decreases as time goes on, it is zero order. It’s first order if the half-life remains constant. If the half-life increases, it’s second order
How can k be worked out from first order reaction graphs?
k=(ln2)/half life
What is the Arrhenius equation?
k=Ae^(-Ea/RT)
Where A is the pre-exponential factor, Ea is the activation enthalpy in J/mol, T is the temperature in K, and R is the gas constant (8.31 J/K/mol)
Why does k get smaller as Ea gets bigger?
A higher activation enthalpy makes it less likely for successful reactions to take place
What is the rate determining step?
The slowest step in a multi-step reaction
What does it mean if a reactant/catalyst appears in the rate equation?
They are involved in the rate determining step
What determines the overall rate of a reaction?
The rate of the slowest step
Why can you predict the rate determining step from the rate equation?
You know what reactants are involved and the number of moles (the order of reaction with respect to reactant= number of moles)
