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Science Year 7 Chemical Reactions
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Chemical Equations

In a chemical reaction new substances are made. Reactions can be represented by a chemical equation.

'Chemical Equations' worksheet

Key stage:  KS 3

Curriculum topic:  Chemistry: Chemical Reactions

Curriculum subtopic:  Formulae and Equations

Difficulty level:  

down

Worksheet Overview

QUESTION 1 of 10

Chemical reactions happen everyday:

 

 from the burning of petrol in car engine...

 

   ...to the rusting of iron.

 

There are millions of reactions taking place every second of everyday.

 

Chemical reactions involve the production of one or more new substances called products. Word equations are used in chemistry to show the things that react, called reactants, and the new substances produced, which are called products.

 

Reactants    Products

 

For example, if magnesium metal is burned in oxygen, magnesium oxide is produced. This can be represented as a word equation:

 

Magnesium + Oxygen   Magnesium oxide

 

Word equations like these are used a lot in science as a quick way of representing a chemical reaction.

 

Most chemical reactions are irreversible. This means that once the reaction has taken place it is very difficult to get the reactants back.

Think how difficult it would be to turn the fumes from the exhaust pipe of a car back into petrol!

What name is given to the new substances produced by a chemical reaction?

Reactants

Products

Chemicals

What name is given to the substances that combine during a chemical reaction to form one or more new substances?

Reactants

Products

Chemicals

Using the table below to classify each of the reactions shown as fast, slow or very slow.

 Fast Slow Very Slow
Petrol burning
Car rusting
Milk going sour
Match burning
Explosion

Read this description of an experiment carefully:

 

A scientist places some sodium metal in water and stands back. Quickly he observes lots of smoke and flames being produced. Once the experiment is complete tests show that both the compound sodium hydroxide and hydrogen gas were produced by the reaction.

 

Use this information to complete the table below.

 Reactant Product
Sodium hydroxide
Sodium
Water
Hydrogen

Read this description of an experiment carefully:

 

Some magnesium metal is placed into a test tube of hydrochloric acid and immediately bubbles of hydrogen gas can be seen and the test tube begins to heat up. Magnesium chloride is also produced in this reaction.

 

Use this information to complete the table below.

 Reactant Product
Magnesium
Hydrogen
Hydrochloric acid
Magnesium chloride

Use the table below to complete these word equations.

Enter your answers in lower case.

 

A + Oxygen  Magnesium oxide

Sodium + Oxygen  B

Calcium + C  Calcium oxide

 Answer
A
B
C

Complete the table below to show which changes are chemical reactions and which are not.

 Chemical Reaction No Reaction
Water boiling
Egg frying
Salt dissolving
Candle burning
  • ANSWERS
  • Question 1

What name is given to the new substances produced by a chemical reaction?

CORRECT ANSWER
Products
EDDIE SAYS
A chemical reaction involves the combining of reactants to form one or more new substances called products.
  • ANSWERS
  • Question 2

What name is given to the substances that combine during a chemical reaction to form one or more new substances?

CORRECT ANSWER
Reactants
EDDIE SAYS
A chemical reaction involves the combining of reactants to form one or more new substances called products.
  • ANSWERS
  • Question 3

Using the table below to classify each of the reactions shown as fast, slow or very slow.

CORRECT ANSWER
 Fast Slow Very Slow
Petrol burning
Car rusting
Milk going sour
Match burning
Explosion
EDDIE SAYS
Reactions occur very quickly (such as in an explosion) or very slowly (such as a car rusting). Scientists can alter how quickly reactions happen.
  • ANSWERS
  • Question 4

Read this description of an experiment carefully:

 

A scientist places some sodium metal in water and stands back. Quickly he observes lots of smoke and flames being produced. Once the experiment is complete tests show that both the compound sodium hydroxide and hydrogen gas were produced by the reaction.

 

Use this information to complete the table below.

CORRECT ANSWER
 Reactant Product
Sodium hydroxide
Sodium
Water
Hydrogen
EDDIE SAYS
Descriptions of experiments must be read carefully to identify both the reactants and the products. Remember, only the chemicals involved in the reaction are included. Fire, for example, is not a chemical - it is infact a form of energy, so is not included in equations.
  • ANSWERS
  • Question 5

Read this description of an experiment carefully:

 

Some magnesium metal is placed into a test tube of hydrochloric acid and immediately bubbles of hydrogen gas can be seen and the test tube begins to heat up. Magnesium chloride is also produced in this reaction.

 

Use this information to complete the table below.

CORRECT ANSWER
 Reactant Product
Magnesium
Hydrogen
Hydrochloric acid
Magnesium chloride
EDDIE SAYS
Descriptions of experiments must be read carefully to identify both the reactants and the products. Remember only the chemicals involved in the reaction are included. Heat, for example, is not a chemical - it is infact a form of energy, so is not included in equations.
  • ANSWERS
  • Question 6

Use the table below to complete these word equations.

Enter your answers in lower case.

 

A + Oxygen  Magnesium oxide

Sodium + Oxygen  B

Calcium + C  Calcium oxide

CORRECT ANSWER
 Answer
A
B
C
EDDIE SAYS
Each equation gives you a clue to the answer of the other equations.
  • ANSWERS
  • Question 7

Complete the table below to show which changes are chemical reactions and which are not.

CORRECT ANSWER
 Chemical Reaction No Reaction
Water boiling
Egg frying
Salt dissolving
Candle burning
EDDIE SAYS
The best way to identify a chemical reaction is to think about how easy it would be to reverse the change, for example you can turn steam back into water so it is unlikely to be a chemical reaction but you can't unfry an egg so this is a chemical reaction.
---- OR ----

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