Reactions

Front 1

Name an example of a slow reaction.

Back 1

The rusting of iron

Front 2

Name an example of a moderate speed reaction

Back 2

A metal (like magnesium) reacting with acid to produce a gentle stream of bubbles.

Front 3

Name an example of a 'really fast' reaction.

Back 3

An explosion, where it's over in a fraction of a second.

Front 4

Name the four things that the rate of reaction depends upon.

Back 4

1) Temperature

2) Concentration (or pressure, for gases).

3) Catalyst

4) Surface area (or size of solid pieces).

Front 5

How can the rate of a reaction be observed?

Back 5

1) By measuring how quickly the reactants are used up

2) By measuring how quickly the products are formed

Front 6

Name three things we can use to measure the rate of a reaction.

Back 6

1) Precipitation

2) Change in mass (usually has given off)

3) The volume of gas given off

Front 7

What is precipitation?

Back 7

When the product of the reaction is a precipitate which clouds the solution.

Front 8

How can we use precipitation to measure the rate of reaction?

Back 8

1) Observe a mark through the solution and measure how long it takes to disappear.

2) The quicker the mark disappears, the faster the reaction.

3) This only works for reactions where the initial solution is see-through.

4) The result is very subjective - different people might not agree over the exact point when the mark 'disappear'.

Front 9

How can we use a change in mass to measure the rate of reaction?

Back 9

1) It can be carried out on a mass balance

2) As the gas is released, the mass disappearing is easily measured on the balanced

3) The quicker the reading on the balance drops, the faster the reaction

This is the most accurate of the three methods described because the mass balance is very accurate. It does have the disadvantage of releasing as straight into the room.

Front 10

How can we use the volume of gas given off to measure the rate of reaction?

Back 10

1) Involves the use of a gas syringe to measure the volume of gas given off

2) The more gas given off during a given time interval, the faster the reaction

3) They're normally quite accurate - they measure accurately to the nearest millilitre.

Front 11

State what the collision theory is.

Back 11

It says that the rate of reaction depends on how often and how hard the reacting particles collide with each other.

Front 12

Describe the reaction of HCL and marble chips.

Back 12

Used to demonstrate the effect of breaking the solid up into small bits. Shows how surface area affects the rate of reaction.

1) the HCL and marble chips react and produce carbon dioxide gas.

2) repeat the experiment many times, each time, decrease the size of the marble chips (but keep the mass the same).

Front 13

Describe the reaction of magnesium with dilute HCL

Back 13

Used to measure the effects of increased concentration on the rate of a reaction.

1) magnesium and HCL react and give off hydrogen gas.

2) the more gas produced in a specific amount of time, the more vigorous the reaction

3) repeat the reaction several times, changing the concentration of the acid and record the results

Front 14

Describe the reaction of sodium thiosulphate and HCL.

Back 14

Used to demonstrate the effects of temperature on the rate of reaction.

1) both solutions are clear

2) they react together to form a yellow precipitate

3) the experiment involves watching a black mark disappear through the cloudy sulphur and timing how long it takes to go.

4) as the temperature increases, the rate of reaction increases, so the precipitate forms faster, meaning the mark disappears faster

Front 15

Complete the sentence:

More collisions between particles of reactants increase...

Back 15

...the rate of reaction

Front 16

In terms of the collision theory, how does a larger surface area affects the rate of reaction?

Back 16

Breaking up a solid into smaller pieces increases the total surface area. This means the particles around it in the solution will have more area to work on, so there'll be more frequent collisions.

Front 17

In terms of the collision theory, how does a higher concentration of reactant affect the rate of reaction?

Back 17

If a solution is more concentrated, it means there are more particles of reactant, which makes collisions between them more likely.

In a gas, increasing the pressure squishes the particles closer together so there will be more frequent collisions.

Front 18

In terms of the collision theory, how does a higher temperature affect the rate of reaction?

Back 18

When the temperature is increased, the particles have more energy, meaning they move faster, which means that they collide more often.

Front 19

Complete the sentence:

Reactions only happen if...

Back 19

...the particles collide with enough energy.

Front 20

What is the minimum amount of energy needed by the particles to react known as?

Back 20

The 'activation energy'.

Front 21

Complete the sentence:

At a higher temperature, there will be more particles colliding with enough energy...

Back 21

...to make the reaction happen.

Front 22

What is a catalyst?

Back 22

A substance that speeds up a reaction without being changed or used up in the reaction.

Front 23

What are the advantages of using catalysts in industry?

Back 23

Advantages:
- They increase the rate of reaction, which saves money because the plant doesn't need to operate for as long to produce the same amount of the product.

- The catalyst allows the reaction to happen at a much lower temperature, reducing the energy needed (and so reducing the energy cost).

- They don't get used up, so you are able to reuse them.

Front 24

What are the disadvantages of using catalysts in industry?

Back 24

Disadvantages:

- They can be expensive to buy and often need to be removed from the product and cleaned.

- Different reactions require different catalysts, so if you make more than one product at the factory, you'll need to buy a different catalyst for each of them.

- Catalysts can be 'poisoned' by impurities, so they stop working.

Front 25

Complete the sentence:

Whenever chemical reactions occur...

Back 25

...energy is transferred to or from the surroundings.

Front 26

What is an exothermic reaction?

Back 26

A reaction which transfers energy to the surroundings, usually in the form of heat and usually shown by a rise in temperature.

Front 27

Give an example of an exothermic reaction.

Back 27

1) The burning of fossil fuels (combustion).

2) Neutralisation reactions (acid + alkali).

3) Many oxidation reactions.

Front 28

Give an example of an everyday use of an exothermic reaction.

Back 28

1) Hand warmers use the exothermic oxidation of iron in air (with a salt solution catalyst) to generate heat.

2) Self-heating cans of drinks rely on exothermic reactions between chemicals in their bases.

Front 29

What is an endothermic reaction?

Back 29

A reaction which takes in energy from the surroundings, usually in the form of heat and is usually shown by a fall in temperature.

Front 30

Are endothermic reactions more or less common than exothermic reactions?

Back 30

Endothermic reactions are less common than exothermic reactions.

Front 31

Give an example of an endothermic reaction.

Back 31

Thermal decomposition. Heat must be supplied to make calcium carbonate decompose to make quicklime.

Front 32

Give an everyday use of an endothermic reaction.

Back 32

Sports injury packs. They take in heat and the pack becomes very cold. They are more convenient than carrying ice around!

Front 33

Fill the blanks:

In __________ reactions, if the reaction is ___________ in one direction, it will be exothermic in the other direction. The ______ absorbed by the ___________ reaction is equal to the energy released during the __________ reaction.

Back 33

In reversible reactions, if the reaction is endothermic in one direction, it will be exothermic in the other direction. The energy absorbed by the endothermic reaction is equal to the energy released during the exothermic reaction.