Allied solutions simplified middle school chemistry class 7 Solutions for Chapter 2 physical and chemical changes

Q1) Change is the law of nature and occurs in our everyday life, at all times and in all places.

Differentiate between the following changes with a suitable example.

1. Desirable and undesirable change
2. Periodic and non-periodic change
3. Slow and fast change
4. Natural and man-made change
5. Reversible and irreversible change.

Q2) State whether the following statements are true or false. If false write – the correct statement.

1. Desirable changes are meaningful, while undesirable changes are unfavourable.
2. During physical changes, the composition od the original substance is not altered, but the properties of the original substance are altered.
3. During a chemical change the composition od the original substance is not altered and the change is irreversible.
4. Melting of butter and wax is an example of chemical changes.
5. Melting of ice is an exothermic, irreversible chemical change.

Q2) Differentiate between a physical change and a chemical change with reference to –

1. Nature of change i.e. temporary and reversible or permanent and irreversible.
2. Formation of products.
3. Energy change taking place during the respective change.

Q3) Give three reasons why the melting of wax is considered a physical change while burning a candle, a chemical change.

Q4) State the observation seen when milk in a dish is kept aside for a few hours or more. Is the change which occurs – a physical change or a chemical change. Give reasons.

Q5) State what is meant by the term – interconversion of matter. Is interconversion of matter a physical change or a chemical change.

Q6) Ice kept in a beaker, slowly melts and turns into water. The water in the beaker on solidification i.e. freezing turns back to ice. Give four reasons why the change from ice to water and water back to ice is considered a physical change.

Q7) Explain the term – ‘sublimation’. Is sublimation of naphthalene – a physical or a chemical change. Give reasons.

Q8) Ammonium Chloride is also a sublimable solid. Give a reason why sublimation of ammonium chloride involves a physical and a chemical change.

Q9) State why the addition of sodium chloride to water is considered a physical change, while the addition of dilute sulphuric acid to zinc is considered a chemical change.

Q10) Photosynthesis is a natural process by which green plants manufacture food in the presence of sunlight,

1. Are any new products formed during the above process.
2. Can the change be reversed or is it irreversible
3. State the conclusions which can be drawn, to represent photosynthesis as a physical or a chemical change.

Q11) Give reasons why – separation of mixtures e.g. iron from a mixture of iron and sulphur is a physical change, but heating a mixture of iron and sulphur is considered a chemical change.

Q12) Explain in brief the involvement of energy in – physical change and chemical changes.

Q1) Fill in the blanks with the appropriate words for each of the statements given below:

1. Germination of seeds is considered a _____ reaction.
2. If a change is permanent & irreversible it is considered a_ change.
3. Heating a piece of iron is considered a _____ change while heating a piece of coal (carbon) is considered a _____ change.
4. Chemical changes may involve the exchange of energy in the form of ____ and ____
5. Change of milk od curd is a _______ change.

Q3) Match the examples of changes in List I with the correct

Q4) Fill in the blanks with the correct words for each of the statements given below:

1. Sublimation is ______ a change of state of matter.
2. Sublimation involves a ______ change.
3. During sublimation, a solid on heating turns directly into _____ and on cooling back to _____
4. Ammonium chloride, a sublimable sold undergoes _______ on heating.
5. Sublimation of iodine is an example of _______ change.

Q5) Name the following

1. The product obtained during ‘photosynthesis’ – which is a chemical change.
2. The term involved in the change of state from – ”water to ice’ – which is a physical change.
3. The final product of the physical change involved during ‘melting of a piece of wax’
4. The type of change i.e. physical or chemical involved – ‘during respiration in human beings.’
5. The type of change i.e. physical or chemical involved – ‘when a substance undergoes a change in state, colour or size.