Chapter 14 - Chemical Kinetics Flashcards
What is chemical kinetics?
The area of chemistry in which reaction rates are studied.
What 4 factors affect the reaction rate?
- Physical state of reactants
- Concentration
- Temperature
- Presence of catalysts
How are reaction rates usually expressed?
Molarity/second (M/s).
What generally happens to a reaction rate as time passes?
It slows down.
What is the instantaneous rate?
It is the slope of a line drawn tangent to the concentration-versus-time curve at a specific time.
How is a rate law calculated?
Rate=k[A]^m[B]^n
A and B=molarity
m and n=order of reaction
How do you calculate the overall reaction order?
You add the reaction orders together (m+n=overall).
What is a first order reaction like?
When the rate is proportional to the concentration of a single reactant raised to the first power.
How is a first order reaction calculated?
Rate=k[A]
Integrated rate:
ln[A]t=-kt+ln[A]0
What is a second order reaction?
One for which the overall reaction order is 2.
How is a second order reaction calculated?
Rate=k[A]^2
Integrated rate:
1/[A]t=1/[A]0+kt
What is a zero order reaction?
One for which the overall reaction order is zero.
Rate=k
What is the half-life of a reaction?
The time required for the concentration of a reactant to drop to one-half of its original value.
How is the half-life of a first order reaction calculated?
0.693/k or ln(2)/k
How is the half-life of a second order reaction calculated?
1/(k*[A]0)
What is the collision model?
A model/theory that assumes reactions occur as a result of collisions between molecules.
Briefly describe the relationship between concentration and collisions.
Lower concentration=fewer collisions
Higher concentration=more collisions
What is activation energy?
The minimum energy required for a reaction to occur.
What is the activated complex?
The highest energy arrangement in the pathway from reactants to products.
What is the Arrhenius equation?
k=A*e^(-Ea/RT)
This describes the relationship between k and temperature.
What is the log form of the Arrhenius equation?
ln(k)=ln(a)-Ea/RT
What does a reaction mechanism do?
It details the individual steps that occur in a reaction.
What are elementary reactions?
The steps that make up a reaction mechanism.
What is molecularity?
The number of molecules that come together to react in an elementary reaction.
What is a catalyst?
A substance that increases the rate of a reaction without undergoing a net chemical change itself.
What is a homogenous catalyst?
A catalyst that is in the same phase as the reactants.
What is a heterogeneous catalyst?
A catalyst that has a different phase from the reactants.
What are enzymes?
A globular protein that catalyses a biological chemical reaction.
