KINETICS

Question 1

Describe what must happen before a reaction will take place

Answer 1

• particles must collide with sufficient energy to break bonds (so need to be moving fast)

Question 2

describe a chemical reaction in terms of collision theory

Answer 2

-reactions occur when reactant particles collide with sufficient energy called activation energy

Question 3

Define activation energy

Answer 3

minimum amount of energy needed for a reaction to occur and a collision to be successful

Question 4

Explain why most collisions between particles do not result in a chemical reaction

Answer 4

the energy of reactant particles is distributed with very few, having
E≥Ea

Question 5

Explain how temperature affects the number of molecules with energy equal to or more than the activation energy

Answer 5

at higher temperature, more particles have E≥Ea so more successful collisions per unit time that results in a reaction

Question 6

Explain why a small increase in temperature has a large effect on ROR

Answer 6

-At higher temp significantly more particles have E≥Ea
-so more collisions are successful

Question 7

Explain the effect that lowering temp of a chemical reaction changes the rate at which a chemical reaction occurs

Answer 7

-at lower temp the average energy of particles decrease
-less particles have E≥Ea
-there are less collisions per unit time

Question 8

Define ROR

Answer 8

change in the amount of reactant or product per unit time

Question 9

Explain why Maxwell-Boltzman graph starts at the origin

Answer 9

no particles have 0 kinetic energy

Question 10

What does the area under Maxwell-Boltzman graph show

Answer 10

total number of particles

Question 11

What Maxwell-Boltzman graph tells us

Answer 11

• no particles have 0 energy
  -most particles have intermediate energies - around peak of curve (most probable energy of particles)
  -few have very high energies (right hand side of curve)
  -average energy isn’t the same as the most probable energy (different places as they’re not symmetrical)

Question 12

Explain how the reaction between HCL and sodium thiosulfate can be monitored

Answer 12

-reactions produces a sulfur participate
-time how long it takes for the ppt to obscure the cross
-rate = 1/time

Question 13

Explain the reaction between HCL and sodium thiosulfate should only be carried out on a small scale

Answer 13

product = toxic sulfur dioxide

Question 14

Explain how increasing conc affects the rate of a chemical reaction

Answer 14

-as conc increases there are more reactant particles per unit volume
because more particles have E≥Ea
-more successful collisions per unit time

Question 15

Explain how increasing pressure affects the rate of a chem reaction

Answer 15

-as pressure increases there are more reactant particles per unit volume because more particles have E≥Ea
-more successful collisions per unit time

Question 16

Define catalyst

Answer 16

substance that increases the rate of a chemical reaction without being used up or permanently changed itself

Question 17

Explain how a catalyst works

Answer 17

-provides an alternative reaction pathway with a lower activation energy
-more particles have E≥Ea

Question 18

Explain the shape of the graph showing the conc of a reaction over time

Answer 18

-initial rate is fast (steep gradient) as there is max no. of particles, hence successful collisions
-rate slows (gradient decreases) as particles get used up and successful collisions decrease
-gradient becomes 0 when reactant particle have been used up