Chemical Kinetics

What is chemical kinetics?

The study of how fast chemical reactions happen

What is the rate of a reaction?

A measure of how the reaction progresses over time

What happens as chemical reaction proceed?

The concentrations of products increase

How can you measure the rate of a reaction?

Measured as the change in concentrations of either reactants or products over time

What does the rate expression express?

The change in concentrations of either reactants or products over time

What is the general rate expression for a general chemical equation?

What are all the terms in this called?

Equivalent rate expressions

Where is the negative sign used for the crate expressions?

Used for the reactants ONLY because it is being taken from and decreasing over time

Species with large coefficients do what to concentrations?

They change concentrations more quickly in the reaction

What do relative rate expressions do?

Show how fast reactants and products disappear relative to one another

What are rate laws used for?

To show how changing the concentration of reactants impacts the rate of reaction

How would a rate law look like from this reaction?

• Products are EXCLUDED from rate law expressions

Why are products excluded from rate law expressions?

Because product concentrations do NOT influence the reaction rate

What is k?

The rate constant

The rate constant, k, is ______________ and unique to each reaction/

Temperature-dependent

Reaction order is equal to….

m + n

What does the reaction order do?

Determine how the concentration of a species affects the rate of reation

What does it mean for a reaction to be zero-order?

The rate is constant and does not depend on the concentration of the reactant

What does it mean for a reaction to be first-order?

The rate is directly proportional to the reactant concentration

What does it mean for a reaction to be second order?

The rate is proportional to the square of the reactant concentration

What is the rate reaction for a zero order reaction?

rate = k[A]⁰

What is the rate reaction for a first order reaction?

rate = k[A]¹

What is the rate reaction for a second order reaction?

rate = k[A]²

What is the purpose of integrated rate laws?

They show how concentration changes over time

Which graph is this?

Second order

What graph is this?

Zero order

What graph is this?

First order

What is the slope of a straight line graph equal to?

k

When is half life concentration be determined?

When all the reaction orders are plotted with the same axes

What is the half life of a reaction measuring?

The time it takes for half the remaining ractants to be depleted

What does a half life zero-order reaction graph look like?

• Linear with downward slope

• Reaction will keep going at the same rate no matter what the reactant concentration is

  • Half life decreases as reactant concentration decreases

What is the half life equation for a zero order graph?

What does a half life first-order reaction graph look like?

• Graph is downward sloping with a cruved line

• As reaction progresses, same length of time is required to deplete half od the reactant concentration

  • Half life does NOT change as the reaction goes on

What is the half life equation for a first order graph?

What does a second order graph look like?

• Graph is downward slope with a cruved line

• The reaction slows down more and more as reactant concnetration is depleted

  • The half life increases as the reaction progresses

What is the half life equation for a second order graph?

How does the equation of a line y=mx+b correlate here?

What is the change of enthalpy?

The difference in energy between reactants and products

Exothermic reactions have what kind of ΔH? And what does it mean?

Exothermic reactions release energy and have a negative ΔH meaning that there is more energy in the products than the reactants

So if theres more energy in the reactants than the products, which is more stable?

The products

Endothermic reactions have what kind of ΔH? And what does it mean?

Endothermic reactions have a positive ΔH. This means that the productsd are higher energy than the reactants

If the products and reactants have the same energy, what does this mean?

ΔH = 0 and the reaction is isenthalpic

What does this sign mean?

Denotes the transition state

What is the transition state also known as?

The activated complex

What point on a reaction coordinate diagram has the highest energy?

The transition state

What does it mean that the transition state has the highest energy?

It is the least stable point in the process

Can transition states be isolated?

NO

What is E_a?

This is the forward activation energy that is the energy difference btween the reactants and the transition state

Amount of energy needed for the reaction to happen

What is the rate--determining step?

The step that occurs the slowest or the step with the highest activation energy

What are intermediates?

Complexes briefly formed in between reactants and products

They’re stable, not like transition states, and so they last longer

Does reaction pathway change/influence the change in enthalpy?

NO

What are the qualities of a catalyst?

• Not consumed so they will be on both sides of the equation

• Lower activation energy

• Don’t speed up reactions by changing energy

• Provide alternative reaction pathway

  • Don’t shift equlibrium

For a chemical reaction is happen, what conditions have to be met?

• Molecules must physically collide

• Molecules must have enough energy to react

  • Molecules must collide in the proper 3D orientation

What does increasing temperature do in terms of the Arrhenius equation?

Raises particle kinetic energy which will lead to more collisions and higher probability that each collision has enough energy to reach the activation energy

If the activation energy of a reaction and the temperature are both doubled, what will happen to the rate of reaction?

A. The rate will double

B. The rate will quadruple

C. The rate will be cut in half

D. The rate will be cut by three quarters

E. The rate will not change

The rate will not change

How would you find the overall rate law of a reaction coordinate diagram?

What is the hallmark of an intermediate species?

You must find it on BOTH sides of the reaction in equal quantities.

What is the rate constant for a zero order reaction?

M¹s^-1

What is the rate constant for a first order reaction?

s^-1

What is the rate constant for a second order reaction?

M^-1s^-1

What happens to the rate os a reaction over time?

It decreases because the rate of a chemical reaction depends on the concentration of the REACTANTS

If the reactants are decreasing as a reaction proceeds then so will the rate

What is radioactive decay?

Spontaneous reaction where unstable nuclei transform into more stable ones by emitting radiation

Each atom decays on its own

Radioactive decay follows which type of reaction kinetics?

First order kinetics

How do you calculate the average rate of disappearance?