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Chemical Reactions

In this worksheet, students will explore how chemical change and reactions take place, as well as different types of chemical reactions.

'Chemical Reactions' worksheet

Key stage:  KS 4

Curriculum topic:  Chemistry: Energy Changes in Chemistry

Curriculum subtopic:  Measurement of Energy Changes in Chemical Reactions

Difficulty level:  

Worksheet Overview

QUESTION 1 of 10

Cooking food is a chemical reaction that takes place everyday in most households. A chemical reaction, such as cooking an egg is an irreversible change, because we cannot bring the egg back to its original raw state. A physical change is one that can be reversed; for example, we can boil water and then let it cool again. This is called a reversible change.

 

Chemical reactions are irreversible changes. Some of them take place when a substance decomposes (breaks down) when heated. An example of this is the thermal decomposition of sodium hydrogencarbonate, comonly known as baking powder. We can show this reaction using a chemical equation:

 

 

 

We use baking powder in baking, because when it is heated it produces carbon dioxide, a gas that gets trapped in the dough and makes it rise.

Burning fuels (oil, wood, gas and even paper) is also a chemical reaction:

 

fuel + oxygen carbon dioxide + water

 

The scientific name for burning is combustion.

Some reactions are exothermic, which means they release heat. An example of this is combustion. However, some reactions need energy to take place and these are called endothermic. An example of endothermic reactions is photosynthesis in plants, where energy from the Sun is taken in. 

 

 

Group 1 elements of the Periodic table (shown below, click on it to see a larger version) react with water to produce hydroxides, which are alkalis:

lithium + water lithium hydroxide + hydrogen

 

Group 7 elements can react with Group 1 elements in the following way:

sodium + chlorine sodium chloride

 

 

Chemical reactions occur because elements either share or give/take electrons to/from each other. The bonds between atoms weaken and break and that's how new substances are formed. Elements or compounds before the arrow are called reactants, whereas after the arrow are called products.

Tick whether the change is physical or chemical.

 Physical Chemical
baking bread
melting ice
melting chocolate
burning paper

Is the following statement true or false?

 

A chemical reaction is an irreversible change.

True

False

What makes bread rise in the oven?

Carbon dioxide

Oxygen

Hydrogen

Which two of the following are produced when coal is burned?

Carbon dioxide

Oxygen

Water

Fire

What are the reactants when burning natural gas?

Carbon dioxide

Water

Natural gas

Oxygen

An endothermic reaction takes in heat from its surroundings. If you are holding a container when an endothermic reaction takes place, will your hand feel hot or cold?

Hot

Cold

What are the products of photosynthesis?

Carbon dioxide

Glucose

Water

Oxygen

What is the scientific name for burning?

Potassium is a Group 1 element. What will it produce if it reacts with water?

Carbon dioxide

Potassium hydroxide

Oxygen

Hydrogen

What breaks during a chemical reaction?

Atoms

Bonds

Ties

  • Question 1

Tick whether the change is physical or chemical.

CORRECT ANSWER
 Physical Chemical
baking bread
melting ice
melting chocolate
burning paper
EDDIE SAYS
Melted ice and chocolate can be solidified again if put in the freezer/fridge - this makes them phisical. Whereas we cannot turn bread into the raw dough again or form paper from its ashes, this makes them chemical.
  • Question 2

Is the following statement true or false?

 

A chemical reaction is an irreversible change.

CORRECT ANSWER
True
EDDIE SAYS
After the chemical reaction has taken place, we cannot get the reactants back again. This is because the particles have made something new.
  • Question 3

What makes bread rise in the oven?

CORRECT ANSWER
Carbon dioxide
EDDIE SAYS
Carbon dioxide is produced when baking powder decomposes from the heat in the oven and it is trapped in the dough, making it rise. This process is used in a lot of baking - and every time you use self-raising flour.
  • Question 4

Which two of the following are produced when coal is burned?

CORRECT ANSWER
Carbon dioxide
Water
EDDIE SAYS
Burning any fuel produces carbon dioxide and water. This is because most of the fuels we use are hydrocarbons made of only hydrogen and carbon.
  • Question 5

What are the reactants when burning natural gas?

CORRECT ANSWER
Natural gas
Oxygen
EDDIE SAYS
When burning a fuel, the reactants are the fuel itself and oxygen. Reactants are the stuff that you need to make the reaction happen and products are what you end up with.
  • Question 6

An endothermic reaction takes in heat from its surroundings. If you are holding a container when an endothermic reaction takes place, will your hand feel hot or cold?

CORRECT ANSWER
Cold
EDDIE SAYS
An endothermic reaction takes in heat from its surroundings, so you would feel cold because all the heat of the container would be used by the reaction. Exo(thermic) like exit means the heat will go out of the reaction. The other one then makes things cold. That's how I remember it.
  • Question 7

What are the products of photosynthesis?

CORRECT ANSWER
Glucose
Oxygen
EDDIE SAYS
  • Question 8

What is the scientific name for burning?

CORRECT ANSWER
combustion
EDDIE SAYS
Burning is called combustion in chemistry. This is because combustion describes the reaction - whereas burning could mean a lot of different types of reactions.
  • Question 9

Potassium is a Group 1 element. What will it produce if it reacts with water?

CORRECT ANSWER
Potassium hydroxide
Hydrogen
EDDIE SAYS
Group 1 elements produce their hydroxide (potassium hydroxide in this case) and hydrogen. Remember the general equation: metal + water -> metal hydroxide + hydrogen.
  • Question 10

What breaks during a chemical reaction?

CORRECT ANSWER
Bonds
EDDIE SAYS
Bonds between atoms break during chemical reactions and new bonds are formed. This is where the energy comes from or is released from.
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