Chapter 14 - Kinematics

Question 1

what are reaction rates?

Answer 1

The relationship among reaction rates and stoichiometric coefficients can be applied to any reaction

Reaction Rate = -1/aΔ[A]/Δt = -1/bΔ[B]/Δt = 1/cΔ[C]/Δt = 1/dΔ[D]/Δt

• reaction rates are negative for A and B because they are being lost and C and D are being produced that is why they are positive
• reaction rates unit is always M/t

Question 2

What are differential Rate Laws?

Answer 2

reaction rates can also be described using algebraic expression called a differential rate equation
- A rate law links the rate of a reaction with the concentrations of REACTANTS through a rate constant (k)
Rate = k[A]^y[B]^z

Question 3

what are reaction orders?

Answer 3

These exponents (y and z) in the rate law or equation are called orders of reaction

Question 4

what is a first order reaction?

Answer 4

If the value of an exponent is 1 the reaction is directly proportional to the concentration of that species

Question 5

what is a second order reaction?

Answer 5

If the value of an exponent is 2, the reaction rate is directly proportional to the square of the concentration of that species

Question 6

what is the overall order of the reaction?

Answer 6

The sum of the exponents is known as the overall order of the reaction

Question 7

The units of k depend on what?

Answer 7

The units of k depend on the 1 minus overall order of reaction

Question 8

what are the units for k if the overall order of reaction is zero?

Answer 8

M*s^-1

Question 9

what are the units for k if the overall order of reaction is 1?

Answer 9

s^-1

Question 10

what are the units for k if the overall order of reaction is 2?

Answer 10

M^-1*s^-1

Question 11

what are the zero, first and second order rate laws?

Answer 11

Integrated rate laws and half-lives can be determined for other reaction orders

Question 12

what is the zero order integrated rate law and half life?

Answer 12

Differential Rate = k[A]^0
Integrated Rate Law = [A] = [A]o - kt
Half-Life = t1/2 = [A]o/2k

Question 13

what is the first order integrated rate law and half life?

Answer 13

Differential Rate = k[A]^1
Integrated Rate Law = ln[A] = ln[A]o -kt
Half-Life = t1/2 = ln(2)/k

Question 14

what is the second order integrated rate law and half life?

Answer 14

Differential Rate = k[A]^2
Integrated Rate Law = 1/[A] = 1/[A]o + kt
Half-Life = t1/2 = 1/k[A]o

Question 15

what is the rate of decay and carbon dating?

Answer 15

• It is always the 1st order
• Its formulas are identical to the first order integrated rate law and half life formulas just rearranged

ln(N/No) = -kt
k = 0.693/t1/2
A = k*N

A - Number of disintegrations per unit time
k - decay (rate) constant
N - number of nuclei present at a given time

Question 16

what is the Transition State Theory?

Answer 16

in the transition state theory, a hypothetical species is believed to exist between the reactants and the products called the ACTIVATED COMPLEX

Question 17

What is a reaction profile?

Answer 17

energies are plotted and the vertical axis against a quantity called “progress of reaction” on the horizontal axis

Question 18

what is activation energy?

Answer 18

the energy above the reactant, thermal energy that is required to reach the activated complex

• the difference in energy between the reactants and products is labelled ΔEreaction (which doesn’t change because it is a state function)

Question 19

the higher the activation energy the….?

Answer 19

the higher the activation energy the slower the reaction rate
ln(k) = ln(A) - Ea/RT
k = A*e^-Ea/RT (k inversely proportional to activation energy)
R = 8.3145

Question 20

the lower the activation energy the…..?

Answer 20

the lower the activation energy the faster the reaction rate
ln(k) = ln(A) - Ea/RT
k = A*e^-Ea/RT (k inversely proportional to activation energy)
R = 8.3145

Question 21

what is The Arrhenius Equation?

Answer 21

the value of the rate constant for a particular reaction depends on the activation energy of the reaction, the temperature of the system, and how often a collision occurs in which the atoms are in the required orientation

ln(k2/k1) = -Ea/R*(1/T2 - 1/T1)
R = 8.3145

Question 22

what is Steady State approximation?

Answer 22

• Fast reversible step followed by a slow second step
• Use the coefficients of the slow step and not the balanced equation
• You only determine the rate of the slow step, so therefore you use the slow step as the overall rate of reaction
  -Thinking rate = k[N2O2][O2]
• but recall N2O2 is an intermediate, so write it in terms of its reactants
  SO NEW RATE = k[NO]^2[O2]

Question 23

what is a heterogeneous catalyst?

Answer 23

refers to the form of catalysis, where the catalyst is present in a different phase of matter than are the reactants and products

(ie. catalyst is gas, reactants and products liquid)

Question 24

what is a homogeneous catalyst?

Answer 24

catalytic reactions where the catalyst is in the same phase as reactants and products