Rates of Reaction

Question 1

Rate of Reaction

Answer 1

the change in concentration per unit of time of any one product or reactant

Question 2

Instantaneous rate of reaction

Answer 2

the rate of reaction at any one particular time during a reaction

Question 3

average rate of reaction

Answer 3

total gas produced over total time

Question 4

Factors Affecting RoR

Answer 4

-nature of reacants
-particle size
-concentration
-temperature
-catalyst

Question 5

Nature of Reactants

Answer 5

-ionic reactions are fast because ions are free to move in solution.. no bonds break (sodium chloride and silver nitrarte–> a percipitate of silver chloride forms instantly)
-covalent reactions are slower than ionic as covelent bonds need to be broken before the reaction can occur (hcl and sodium thiosulfate–> pale yellow percipitate of sulphur forms slowly)

Question 6

Particle Size

Answer 6

the rate of reaction increases as the particle size decreases becasue the smaller the particle size, the large the surface area therefore the greater number of collisions, the greater number of successful collisions
( eg. Marble Chips)

Question 7

Concentration

Answer 7

the greater the concentration, the greater the rate of reaction (directly proportional). if the concentration is increaded the number of collisions is also increased
(eg sodium thiosulfate and hydrochloric acid)

Question 8

Temerapture

Answer 8

the greater the temberature the greater the rate (exponential relationship) because as the temperature increases, the more if the colliding molecules have the minimum activation energy needed to react.
(eg sodium thiosulfate and hcl)

Question 9

Catalyst

Answer 9

a substance that alters the rate of a chemical reaction but is not used up/consumed in the reaction itself. a catalyst reduces the amount of energy needed for an effective collision
(MnO2 is a catalyst in the breaking down of H2O2 to water and oxygen)

Question 10

Properties of Catalysts

Answer 10

1. specific - each catalyst only acts on one type of reaction (eg enzymes, a bio catalyst made by living cells how this as as the enzyme catalase only breaks down hydrogen peroxide)
2. only needed in small amounts
3. catalyst alters both the forward rate and the reverse rate by the same amount if the reaction is reversable
4. can be poisoned by certain substances

Question 11

Types of Catalyst

Answer 11

1. Homogeneous catalyst: the same phase as the reactants
2. Heterogeneous catalysts: in a different phase to the reactants
3. Autocatalysis: a product of the reaction that acts as a catalyst

Question 12

Mechanism of Catalysts

Answer 12

the decomposition of hydrogen peroxide catalysed by the resence of I ions illustrated the formation of an intermediate
1. H2O2 + I- –> H2O +IO-
2. H2O2 +IO- –>H2O + O2 + I-

Question 13

Surface Adsorption Theory

Answer 13

1. reactants are adsorbed onto the surbace of the catalyst, forming a temp bond
2. reactants are close together at high concentration on the surface and are therefore more likely to collide with each other and react
3. the products diffuse away from the surface of the catalyst

Question 14

Adsorption

Answer 14

moleculed adhere to the surface of the phase

Question 15

Absorption

Answer 15

moleecules are drawn into the buld of the phase

Question 16

Why are Transition Metals Excellent Catalysts?

Answer 16

have vacant d sublevels on which reactants come together, collide and react (eg. Iron, Platinum)

Question 17

Catalytic Converts

Answer 17

converts gases to enviornmentally friendly gases. they consist of a thin coating of platinum, palladium, and rhodium on a ceramic or metal honeyvomb inside a stainless steel case

Question 18

Collision Theory

Answer 18

• a particle must collidde before a reaction can take place
  -not all collision lead to a reaction
  -reactants mist possess at least a minimum amoint of engery

Question 19

Activation Energy

Answer 19

minimum combined energy of particles for effective collisions

Question 20

The Steric Effect

Answer 20

particels must approach each other in a certain way