Chapter 17 Flashcards
Kinetics
Chemical Kinetics
Study of reaction rates, how change under varying conditions, and which molecular events occur during a reaction
Reaction rate
How quickly the concentration of reactants/products change over time.
What is the rate equation for the disappearance of a reactant
Rate = -∆[A]/∆t
[A] = Concentration of A/reactants
∆t = Change in time
**Rate is always positive, this is why the numerator is -∆
What is the rate equation for the appearance of a product
Rate = ∆[B]/∆t
[B] = Concentration of B/products
∆t = Change in time
What is the rate law equation?
Rate = k[A]^x[B]^y
k = rate constant
x = Order of RXN with respect to A
y = Order of RXN with respect to B
Orders of RXN
0th = Substance has NO effect on rate
1st = reaction is directly proportional to the concentration of substance
2nd = reaction is proportional to the squared concentration of substance [2]^2 = 4 (reaction rate is 4)
Method of initial rates
Determines the rate of reactions. Must know the rate, but then can vary the concentrations of the reactant(s) to monitor their rate of dissapearance – which will give us the order of RXN.
Integrated rate law for 0th order
[A]vt = -kt + [A]v0
v = next number is a subscript
**Rate constant can’t be negative, so it is the absolute value k = |m|
Integrated rate law for 1st order
ln[A]vt = -kt + ln[A]v0
v= next number is subscript
Integrated rate law for 2nd order
1/ ([A]vt) = kt + 1/([A]v0)
v = subscript
How do you use integrated rate law to find which is the correct reaction order?
Graph all 3 equations, then find the most linear. This represents the reaction order (most linear = highest R2 value)
What are the rate constant (k) units?
1st order = s^-1
2nd order = s^-1/M
0th order = Ms^-1
Half life equation for 0th order
([A]v0) / 2k = t
Half life equation for 1st order
(ln(2))/k = t
Half life equation for 2nd order
1 / ([A]v0 * k) = t
