C7.2 - Using energy transfers from reactions

Question 1

What can chemical hand and body warmers be?

Answer 1

Chemical:
1. Hand
2. Body
warmers can be very useful

Question 2

Chemical hand and body warmers can be very useful.

What do these products use to warm you up?

Answer 2

These products use exothermic reactions to warm you up

Question 3

What can people do with hand warmers?

Answer 3

People can take hand warmers to places they know will get very cold

Question 4

People can take hand warmers to places they know will get very cold.
Example

Answer 4

For example, spectators at outdoor sporting events in winter can warm their hands

Question 5

What do people usually use chemical body warmers to do?

Answer 5

People usually use chemical body warmers to help ease:

1. Aches
2. Pains

Question 6

What can some hand warmers be?

Answer 6

Some hand warmers can only be used once

Question 7

Some hand warmers can only be used once.

What do these hand warmers make use of?

Answer 7

These hand warmers make use of the energy transferred to the surroundings in the oxidation of iron

Question 8

Some hand warmers can only be used once.
These hand warmers make use of the energy transferred to the surroundings in the oxidation of iron.
What happens to iron, in an exothermic reaction?

Answer 8

In an exothermic reaction, iron turns into hydrated iron(III) oxide

Question 9

Some hand warmers can only be used once.
These hand warmers make use of the energy transferred to the surroundings in the oxidation of iron.
Iron turns into hydrated iron(III) oxide in an exothermic reaction.
What is the reaction similar to?

Answer 9

The reaction is similar to rusting

Question 10

Some hand warmers can only be used once.
These hand warmers make use of the energy transferred to the surroundings in the oxidation of iron.
Iron turns into hydrated iron(III) oxide in an exothermic reaction.
What is used as a catalyst?

Answer 10

Sodium chloride (common salt) is used as a catalyst

Question 11

Some hand warmers can only be used once.
These hand warmers make use of the energy transferred to the surroundings in the oxidation of iron.
Sodium chloride (common salt) is used as a catalyst.
What is this type of hand warmer?

Answer 11

This type of hand warmer is disposable

Question 12

Some hand warmers can only be used once.

What can other hand warmers be?

Answer 12

Other hand warmers can be used many times

Question 13

Some hand warmers can only be used once.
Other hand warmers can be used many times.
What are these based on?

Answer 13

These hand warmers are based on the formation of crystals from solutions of a salt

Question 14

Some hand warmers can only be used once.
Other hand warmers can be used many times.
These hand warmers are based on the formation of crystals from solutions of a salt.
What is the salt used often?

Answer 14

The salt used is often sodium ethanoate

Question 15

Some hand warmers can be used many times.
These hand warmers are based on the formation of crystals from solutions of a salt.
The salt used is often sodium ethanoate.
A supersaturated solution is prepared by doing what?

Answer 15

A supersaturated solution is prepared by dissolving as much of the salt as possible in hot water

Question 16

Some hand warmers can be used many times.
These hand warmers are based on the formation of crystals from solutions of a salt.
What is used to start the exothermic change?

Answer 16

A small metal disk in the plastic pack is used to start the exothermic change

Question 17

Some hand warmers can be used many times.
These hand warmers are based on the formation of crystals from solutions of a salt.
A small metal disk in the plastic pack is used to start the exothermic change.
What happens when you press the small metal disk?

Answer 17

When you press the small metal disk a few times, small particles of metal are scraped off

Question 18

Some hand warmers can be used many times.
These hand warmers are based on the formation of crystals from solutions of a salt.
A small metal disk in the plastic pack is used to start the exothermic change.
When you press the small metal disk a few times, small particles of metal are scraped off.
These ‘seed’ (or start off) the crystallisation.
What do the crystals do?

Answer 18

The crystals spread throughout the solution, transferring energy to the surroundings in an exothermic change

Question 19

Some hand warmers can be used many times.
These hand warmers are based on the formation of crystals from solutions of a salt.
How do you reuse the warmer?

Answer 19

To reuse the warmer, you simply put the solid pack into boiling water to re-dissolve the crystals

Question 20

What happens during the recrystallization of sodium ethanoate in a hand warmer?

Answer 20

During the recrystallization of sodium ethanoate in a hand warmer, energy is transferred from the reaction system to the surroundings

Question 21

Where are exothermic reactions also used, other than in chemical hand and body warmers?

Answer 21

Other than in chemical hand and body warmers, exothermic reactions are also used in self-heating cans that makes drinks like hot coffee without any external heating device, like a kettle

Question 22

Other than in chemical hand and body warmers, exothermic reactions are also used in self-heating cans that makes drinks like hot coffee without any external heating device (like a kettle).
What is the reaction used to transfer energy to the food or drink usually?

Answer 22

The reaction used to transfer energy to the:
1. Food
Or,
2. Drink
is usually:
Calcium oxide + Water —> Calcium hydroxide

Question 23

How do self-heating cans work?

Answer 23

Self-heating cans work by you pressing a button in the base of the can

Question 24

What did development of the self-heating coffee can do?

Answer 24

Development of the self-heating coffee can:

1. Took years
2. Cost millions of pounds

Question 25

Development of the self-heating coffee can took years and cost millions of pounds. Even then, what was over a third of the can?

Answer 25

Even then, over a third of the can was taken up with the reactants needed to transfer enough energy to the coffee

Question 26

Development of the self-heating coffee can took years and cost millions of pounds. Even then, over a third of the can was taken up with the reactants needed to transfer enough energy to the coffee. Also, what happened in some early versions?

Answer 26

Also, in some early versions, the temperature of the coffee did not rise high enough in cold conditions

Question 27

Development of the self-heating can in the USA took how many years?

Answer 27

Development of the self-heating can in the USA took about 10 years

Question 28

What can be used to cool things down?

Answer 28

Endothermic processes can be used to cool things down

Question 29

Endothermic processes can be used to cool things down. | Example

Answer 29

For example, chemical cold packs usually contain: 1. Ammonium nitrate 2. Water ,sometimes present in a gel

Question 30

Endothermic processes can be used to cool things down. For example, chemical cold packs usually contain ammonium nitrate and water, sometimes present in a gel What happens when ammonium nitrate dissolves?

Answer 30

When ammonium nitrate dissolves, it absorbs energy from its surroundings

Question 31

Chemical cold packs usually contain ammonium nitrate and water. When ammonium nitrate dissolves, it absorbs energy from its surroundings, making them colder. Why are chemical cold packs used?

Answer 31

Chemical cold packs are used as emergency treatment for sports injuries

Question 32

Chemical cold packs usually contain ammonium nitrate and water. How are the ammonium nitrate and water kept in the chemical cold pack?

Answer 32

The: 1. Ammonium nitrate 2. Water are kept separate in the pack

Question 33

Chemical cold packs usually contain ammonium nitrate and water. The ammonium nitrate and water (sometimes present in a gel) are kept separate in the pack. What happens when squeezed or struck?

Answer 33

``` When: 1. Squeezed Or, 2. Struck ,the bag inside the water pack breaks ```

Question 34

How often can instant cold packs be used?

Answer 34

Instant cold packs can only be used once

Question 35

Instant cold packs can only be used once, but when are they ideal?

Answer 35

Instant cold packs can only be used once, but they are ideal where there is no ice available to treat a: 1. A knock Or, 2. Strain

Question 36

Instant cold packs can only be used once, but they are ideal where there is no ice available to treat a knock or strain. Where are instant cold packs often included?

Answer 36

Instant cold packs are often included in the first aid kit at venues used for: 1. Amateur sports Or, 2. Outdoor pursuits

Question 37

Endothermic processes can be used to cool things down. For example, chemical cold packs usually contain ammonium nitrate and water. What can the same endothermic change also be used to do?

Answer 37

The same endothermic change can also be used to chill cans of drinks

Question 38

When can instant cold packs be applied?

Answer 38

Instant cold packs can be applied as soon as an injury occurs to minimise damage

Question 39

Some hand warmers can only be used once. These hand warmers make use of the energy transferred to the surroundings in the oxidation of iron. Sodium chloride (common salt) is used as a catalyst. This type of hand warmer is disposable. It can be used only once, but it what?

Answer 39

It can be used only once, but it lasts for hours

Question 40

Some hand warmers can be used many times. These hand warmers are based on the formation of crystals from solutions of a salt. The salt used is often sodium ethanoate. A supersaturated solution is prepared by dissolving as much of the salt as possible in hot water. The solution is then what?

Answer 40

The supersaturated solution is then allowed to cool

Question 41

Some hand warmers can be used many times. These hand warmers are based on the formation of crystals from solutions of a salt. A small metal disk in the plastic pack is used to start the exothermic change. When you press the small metal disk a few times, small particles of metal are scraped off. These do what?

Answer 41

``` These: 1. 'Seed' Or, 2. Start off the crystallisation ```

Question 42

Some hand warmers can be used many times. These hand warmers are based on the formation of crystals from solutions of a salt. A small metal disk in the plastic pack is used to start the exothermic change. When you press the small metal disk a few times, small particles of metal are scraped off. These 'seed' (or start off) the crystallisation. The crystals spread throughout the solution, transferring energy to the surroundings in an exothermic change. They work for how long?

Answer 42

They work for about 30 minutes

Question 43

Some hand warmers can be used many times. These hand warmers are based on the formation of crystals from solutions of a salt. To reuse the warmer, you simply put the solid pack into boiling water to re-dissolve the crystals. Once it has cooled down, the pack is what?

Answer 43

Once it has cooled down, the pack is ready to activate again

Question 44

During the recrystallization of sodium ethanoate in a hand warmer, energy is transferred from the reaction system to the surroundings, increasing what?

Answer 44

During the recrystallization of sodium ethanoate in a hand warmer, energy is transferred from the reaction system to the surroundings, increasing the temperature of the surroundings, your hand

Question 45

Self-heating cans work by you pressing a button in the base of the can. This does what?

Answer 45

You pressing a button in the base of the can breaks a seal and lets the water and calcium oxide mix

Question 46

Self-heating cans work by you pressing a button in the base of the can. You pressing a button in the base of the can breaks a seal and lets the water and calcium oxide mix. Then what?

Answer 46

Then the exothermic reaction can begin

Question 47

Endothermic processes can be used to cool things down. For example, chemical cold packs usually contain ammonium nitrate and water. When ammonium nitrate dissolves, it absorbs energy from its surroundings, doing what?

Answer 47

When ammonium nitrate dissolves, it absorbs energy from its surroundings, making them colder

Question 48

Chemical cold packs usually contain ammonium nitrate and water. When ammonium nitrate dissolves, it absorbs energy from its surroundings, making them colder. Why are chemical cold packs used as emergency treatment for sports injuries?

Answer 48

Chemical cold packs are used as emergency treatment for sports injuries, because the decrease in temperature: 1. Reduces swelling 2. Numbs pain

Question 49

Chemical cold packs usually contain ammonium nitrate and water. The ammonium nitrate and water (sometimes present in a gel) are kept separate in the pack. When squeezed, or struck, the bag inside the water pack breaks, releasing what?

Answer 49

``` When: 1. Squeezed Or, 2. Struck ,the bag inside the water pack breaks, releasing ammonium nitrate ```

Question 50

Chemical cold packs usually contain ammonium nitrate and water. The ammonium nitrate and water (sometimes present in a gel) are kept separate in the pack. When squeezed, or struck, the bag inside the water pack breaks, releasing ammonium nitrate. The instant cold packs work for how long?

Answer 50

The instant cold packs work for about 20 minutes