PHYSICAL AND CHEMICAL CHANGES

Evaporation and condensation are the main processes in the water cycle.

What types of changes are these two processes?

• chemical and irreversible

   

                   

•   physical and irreversible                 

• physical and reversible

We can recycle waste materials to care for the environment.
Some types of metal are examples of materials that can be recycled.
In the process of recycling, the metal is cut into smaller pieces and melted.
It is then made into new objects.

 

Which of these describes the changes that the metal goes through during recycling?

• They are physical changes that can be reversed.

• They are physical changes that cannot be reversed.

• They are chemical changes that can be reversed.

Many changes happen in our everyday lives. The examples of reversible changes are...

• boiling an egg

   

• burning wood

• dissolving sugar in water

• stretching a rubber band

Many changes happen in our everyday lives. The examples of irreversible changes are...

• boiling an egg

   

• burning wood

• dissolving sugar in water

• stretching a rubber band

In a chemical reaction, substances called ______________ interact to form one or more new substances called ______________.

• gases, liquid

• liquid, gas

• products, reactants

• reactants, products

There are signs that a chemical reaction has taken place.

Which are some signs of chemical reactions?
Choose the two correct answers.

 

• change in colour

• change in shape

• change in temperature

An egg is placed in a glass of vinegar. Bubbles of carbon dioxide are formed on the eggshell.

From the information given, choose the correct two reactants and one product in the reaction

• Reactants: Vinegar and carbon dioxide | Product: Eggshell

• Reactants: Water and eggshell | Product: Oxygen
  

• Reactants: Eggshell and carbon dioxide | Product: Vinegar

• Reactants: Vinegar and eggshell | Product: Carbon dioxide

An egg is placed in a glass of vinegar. Bubbles of carbon dioxide are formed on the eggshell.

From the information given, What evidence proves that a chemical reaction has taken place?

• The egg changes color.
  

• A gas is given out.
  

• The vinegar turns into a solid.
  

• The egg becomes heavier.

Sid is making tea. He adds some tea leaves to a glass of hot water.
When he adds lemon juice to the tea, the colour of the tea changes from brown to yellow-brown.

 

(a)  Why is adding lemon juice to tea a chemical change?

• The tea becomes colder.

• The tea leaves dissolve completely.

• One or more new substances have been formed.

• The color change is temporary.

Sid is making tea. He adds some tea leaves to a glass of hot water.
When he adds lemon juice to the tea, the colour of the tea changes from brown to yellow-brown.

 The color change is temporary. How can you tell that a chemical reaction has taken place?

• The tea cools down.
  
  
  

• There is a color change.

• The tea becomes sweeter.

• The tea leaves disappear.