Monitoring and Controlling Chemical Reactions

Question 1

how do you work out the rate of a reaction?

Answer 1

workout how fast the products are being formed or how fast the reactants are being used up

Question 2

does the rate of reaction stay the same throughout the whole reaction?

Answer 2

no, it starts faster and slows

Question 3

why does the rate of reaction decrease over time?

Answer 3

as more reactants are used up, less successful collisions take place.

Question 4

What is collision theory?

Answer 4

in order for particles to react, they have to collide with each other with sufficient energy.

Question 5

What is activation energy?

Answer 5

the energy required for particles to collide successfully and react

Question 6

What are 4 factors that effect rate of reaction?

Answer 6

temperature
conc/pressure
surface area
catalyst

Question 7

why does increased temperature increase the rate of reaction?

Answer 7

the particles have more energy so they collide successfully more often

Question 8

Why does increasing the concentration or pressure increase the rate of reaction?

Answer 8

there are more reactant particles in the same volume so the frequency of successful collisions increases

Question 9

Why does increasing the surface area increase the rate of reaction?

Answer 9

there are more particles exposed and therefore more particles are able to react, increasing the frequency of successful collisions

Question 10

What are catalysts?

Answer 10

substances that speed up a reaction without being used up

Question 11

How do catalysts increase rate of reaction?

Answer 11

they create an alternate pathway with less activation energy, meaning there are more successful collisions

Question 12

What are 3 examples of catalysts?

Answer 12

enzymes
cobalt
nickel

Question 13

Transition metals make good catalysts, true or false?

Answer 13

true

Question 14

What is the symbol for a reversible reaction?

Answer 14

⇌

Question 15

What is a reversible reaction?

Answer 15

one in which both the forward and backward reactions can take place.

Question 16

What are 3 important things about systems in equilibrium?

Answer 16

The forward and backward reactions occur at the same rate
The concentrations of the reactants and products remain constant
It requires a closed system

Question 17

At equilibrium, if the concentration of reactants is higher than the concentration of products, we say that the position of equilibrium lies to the:

Answer 17

left

Question 18

In a reversible reaction, if the forward reaction is exothermic, the backward reaction is _____.

Answer 18

endothermic

Question 19

If the position of equilibrium lies to the right, it means there are more:

Answer 19

products

Question 20

In a reversible reaction, if the forward reaction is endothermic, what would be the affect of increasing the temperature?

Answer 20

Equilibrium would shift to the right
Yield of products would increase

Question 21

In a reversible reaction, if the forward reaction is exothermic, what would be the effect of decreasing the temperature?

Answer 21

Yield of products would increase
Equilibrium would shift to the right

Question 22

If the concentration of reactants is more than the concentration of products, where does the equilibrium lie?

Answer 22

to the left

Question 23

What is le Chatelier’s principle?

Answer 23

the idea that if you change the conditions of a reversible reaction, the position of equilibrium will shift to try and counteract the change

Question 24

If the pressure is increased, where will the equilibrium shift to?

Answer 24

it will shift to the side with the least amount of molecules

Question 25

If you increase the concentration of a reactant, where will the equilibrium shift to?

Answer 25

the right

Question 26

In a reversible reaction, changes in pressure will only affect substances that are in the:

Answer 26

gaseous state

Question 27

H2(g) + I2(g) ⇋ 2HI(g)

In the above reaction, increasing the pressure will:

Answer 27

Have no effect on the position of equilibrium

Question 28

What is the formula for finding concentration from mass and volume?

Answer 28

conc. = mass/volume

Question 29

5.0 g of KNO3 is dissolved in 100 cm3 of water.
Calculate the concentration in g/dm3.

Answer 29

50

Question 30

How do you carry out a titration?

Answer 30

1) Use the pipette to add 25 cm3 of alkali to a clean conical flask.
2) Add a few drops of indicator and put the conical flask on a white tile.
3) Fill the burette with acid and note the starting volume.
4) Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix.
5) Stop adding the acid when the end-point is reached (this is when the acid has neutralised the alkali and the indicator changes colour).
Note the final volume reading, and calculate how much acid you added in total.
Repeat the titration until you get ‘concordant results’, which means volumes of acid that are within 0.10 cm3 of each other.
Use the concordant results to calculate the mean volume of acid required to neutralise the alkali.

Question 31

Why is it important to swirl the conical flask in titration?

Answer 31

as you add the acid from the burette in order to evenly distribute it, and ensure that the colour change occurs as soon as neutralisation takes place.

Question 32

Litmus is _____ in acidic solutions and _____ in alkaline solutions

Answer 32

red, blue

Question 33

Phenolphthalein is _____ in acidic solutions and _____ in alkaline solutions

Answer 33

colourless, pink

Question 34

Methyl orange in _____ in acidic solutions and _____ in alkaline solutions

Answer 34

red, yellow

Question 36

How do you work out the volume for a gas at room temperature and pressure using moles?

Answer 36

volume (dm^3) = moles * 24

Question 37

Calculate the volume of 6 g of helium (Ar = 4) at room temp. and pressure

Answer 37

moles = 6/4 = 1.5
1.5 * 24 =
36 dm^3

Question 38

What is the atom economy of a reaction?

Answer 38

A measure of the proportion of starting materials that end up as useful products

Question 39

2H2O2 → 2H2O + O2

Calculate the atom economy when forming oxygen from hydrogen peroxide. Give your answer to 3.s.f.

Answer 39

2H2O2 = 68
O2 = 32
32/68 * 100 = 47.1%

Question 40

What are the problems with low atom economy?

Answer 40

There will be more waste products which will have to be disposed of

It will be less sustainable as it will use more resources

Question 41

Identify 3 other factors, besides atom economy, that should be considered when choosing between two different methods of producing a useful product.

Answer 41

Percentage yield

Cost of raw materials

Position of equilibrium

Rate of reaction

Cost of maintaining the right conditions

Environmental impact of waste products

Question 42

What is the percentage yield of a reaction?

Answer 42

The actual yield of a reaction compared to the maximum theoretical yield

Question 43

Suggest 3 reasons why the percentage yield of a chemical reaction may be less than 100%.

Answer 43

The reactants may not all react (e.g. because the reaction is very slow or reaches equilibrium)

There may be side reactions, meaning that other products are produced instead

Some of the products may be lost (e.g. gases may float off, or some solids may be left on the filter paper)