Rates of Reactions

Question 1

What is the definition for the rate of reaction?

Answer 1

It is the change in the amount of the concentration of the reactant per unit time.

Question 2

What is catalysis?

Answer 2

It is the process of changing the rate of a

chemical reaction by the action of a catalyst.

Question 3

What is a catalyst?

Answer 3

It is a substance that alters the rate of a chemical
reaction but which is not used up during the reaction,
and which is chemically unchanged at the end of it.

Question 4

What is activation energy?

Answer 4

It is the minimum amount of energy
which colliding molecules must have before they can
react together.

Question 5

What is the instantaneous rate?

Answer 5

It is the rate at a particular point in

time during the reaction.

Question 6

What is the average rate?

Answer 6

It is the total time for reaction to go to

completion.

Question 7

What is the three steps to find out the instantaneous rate?

Answer 7

1. Draw a tangent to the curve.
2. Draw a right-angled triangle with the tangent (θ) as the hypotenuse.
3. Find the slope = tan θ = ΔV/Δ+.

(θ = hypotenuse, ΔV = vertical, Δ+ = horizontal)

Question 8

What are the three things needed for a reaction to take

place?

Answer 8

• Particles must collide if a reaction is to
  take place.
• They must collide with sufficient energy.
• They must collide effectively and
  frequently.

Question 9

What are the four factors that effect the rate of a reaction?

Answer 9

• Concentration
• Area
• Temperature
• Nature of reactants

Question 10

What is a catalyst poison?

Answer 10

It is a substance which makes a catalyst inactive.

Question 11

What is the nature of covalent compounds?

Answer 11

They hold slow reactions and bonds are broken before new ones are formed.

Question 12

What is the nature of ionic compounds?

Answer 12

They hold fast reactions and oppositely charged

ions come together.

Question 13

Name an example of a catalyst and how it works.

Answer 13

Hydrogen peroxide decomposes into water and oxygen at room temperature, the addition of magnesium di-oxide to the hydrogen peroxide causes it to decompose faster.

or

2H2O2 —> 2H2O + O2

Question 14

What are two biological catalysts and how do they work?

Answer 14

Catalase - breaks down H2O2.

• Amylase - breaks down starch to maltose.

Question 15

What are the three types of catalysts?

Answer 15

• Homogenous
• Heterogenous
• Autocatalysis

Question 16

What are the main features of a monogenous catalyst?

Name an example.

Answer 16

• Both reactants and catalysts are in the same phase (same physical state).
• There is no boundary between the reactants and catalyst.

Example: Potassium iodide breaks down hydrogen peroxide into water and oxygen.
(2H202 —> 2H20 + O2)

Question 17

What are the main features of a heterogenous catalyst?

Name an example.

Answer 17

• Reactants and catalyst are in different states.
• There is a boundary between the reactants and catalyst

Example: Hydrogen peroxide (L) and manganese di-oxide (S).
(2H202 —> 2H20 + O2)

Question 18

What is autocatalysis?

Answer 18

• It is when one of the products of a reaction catalysis the reaction.

Question 19

What is the general formula for the intermediate Formation Theory - Homogeneous
Catalysis Mechanism?

Answer 19

General Formula:

W + X —> Y + Z

Question 20

Name and explain the three stages of the Surface Adsorption Theory - Heterogeneous
Catalysis Mechanism.

Answer 20

• Adsorption - reactants attach to the bonds to the surface of the catalyst.
• Reaction - reactants react to form products.
• Desorption - products leave the surface of the catalyst.

Question 21

What does a catalytic converter do?

Answer 21

It converts environmentally harmful gases into harmless gases.

Question 22

What are the four chemicals that car exhausts can release without having a catalytic converter?

Answer 22

• Carbon monoxide
• Nitrogen monoxide
• Nitrogen dioxide
• Unburned hydrocarbons

Question 23

How are catalytic converters designed?

Answer 23

A thin coating of platinum is placed on a metal honeycomb structure inside a stainless steel case. The catalysts are spread over the surface of the honeycomb, which has a large surface area.

Question 24

What is the theory of collision?

Answer 24

For a reaction to occur, the particles must collide, they must collide with the appropriate orientation, and they must collide with sufficient energy. An effective collision is one that results in the formation of products