NCERT solutions for Science [English] Class 7 chapter 5 - Physical and Chemical Changes [Latest edition]

Classify the changes involved in the following process as physical or chemical changes:

Photosynthesis

Classify the changes involved in the following process as physical or chemical changes:

Dissolving sugar in water

Classify the changes involved in the following process as physical or chemical changes:

Burning of coal

Classify the changes involved in the following process as physical or chemical changes:

Melting of wax

Classify the changes involved in the following process as physical or chemical changes:

Beating aluminium to make aluminium foil

Classify the changes involved in the following process as physical or chemical changes:

Digestion of food

State whether the following statement is true or false. In case a statement is false, write the corrected statement.

Cutting a log of wood into pieces is a chemical change.

State whether the following statement is true or false. In case a statement is false, write the corrected statement.

Formation of manure from leaves is a physical change.

State whether the following statement is true or false. In case a statement is false, write the corrected statement.

Iron pipes coated with zinc do not get rusted easily.

State whether the following statement is true or false. In case a statement is false, write the corrected statement.

Iron and rust are the same substances. 

State whether the following statement is true or false. In case a statement is false, write the corrected statement.

Condensation of steam is not a chemical change.

When carbon dioxide is passed through lime water, it turns milky due to the formation of ______.

The chemical name of baking soda is ______.

Two methods by which rusting of iron can be prevented are ______ and ______.

Changes in which only ______ properties of a substance change are called physical changes.

Changes in which new substances are formed are called ______ changes.

When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.

When a candle burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.

How would you show that setting of curd is a chemical change?

Explain why burning of wood and cutting it into small piece are considered as two different types of changes.

Describe how crystals of copper sulphate are prepared.

Explain how painting of an iron gate prevents it from rusting.

Explain why rusting of iron objects is faster in coastal areas than in deserts.

The gas we use in the kitchen is called liquefied petroleum gas (LPG). In the cylinder, it exists as a liquid. When it comes out from the cylinder it becomes a gas (Change − A), then it burns (Change − B). The following statements pertain to these changes. Choose the correct one.

Anaerobic bacteria digest animal waste and produce biogas (Change – A). The biogas is then burnt as fuel (Change – B). The following statements pertain to these changes. Choose the correct one.

Describe two changes that are harmful. Explain why you consider them harmful. How can you prevent them?

Take three glass bottles with wide mouths. Label them A, B, and C. Fill about half of the bottle A with ordinary tap water. Fill bottle B with water which has been boiled for several minutes, to the same level as in A. In bottle C, take the same boiled water and of the same amount as in other bottles. In each bottle put a few similar iron nails so that they are completely under water. Add a teaspoonful of cooking oil to the water in bottle C so that it forms a film on its surface. Put the bottles away for a few days. Take out nails from each bottle and observe them. Explain your observations.

Prepare crystals of alum.

Collect information about the types of fuels used for cooking in your area. Discuss with your teachers/parents/others which fuels are less polluting and why.