3.1.5 kinetics (only things didnt know)

Question 1

collision theory

Answer 1

for a reaction to take place , particles must collide with enough energy (activation energy) and correct orientation to react

Question 2

to get lots of collisions

Answer 2

you need a lot of particles per unit volume. For the particles to have enough energy to break bonds they need to be moving fast so for a fast rxn you need plenty of fast moving particles in a small space

Question 3

liquids & gases

Answer 3

particles in liquids and gases are always moving and colliding with each other however, most collisions don’t result in a reaction due to the wrong conditions e.g. wrong orientation or not enough energy.

Question 4

activation energy

Answer 4

the minimum amount of kinetic energy that particles need to react

Question 5

exothermic reaction

Answer 5

• energy of the reactants is higher than the energy of the products
• theres a negative energy change
• exothermic reactions release heat energy
• the energy released when forming new bonds is higher than the energy needed to break bonds

Question 6

look at rxn profile online for exothermic rxn slide 4

Question 7

endothermic rxn

Answer 7

• energy of the products is higher than the energy of the reactants
• there is a positive energy change
• endothermic reactions require the input of heat energy
• the energy needed to break bonds is higher than the energy released forming new bonds

Question 8

look at rxn profile for endothermic slide 5

Question 9

look at maxwell boltzmann distribution graph

Question 10

factors affecting rate of rxn : temp

Answer 10

• increasing temp increases rate of rxn
• more particles / a grater proportion of particles have energy greater than activation energy
• increases the speed of the molecules as greater kinetic energy
• resulting in more frequent successful collisions
• changes the maxwell boltzmann curve

Question 11

factors affecting rate of rxn : surface area

Answer 11

• increasing the surface area increases the rate of rxn
• increasing the amount of the particles exposed to the rxn
• there’s more particles available to collide
  -‘resulting in more frequent successful collision
• doesn’t change the maxwell boltzmann curve as has no effect on the energy of particles

Question 12

factors affecting rate of rxn : catalyst

Answer 12

• using a catalyst increases the rate of rxn
• they provide an alternative pathway for the rxn that has a lower activation energy
• they don’t get used up
• changed the maxwell boltzmann curve

Question 13

factors affecting rate of rxn : conc of solution / pressure of gas

Answer 13

• increasing conc of sol or pressure of gas increases rate of rxn
• there’s more particles per unit volume
• resulting in more frequent successful collisions
• as rxn proceeds reactants are being used up so their conc falls so the rate of rxn slows as the rxn progresses
• doesn’t change the maxwell boltzmann curve as has no effect on the energy of particles

Question 14

effect of temp on rate : higher temp

Answer 14

• at higher temps the peak of the curve (most probable energy) is lower and moves to the right along with the average
• bc more particles also have energy greater than the activation energy so there is more frequent successful collisions

Question 15

effect of temp on rate : small increase in temp

Answer 15

• can lead to a large increase in number of particles with energy greater than activation energy which leads to a faster rate of rxn

Question 16

catalysts

Answer 16

catalysts are substances that speed up the rate of a chemical rxn by providing an alternative pathway for the reaction with a lower activation energy however, they’re not used up or chemically changed at the end of a rxn

Question 17

why are they useful in industry

Answer 17

• cheaper to use catalyst than it is to increase the temperature or pressure
• can also be reused so even though the initial cost may be high you can use the catalyst again

Question 18

effect of catalysts on rate

Answer 18

• moved the activation to the left
• means the activation energy is lower + therefore more particles have activation energy + therefore reaction rate is increased

Question 19

catalyst example

Answer 19

haber process where an iron catalyst is used to