Rates of Reactions

Question 1

What is the Rate of a Reaction

Answer 1

The rate of reaction is the change in concentration per unit time of any one reactant or product

Question 2

What are factors affecting rate of reaction?

Answer 2

Nature of reactants, particle size, concentration, temperature, catalysts

Question 3

How do you draw rate graphs?

Answer 3

Concentration v. (1/Time) or Temp v. (1/Time)
(1/Time) used as Rate and Time inversely related (shorter time means faster rate)
Be careful with units of 1/time

Question 4

Catalyst

Answer 4

is a substance that alters the rate of reaction but is not consumed in the reaction

Question 5

Homogeneous catalysis

Answer 5

Homogeneous catalysis occurs when the reactants and the catalyst are in the same phase. example =?

Question 6

Heterogeneous catalysis

Answer 6

Heterogeneous catalysis occurs when the reactants and the catalyst are in different phases

Question 7

Autocatalysis

Answer 7

Occurs when on of the products of the reaction catalyses the reaction. e.g. Mn2+ ions in KMnO4 titrations (purple changes to colourless more quickly as titration proceeds

Question 8

Mechanisms of Catalysis

Answer 8

Intermediate Formation theory

Surface Adsorption theory

Question 9

Collision Theory

Answer 9

For a reaction to occur the reacting particles must collide with each other. A collision only results in a product being formed if a certain minimum energy is exceeded (called activation energy)

Question 10

Activation Energy

Answer 10

The minimum energy which colliding particles must have for a reaction to occur

Question 11

How to calculate instantaneous rate?

Answer 11

1. Draw a tangent to the curve
2. Draw a right angle with the tangent as the hypotenuse.
3. Slope = tan Theta = DeltaV over Delta T

Question 12

Draw how to calculate instantaneous rate and explain each part.

Answer 12

.

Question 13

What conditions need to be in place for a reaction to occur?

Answer 13

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

Question 14

Factors that effect the rate of a reaction

Answer 14

Concentration, Catalyst, Area, Temperature and Nature of reactants.

Question 15

What are the nature of reactants of covalent compounds?

Answer 15

Slow Reactions

Bonds are broken before new ones are formed

Question 16

What are the nature of reactants of Ionic compounds?

Answer 16

Fast Reactions

Oppositely charged ions come together

Question 17

How does temperature affect rates of reaction?

Answer 17

Hotter the temperature - the more energy the particles have - the faster the particles move. Therefore, more effective and frequent collisions and the reaction occurs quicker. Therefore, the higher the temperature, the shorter the reaction time.

Question 18

At lower temperatures, the reaction time is ______.

Answer 18

longer

Question 19

At higher temperatures, the reaction time is _______.

Answer 19

shorter

Question 20

Does increasing concentration decrease or increase the rate of a reaction?

Answer 20

Increasing concentration, increases the rate of a reaction.

Question 21

At lower concentration the reaction time is _____.

Answer 21

longer

Question 22

At high concentrations the reaction time is _______.

Answer 22

shorter

Question 23

What is a catalyst?

Answer 23

A catalyst is a substance that alters the rate of a chemical reaction but is not consumed in the reaction.

Question 24

What does hydrogen peroxide decompose into at room temperature and what happens if you add manganese dioxide?

Answer 24

Hydrogen peroxide decomposes into water and oxygen at room temperature, the addition of manganese dioxide as a catalyst causes hydrogen peroxide to decompose faster.

Question 25

What are the properties of catalysts?

Answer 25

Remain chemically unchanged at end of reaction.
Specific - work for one reaction but not another.
Only needed in small amounts.
In equilibrium reactions, a catalyst helps equilibrium to be achieved quicker.

Question 26

What are the 3 types of catalysis?

Answer 26

1. Homogenous 2. Heterogeneous 3. Autocatalysis

Question 27

What is homogenous catalysis?

Answer 27

Both reactants and catalyst are in the same phase (same physical state). There is not boundary between the reactants and the catalyst.

Question 28

Give an example of homogenous catalysis.

Answer 28

E.g. Both reactants and catalyst are liquids - aqueous potassium iodide and hydrogen peroxide, potassium iodide breaks H2O2 into water and oxygen

Question 29

What is heterogeneous catalysis?

Answer 29

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

Question 30

Give an example of heterogeneous catalysis.

Answer 30

E.g. Hydrogen peroxide (liquid) and manganese dioxide (solid) or oxidation of methanol by platinum catalyst.

Question 31

What is autocatalyis?

Answer 31

Autocatalysis is where one of the products of a reaction catalyses the reaction.

Question 32

Give an example of autocatalysis.

Answer 32

E.g. Reduction of Manganate (VII)
MnO4- + 8H+ + 5Fe2+ -> Mn2+ + 5Fe3+ + 4H2O
-Mn2+ catalyses the reaction
-Purple colour decolorises slowly
-Then decolorising speeds up due to Mn2+ ions produced, catalysing the reaction.

Question 33

What is chemical equilibrium?

Answer 33

Chemical Equilibrium is a state of dynamic balance where the rate of the forward reaction equals the rate of the reverse reaction.