kinetics

Question 1

what is kinetics

Answer 1

Kinetics is the study of the factors that affect the rates of reaction

Question 2

what is rates of reaction

Answer 2

the rate of reaction is how quickly the reaction takes place

Question 3

are all rates of reactions the same

Answer 3

There is a large variation in reaction rates
e.g. popping a test tube full of hydrogen is over in a fraction of a second

complete rusting of an iron nail could take several years

Question 4

how can you change the speed of a reaction

Answer 4

reactions can be sped up or slowed down by changing the conditions of the reaction

Question 5

what must happen for a reaction to take place

Answer 5

for a reaction to take place between two particles they must collide with enough energy to break bonds

Question 6

where must the collision take place

Answer 6

The collision must take place between the parts of the molecule that is going to react together.

Therefore orientation has a part to play

Question 7

How do you get a lot of collisions

Answer 7

you need a lot of particles in a small volume

Question 8

how do particles get enough energy to break bonds

Answer 8

for the particles to have enough energy to break bonds, they need to be moving fast.

Question 9

how can we have a fast reaction rate

Answer 9

A fast reaction rate requires rapidly moving particles and a small volume

Question 10

do all collisions between particles lead to a reaction

Answer 10

most reactions btween molecules or oher particles do not lead to a reaction because:

they do not have enough energy ( to break the bonds )

they are in the wrong orientation

Question 11

what effects the rates of chemical reactions

Answer 11

increasing the temperature

increasing the concentration of a solution

increasing the pressure of gas reaction

increasing the surface area of solid reactants

using a catalyst

Question 12

how does increasing the temperature affect the rate of chemical reaction

Answer 12

increases the speed of the molecules which in turn increases their energy and the number of collisions

Question 13

how does increasing the concentration of a solution affects the rate of chemical reaction

Answer 13

more particles present in a given volume then more collisions are more likely to happen and the reaction would be faster

Question 14

how does increasing the pressure of a gas reaction effect the reaction

Answer 14

same effect as increasing concentration of a solution

more molecules or atoms in a given volume so more collisions are likely therefore speeding the reaction up

Question 15

how does increasing the surface area of a solid reactant effect the rate of reaction

Answer 15

the greater the surface area of the solid, the more of its particles are available to collide with molecules in a gas or liquid. This means that breaking a solid lump into smaller pieces increases the rate of its reactions because there are more sites for reaction

Question 16

what is a catalyst and how does it effect the rate of reaction

Answer 16

a catalyst is a substance that can change the rate of a chemical reaction without being chemically changed itself

Question 17

what must happen for a collision to result in a reaction

Answer 17

the molecules must have a certain minimum energy, enough to start breaking bonds. This energy is called the activation energy

Question 18

what is an exothermic reaction

Answer 18

exothermic reactions transfer energy from molecules to the surroundings. This causes the surroundings to heat up

Question 19

what are some examples of exothermic reactions

Answer 19

1. combustion

2. certain oxidation and neutralization reactions

Question 20

how does a reaction profile/ enthapy diagram look like for a exothermic reaction

Answer 20

Products have less energy than the reactants. This is because energy is being transferred from reaction to the surroundings

The difference between the reactants and the energy in the products tells us the energy that is being released to the surroundings

Question 21

what are some uses for exothermic reactions

Answer 21

1. hand warmers

2. self heating cans e.g. for food and drinks

Question 22

what is an endothermic reaction

Answer 22

endothermic reactions take in energy from their surroundings therefore, the temperature of the surroundings get decrease [ get colder].

Question 23

what are some examples of endothermic reactions

Answer 23

thermal decomposition

Question 24

how does an energy profile/ enthapy look like for a endothermic reaction

Answer 24

Products have more energy energy than reactants because energy is being taken in from the surroundings

The difference in energy between the reactants and products tells is the amount of energy taken in by the reaction

Question 25

what do both of the reaction profiles of endothermic and exothermic reactions have in common

Answer 25

Both endo and exo energy profiles both have something in common - the energy rise to a peak. This is the activation energy. The activation energy is from the reactants to the peak

Question 26

what happens if the reaction has a large activation energy

Answer 26

This reaction will take place extremely slowly at room temperature because very few collisions will have sufficient energy to bring about a reaction ( break bonds)

Question 27

what happens if a reaction has a small activation energy

Answer 27

This reaction will take place rapidly at room temperature because many collisions will have enough energy to bring about a reaction (break bonds)

Question 28

what is the species

Answer 28

species is a term tat used by chemists to refer to an atom, molecule or ion.

Question 29

what is the species that exists at the top of an enthapy/ energy profile

Answer 29

The species that is at the top of the curve of an enthapy diagram is called a transition state or activated complex. Some bonds are in the process of being made and some are in the process of being broken.

It has extra energy and is unstable

Question 30

what is the Maxwell- Boltzmann distribution

Answer 30

Particles in any gas ( or solution) are all at different speed e.g.

• few are moving slowly
• few are very fast
• most are in the middle

Energy of a particles depends on its speeds the particles also have are range of energies.
If you plot a graph of energy against the fraction of particles that have energy, you end up with a curve.

This shape us called the Maxwell- Boltzmann distribution - it tells us the distribution of energy amongst particles

Question 31

describe the shape of the graph

Answer 31

• The area under the graph represents the total number of particles
• no particles have zero energy hence why the graph always starts at 0-0
• most particles have intermediate energies ( around the peak of the curve)
• a few have very high energies ( the right hand side of the curve) . In fact there is no upper limit
• the most probable energy is at the peak. It is the energy with the most particles
• the average energy is slightly to the left of the probable energy. The average energy is not the same as the probable energy

Question 32

what is the activation energy and where is it marked on the Maxwell Boltzmann distribution graph

Answer 32

in order for a reaction to take place, collisions between particles must have enough energy to start breaking bonds. This amount of energy is called the activation energy

If you mark Ea on a Maxwell Boltzmann distribution graph the area underneath the graph to the right of the Ea represents the number of particles with enough energy to react

Question 33

how does temperature affect the shape of the M.B graph

Answer 33

the higher the temperature:

• the peak of the curve is lower and moves to the right
• the number of particles with very high energy increases
• the graph shows that at a higher temperature more molecules have enough energy greater or the same as the Ea. This means a higher percentage of collisions will result in a reaction

Question 34

why does the reaction rate increases with temp

Answer 34

a small increase in temperature produces a large increase in the number of particles with energy greater than or the same as the activation energy (Ea)

Question 35

what are catalysts

Answer 35

catalysts are substances that affect the rate of chemical reactions without being chemically changed themselves at the end of the reaction

Question 36

why are catalysts important in the industry

Answer 36

catalysts are used to speed up reactions so they are important in the industry

It is cheaper to speed up a reaction by using a catalyst than by using high temperatures and pressures. This is even if the catalysts are expensive as they are not used during the reaction.

Question 37

how do catalyst work

Answer 37

catalyst provides a different pathway for the reaction, one with lower activation energy.
Therefore, they reduce the activation energy ( the minimum amount of energy that is needed to start the reaction)

Question 38

how can we show the affect of the catalyst on a Maxwell Boltzwell distribution graph

Answer 38

the activation energy marked Ea on the graph will move to the left as the activation energy is lower

Question 39

what is a catalytic converter

Answer 39

all new petrol cars are now equipped with a catalytic converter in their exhaust systems. This reduces the levels of a number of polluting gases.

catalytic converters are in the shape of a honeycomb. It is made of a ceramic material coated with platinum and rhodium ( the catalysts)
The honeycomb shape provides an enormous surface area, on which the reaction takes place - a little goes a long way

Question 40

how do catalytic converters work

Answer 40

as the polluting gases pass over the catalysts, they react with each other to form less harmful products by the following reactions:

carbon monoxide + nitrogen oxides = nitrogen + carbon dioxide

hydrocarbons + nitrogen oxides = nitrogen + carbon dioxide + water