chapter 6: reaction kinetics ⏱

Question 1

define activation energy

Answer 1

minimum energy which the colliding molecules must possess before a collision will result in a reaction

Question 2

define rate of reaction

Answer 2

the change in concentration of reactant or product with time

Question 3

define rate equation

Answer 3

experimentally determined equation that links the rate of reaction to the concentration of each reactants or catalyst to a specific power

Question 4

define order of reaction

Answer 4

power to which the concentration of that reactant/catalyst is raised in the experimentally determine rate equation

Question 5

define rate constant

Answer 5

proportionality constant in the rate equation

Question 6

define rate determining step

Answer 6

slowest step in a reaction mechanism

Question 7

define catalyst

Answer 7

substance which increases the rate of reaction by providing a different reaction pathway with a lower activation energy without itself going through any permanent chemical change

Question 8

how to find instantaneous rate

Answer 8

gradient of tangent at time t

Question 9

how to find initial rate

Answer 9

gradient of tangent at T=0

Question 10

define half life

Answer 10

time taken for the concentration of a reactant to reduce to half of its initial value

Question 11

what are the factors that affect the value of rate constant

Answer 11

1. temperature
2. addition of catalyst

Question 12

why does an increase in concentration increase rate of reaction

Answer 12

when concentration of reactant increases,
- number of particles per unit volume increase
- increase frequency of effective collision
- acc. to collision theory, rate of reaction increases

Question 13

why does an increase in temperature increase the rate of reaction

Answer 13

when temp. increases
- avg. KE of reactant molecules increase
- more molecules have higher energy
- more collision with energy greater than or equal to Ea
- frequency of effective collision increase
- rate of reaction increase

Question 14

how does addition of a catalyst increase rate of reaction

Answer 14

• catalyst provides an alternative pathway with lower Ea
• more molecules have energy greater than or equal to lowered Ea
• frequency of effective collision increases
• rate of reaction increases

Question 15

define heterogenous catalysis

Answer 15

exists in a different phase from reactants and increases rate of reaction by providing a different reaction pathway with a lower activation energy without itself undergoing permanent chemical change

Question 16

explain the mode of action of heterogenous catalyst (first step)

Answer 16

reactant molecules are adsorbed on the active site of the catalyst via weak temporary bonds

Question 17

explain the mode of action of heterogenous catalyst (second step)

Answer 17

reactant molecules are brought closer together, increasing their concentration at the catalyst surface

Question 18

explain the mode of action of heterogenous catalyst (third step)

Answer 18

bonds in reactant molecules are weakened, lower Ea

Question 19

explain the mode of action of heterogenous catalyst (fourth step)

Answer 19

molecules are orientated in the right position for reaction, increasing number of effective collisions

Question 20

explain the mode of action of heterogenous catalyst (last step)

Answer 20

product is deserved from the catalyst surface, regenerating active site on the catalyst

Question 21

define homogeneous catalysis

Answer 21

exists in the same phase from reactants and increases the rate of reaction by providing a different reaction pathway with a lower activation energy without itself undergoing any permanent change

Question 22

why do the reaction of I- and S2O8 2- have high Ea

Answer 22

both reactants are negatively charged and they tend to repel each other

Question 23

what does NO2 do

Answer 23

presence of small amounts of NO2 in the atmosphere can catalyse the oxidation of SO2 to SO3 by providing an alternative mechanism of lower Ea

Question 24

when does autocatalysis occur

Answer 24

when product catalyses the reaction