Topic 8 Chemical Kinetics Flashcards
What does chemical kinetics study?
The rate at which a chemical process occurs
It also provides insight into the reaction mechanism.
What are the factors that affect reaction rates?
- Concentration of reactant
- Temperature
- Catalyst
- Agitation (mixing)
- Choice of reactant
- Surface area
How does concentration affect the rate of a reaction?
As the concentration of reactants increases, the likelihood of reactant molecules colliding also increases.
What effect does temperature have on reaction rates?
At higher temperatures, reactant molecules have more kinetic energy, move faster, and collide more often and with greater energy.
What is a catalyst?
A substance that changes the speed of a chemical reaction without undergoing a permanent chemical change itself.
How do catalysts increase the rate of a reaction?
By decreasing the activation energy of the reaction.
What are the two types of catalysts?
- Homogeneous Catalyst
- Heterogeneous Catalyst
What is the activation energy?
The minimum amount of energy required for a reaction to occur.
What is the Arrhenius equation?
k = A e^(-Ea/RT)
where k is the rate constant, A is the frequency factor, Ea is the activation energy, R is the gas constant, and T is the temperature in K.
What does the rate constant (k) depend on?
The rate constant is independent of concentration but varies with temperature.
What is the relationship between reaction rate and concentration?
Reaction rate is defined as the change in concentration of a reactant or product per unit time.
What is a rate law?
An equation that describes the relationship between reactant rates and reactants concentration.
What does the reaction order indicate?
The extent to which the concentration of a species affects the rate of a reaction.
What is the general form of a rate law for a reaction?
Rate = k[A]^m[B]^n
How do you determine the overall order of a reaction?
By adding the exponents on the reactants in the rate law.
What characterizes a zero-order reaction?
Rate = k, which is independent of concentration.
What is the relationship between stoichiometry and reaction order?
There is no simple correlation; the values of m and n in the rate law must be determined experimentally.
True or False: The rate of a reaction is always positive.
True
How is the instantaneous rate of a reaction determined?
By taking the slope of a tangent line to the concentration versus time curve.
What is the significance of the activated complex in a reaction?
It represents the arrangement of atoms at the top of the energy barrier during a reaction.
What happens to the rate of reaction as time progresses?
All reactions slow down over time.
What does the slope of a concentration vs. time plot indicate?
The instantaneous rate at that time.
Fill in the blank: The reaction order is the exponent to which the concentration of that species is raised, and it indicates to what extent the concentration of a species affects the rate of a reaction, as well as which species has the greatest effect. This is referred to as the _______.
reaction order
What is the rate law for a first-order reaction?
Rate = k[A]
where n = 1
What is the rate law for a second-order reaction?
Rate = k[A]^2 or Rate = k[A][B]
where n = 2
How can the effect of concentration on rate be summarized?
Rate is proportional to the concentration terms raised to their respective orders.
What does it mean if the order of reaction is zero?
The rate is constant and does not depend on the concentration of reactants.
What is the rate law for a 0th order reaction?
Rate law: Rate = k
Where n = 0
What is the graphical representation of a 0th order reaction?
Concentration vs. Time graph is a straight line
Y axis: Concentration, X axis: Time
What is the rate law for a 1st order reaction?
Rate law: Rate = k[A]
Where n = 1
What is the graphical representation of a 1st order reaction?
ln(Concentration) vs. Time graph is a straight line
Y axis: ln(Concentration), X axis: Time
What is the rate law for a 2nd order reaction?
Rate law: Rate = k[A]^2 or Rate = k[A][B]
Where n = 2
What is the graphical representation of a 2nd order reaction?
1/(Concentration) vs. Time graph is a straight line
Y axis: 1/(Concentration), X axis: Time
How can the order of a reaction be determined?
The order is an experimental value or is provided in the problem statement
It may also be explained through the relationship of concentration and time.
What is the definition of half-life in relation to a reactant?
The time required for a reactant to reach half its original concentration
Denoted as t1/2.
What is the formula for half-life of a first order reaction?
t1/2 = 0.693 / k
Where k is the rate constant.
What is the formula for the rate of a first order reaction given concentration and rate constant?
Rate = k[A]
Example: If k = 2.9 x 10^-6 s^-1 and [A] = 0.85 M, then Rate = k[A].
What is the rate law for a second order reaction given the concentrations of A and B?
Rate = k[A][B]
Example: If k = 4.2 x 10–5 M–1 s–1, [A] = 0.52 M, and [B] = 0.69 M.
Fill in the blank: The decomposition of ethanol at 600K showed a plot of ______ versus time resulting in a straight line.
Concentration
This indicates a specific order of reaction.
What is the relationship between the slope of a line in a concentration vs. time graph and the rate constant?
The slope corresponds to the rate constant for the reaction
If the graph is linear, it indicates a specific order of reaction.
Fill in the blank: The half-life for a second order reaction can be calculated using the initial concentration of ______.
Butadiene
Example: If the initial concentration of butadiene is 0.005 M.
