Non-reversible Changes Worksheet

Melting and freezing are REVERSIBLE changes. This means that if we undo the change, we can get back the materials we started with. A good example of this is ICE and WATER.

Remember that in Science, MATERIAL means any solid, liquid or gas that you can detect using your senses! Non-reversible changes result in a NEW and DIFFERENT material.

Birthday cake

Birthday cake is a good example of a NEW MATERIAL. We mix together eggs, butter, flour and sugar, add heat and enjoy! BUT... we cannot reverse the changes. 'Cake' cannot be changed back into the ingredients we started with. We wouldn't want to anyway!

Many non-reversible changes are caused by HEATING. So, let's find out about non-reversible changes...

Gita and Jasa are carrying-out some science investigations. They are checking their understanding of REVERSIBLE reactions.

Gita takes an ice lolly out of the freezer and leaves it on the kitchen table.

Ice lolly

Which change do you think takes place?

freezing

evaporating

melting

condensing

Jasa uses an aerosol air freshener. He sprays some into the air.

He says, 'This change can be reversed.'

Can of air freshener

Is he correct?

yes

no

Gita breaks an egg into a bowl and whisks it with a fork.

Which of these best describes a beaten egg?

solid

liquid

gas

Jasa cooks the egg.

The heat changes the liquid egg into a...

gas

solid

pizza

In separate beakers, Gita mixes salt, sugar and coffee granules with water. They make liquids which are called SOLUTIONS (with no solid left on the bottom).

Help Gita choose the scientific word which describes this change.

dissolving

mixing

condensing

Gita and Jasa look in their fridge. They know that butter and yogurt are made from milk.

bUTTER

When milk is turned into new foods, we can describe the change as...

melting

reversible

non-reversible

tasty

The students know that heating some solids results in non-reversible reactions.

Which THREE of these are made by non-reversible reactions?

melted chocolate

bread

yorkshire puddings

cup cakes

Gita thinks that they should extend their investigations to other materials around them.

They decide to have a bar-be-que. Yippee!

Mum has built a bar-be-que in the garden using bricks and concrete.

Bricks and concrete are examples of materials resulting from what type of change?

reversible reactions

non-reversible reactions

Jasa puts the charcoal on the bar-be-que.

Charcoal briquettes

Charcoal is a material made by a non-reversible reaction. Which material is irreversibly changed to produce charcoal?

coal

clay

wood

Jasa and Gita enjoy eating the food cooked on their bar-be-que.

Burger in a bun

They think about what they have learned. Can you help them remember the FOUR non-reversible ways of changing materials from this list?

Tick the FOUR you think are non-reversible changes.

dissolving

frying

baking

grilling

melting

burning

ANSWERS

Question 1

Gita and Jasa are carrying-out some science investigations. They are checking their understanding of REVERSIBLE reactions.

Gita takes an ice lolly out of the freezer and leaves it on the kitchen table.

Ice lolly

Which change do you think takes place?

CORRECT ANSWER

melting

EDDIE SAYS

The ice lolly melts - that means the solid ice turns into a sticky liquid mess! Freezing is the exact opposite (liquid to solid) while evaporating is when a liquid turns into a gas (condensing is the opposite of this.)

ANSWERS

Question 2

Jasa uses an aerosol air freshener. He sprays some into the air.

He says, 'This change can be reversed.'

Can of air freshener

Is he correct?

CORRECT ANSWER

yes

EDDIE SAYS

The liquid in the can evaporates and tuns into a smelly gas as it's squirted into the air. If Jasa could collect the gas and condense it, he would have the material he started with! Tough to do, but definitely possible.

ANSWERS

Question 3

Gita breaks an egg into a bowl and whisks it with a fork.

Which of these best describes a beaten egg?

CORRECT ANSWER

liquid

EDDIE SAYS

OK! It's a bit gloopy, but beaten egg 'flows' and takes on the shape of its container. The gas Gita has beaten into it makes the surface bubbles.

ANSWERS

Question 4

Jasa cooks the egg.

The heat changes the liquid egg into a...

CORRECT ANSWER

solid

EDDIE SAYS

The heat has turned the egg into a new material which is solid. Jasa cannot change the egg back to liquid, raw egg. It's a permanent (non-reversible) change.

ANSWERS

Question 5

In separate beakers, Gita mixes salt, sugar and coffee granules with water. They make liquids which are called SOLUTIONS (with no solid left on the bottom).

Help Gita choose the scientific word which describes this change.

CORRECT ANSWER

dissolving

EDDIE SAYS

When the solid cannot be seen, making a clear (maybe coloured) liquid, the REVERSIBLE change is dissolving. The solid becomes tiny, tiny particles, spread out throughout the solution. Mixing is nearly correct, as the solid and liquid are mixed, but there's a special word for this mixing, when the solid DISSOLVES in the liquid to make a solution.

ANSWERS

Question 6

Gita and Jasa look in their fridge. They know that butter and yogurt are made from milk.

bUTTER

When milk is turned into new foods, we can describe the change as...

CORRECT ANSWER

non-reversible

EDDIE SAYS

Milk cannot be separated from butter or yogurt, because yogurt and butter are the result of non-reversible reactions! Can you think of any other products made from non-reversible reactions starting with milk?

ANSWERS

Question 7

The students know that heating some solids results in non-reversible reactions.

Which THREE of these are made by non-reversible reactions?

CORRECT ANSWER

bread
yorkshire puddings
cup cakes

EDDIE SAYS

Heating changes materials. We use heat to cook mixtures of materials to make new, tasty foods. Melted chocolate is still chocolate - put it in the fridge and it goes solid again. The other three all started as a liquid mixture, like batter, but the heat of the cooking process has changed them permanently - that's non-reversible.

ANSWERS

Question 8

Gita thinks that they should extend their investigations to other materials around them.

They decide to have a bar-be-que. Yippee!

Mum has built a bar-be-que in the garden using bricks and concrete.

Bricks and concrete are examples of materials resulting from what type of change?

CORRECT ANSWER

non-reversible reactions

EDDIE SAYS

Cement is a mixture of sand, limestone, clay and water. The changes which take place in this mixture cannot be reversed. When brick clay is 'fired' to a very high temperature, it changes into brick, another non-reversible reaction!

ANSWERS

Question 9

Jasa puts the charcoal on the bar-be-que.

Charcoal briquettes

Charcoal is a material made by a non-reversible reaction. Which material is irreversibly changed to produce charcoal?

CORRECT ANSWER

wood

EDDIE SAYS

Charcoal is made by heating wood to a high temperature, but not allowing it to catch fire! It's done in a special stack which is covered with earth to cut down the air getting in. Then, as it burns slowly, the wood turns into charcoal rather than ash.

ANSWERS

Question 10

Jasa and Gita enjoy eating the food cooked on their bar-be-que.

Burger in a bun

They think about what they have learned. Can you help them remember the FOUR non-reversible ways of changing materials from this list?

Tick the FOUR you think are non-reversible changes.

CORRECT ANSWER

frying
baking
grilling
burning

EDDIE SAYS

Dissolving is mixing a solid and liquid and you can separate them by evaporation, while melting can be reversed by freezing. The other four are non-reversible changes, resulting in new substances which cannot be turned back into what you started with.