Topic 6: Kinetics

Question 1

Collision theory: for a reaction between two particles to occur, what conditions must be met?

Answer 1

Particles must collide, and they must collide w/ appropriate geometry/orientation and enough energy to bring about the reaction

Question 2

What is chemical kinetics?

Answer 2

Study of the factors affecting the rate of a reaction

Question 3

What is the definition for the rate of a chem rxn?

Answer 3

The change (decrease/increase) in concentration of products/reactants per unit time

Question 4

How can concentration changes in a reaction be monitored indirectly?

Answer 4

Change in volume of a gas, mass, concentration using titration, pas pressure, conductivity, calorimetry, light absorbance

Question 5

How are the results of measuring concentration change usually represented? What does the slope of the graph represent?

Answer 5

Plotted in a graph of concentration against time. The slope of the graph is change in concentration over change in time, and it represents the rate at that point

Question 6

When will the rate of rxn be steepest generally? Why?

Answer 6

Start of the curve because that’s when the concentration of the reactant particles is highest; collisions are more frequent

Question 7

Why does rate of rxn decrease over time?

Answer 7

Concentration of reactants decreases, so collisions decrease

Question 8

How do you calculate rate of disappearance of reactants?

Answer 8

• delta [R] / delta T
  The negative change in the reactant concentration over the change in time

Question 9

How do you calculate the rate of the formation of products?

Answer 9

delta [P] / delta T
Change in concentration of products over change in time

Question 10

What are four ways to affect the rate of a reaction?

Answer 10

Surface area, temperature, concentration, pressure

Question 11

How does surface area affect rxn rate?

Answer 11

Increased SA through breaking apart a compact, large molecule increases rxn rate because more collisions can occur

Question 12

How does temp affect rate of rxn?

Answer 12

increased temp increases rxn rate because particles move faster, collisions are more frequent, more particles have necessary activation energy.

Question 13

Generally, how does an increase of 10 C affect rxn rate?

Answer 13

Doubles rate of rxn

Question 14

How does concentration affect rate of rxn?

Answer 14

Increased concentration means increased rxn rate because more particles are present

Question 15

How does pressure affect rate of rxn?

Answer 15

Increased pressure increases rate of rxn because it compresses the gas, so there is technically an increased concentration, so more collisions per second

Question 16

What does a Maxwell-Boltzman Distribution curve show?

Answer 16

Distribution of kinetic energy for a reaction. Y axis is number of particles, x axis is energy

Question 17

Generally, do a large or small number of particles have the required activation energy for the reaction to occur?

Answer 17

small

Question 18

What changes are present in a MBD curve as temp increases?

Answer 18

More particles have a high velocity, so the avg. kinetic energy increases, allowing the curve to broaden. Activation energy and total area under the curve stay the same

Question 19

How does adding a catalyst work?

Answer 19

It reduces the activation energy, so more particles have the energy required to react?

Question 20

How can you tell if a species is a catalyst?

Answer 20

It will likely show up on both the product and reactant side.