Physical Chapter 7: Rate Equations & Kp Flashcards
How do you work out reaction rate from a graph?
Take the gradient
What is the rate equation?
Where A + B -> C + D,
Rate = k[A]m[B]n
where m and n are the orders of reactants.
How do you calculate reactant orders?
if [A] changes and the rate stays constant, the order of A is 0.
If [A] doubles and the rate doubles, the order of A is 1.
If [A] doubles and the rate quadruples, the order is 2. (Rate is proportional to [A]2)
What does a greater value of k mean?
The reaction is faster
What happens to K when temperature increases?
It increases
What is the initial rates method?
You repeat an experiment several times using different initial concentrations of the reactants. Change one at a time, and calculate initial rate for each experiment. Then, compare how initial concentration affects initial rate to work out orders.
What is the rate-determining step?
The slowest step - it will decide the overall rate
What does it mean if a reactant appears in the rate equation?
It affects the rate
What does the order of a reactant tell you about the rate-determining step?
How many molecules of that chemical are involved in rate-determining step
What is the Arrhenius equation?
k = Ae-Ea/RT
Ea = Activation energy (J)
T = Temperature (K)
R = Gas constant (8.31J/K/mol)
A = arrhenius constant
What does an increase in Ea mean for k?
K will decrease - higher activation energy means slower rate
How do we plot the Arrhenius equation?
ln(k) = -Ea/RT + ln(a)
How do you calculate partial pressures?
mole fraction x total pressure
How do you work out mole fractions?
No. of moles of substance/total moles in the mixture
How do you work out Kp?
Where aA + bB = cC + dD,
Kp = (pC)c(pD)d/(pA)a(pB)b
