Reaction Rates Flashcards
(17 cards)
Equation for finding rate
r = k[A]^m [B]^n
What does each letter in the rate equation mean?
r = rate
k = rate constant
A = reactant
B = reactant
m & n = reaction orders
What is zero order?
Concentration has no effects of rate of reaction
What is first order?
Concentration and rate of reaction are directly proportional (rate increases by same amount concentration increases)
What is second order?
Rate of reaction is proportional to concentration squared (r = k[A]^2)
Eg. If A doubles (x 2), rate will increase by 4 (2^2)
Effect of temperature on k
Increased temperature –> increased k value
Describe the clock reaction
1) Hydrogen peroxide and iodide ions react to form iodine
2) Thiosulfate ion immediately reacts with iodine formed
How can initial rate of the clock reaction be found?
Measure the time it takes for reaction to turn blue/black
How do you determine the order of the clock reaction?
Repeat experiment using different concentrations of reactants
How do you work out rate from a graph?
Y = mx + c (Log rate = log k + n log[Y])
n = gradient –> (change in y) / (change in x)
Log k = y-intercept
What are the 2 ways to write the Arrhenius equation?
k = Ae ^-Ea/RT
ln k = ln A - (Ea / RT)
Rearrange the Arrhenius equation to make A the subject
A = (k) / (e^-Ea/RT)
Rearrange the Arrhenius equation to find Ea
Ea = (ln A - ln k) x RT
Rearrange the Arrhenius equation to find T
T = Ea / (ln A - ln k) x R
How do you workout activation energy from a graph?
1) Find the gradient (change in y / change in x)
2) Ea = -gradient x R (Remove the minus sign from the answer after)
3) Convert answer to kJ (divide by 1000)
What characterises the rate determining step?
The slowest step
