Rate equations Flashcards
Rate equation
Rate = K [A]order [B]order
Define order of a reaction
The power to which the conc of its reactant is raised in the reaction rate
If [A] changes + rates stays the same
What is the order?
0
If the rate is proportional to [A]
What is the order?
1
If the rate is proportional to [A]2
What is the order?
2
How do you work out the overall order of a reaction?
Add up the orders
How do you find the orders of a reaction?
Experiments
If the value of K inc, what effect does it have on the reaction?
Faster reaction
What happens to K if you inc the conc of reactants?
Stays the same
What happens to K if you inc the temperature?
- K inc
- Conc + orders stay the same
What is the unit of K?
mol dm-3 s-1
Define the initial rate of reaction and how to work it out
- Rate at start of reaction
- Conc-time graph, calculate gradient of tangent at time=0
Suggest why initial rates are used to determine orders?
Conc are known
How do you work out the rate equation?
- Initials rate method:
- Repeat experiment using diff. initial conc reactants
- Calculate initial rate for each experiment
- Work out how initial conc affects initial rate
Define conitinious monitoring
- Way to measure ROR
- Following reaction til end by recording amount of product you have at regular interval
- Used to work out how rate changes over time
If a reaction mechanism has a series of steps, what is the overall rate dependent on?
Rate of the slowest step - Rate determining step
What does it mean if a reactant appears in the rate equation?
- Must affect rate
- Involved w/ rate determining step
Can catalysts appear in the rate equation?
Yes
What does the order of a reaction show?
No. molecules involved in RDS
What does the Arrhenius equation show?
How the rate constant varies w/ temp + Ea
Arrhenius equation
k = Ae -Ea/RT
ln k = ln A - Ea/RT
- k: rate constant
- Ea: activation energy (j)
- T: temp (K)
- R: gas constant
- A: arrhenius constant
What is the formula to work out the activation energy using the arrhenius equation?
Ea = (ln A - ln k) x RT
What happens to k when Ea inc?
- Dec
- Less particles have enough energy to react, less collisions = slower rate
