Advertisements
Advertisements
Question
Define a chemical change. Give two examples of the above changes.
Advertisements
Solution
A permanent change in which new substances are formed whose composition and properties are completely different from those of the original
substances.
Chemical change:
(i) Burning of wood.
(ii) Breathing.
RELATED QUESTIONS
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.
Explain why burning of wood and cutting it into small piece are considered as two different types of changes.
Fill in the blank
Revolution of the earth around the sun is a ________ change.
State whether the following is physical or chemical changes.
water cycle in nature —
State whether the following is physical or chemical changes.
Slaking of lime —
Tick (√) the correct alternative from the choice given for the following statement.
A substance which can not sublime is
Sublimation is classified as a physical change. Why ?
Classify the following as physical or chemical change :
Formation of curd from milk
Classify the following as a physical or a chemical change.
Manufacture of salt from sea water
Fill in the blank with the appropriate word of the statement given below:
Germination of seeds is considered a __________ change.
State whether the following statement is true or false. If false write the correct statement.
Melting of ice is an exothermic, irreversible chemical change.
Match the examples of changes in List I with the correct.
| List I | List II |
| 1. Expansion of a steel rod on heating | A: Physical change |
| 2. Rotting of eggs | B: Chemical change |
| 3. Milk turning sour | |
| 4. Tarnishing of copper | |
| 5. Separation of naphthalene from a mixture of naphthalene and sodium chloride. |
State which of the following pertain to – chemical changes.
- Substance retains its identity.
- The change is permanent.
- No new substance is formed.
- Is easily reversible.
- Produces one or more new substances by a change in its composition.
- The change is temporary.
- The composition and properties of the original substance are not altered.
State which of the following terms connected with change of state of matter i.e.
(a) Melting
(b) Vaporisation
(c) Condensation
(d) Freezing
pertain to –
- Conversion of a liquid into a vapour or gas.
- Conversion of a liquid into a solid.
- Conversion of a solid into a liquid on heating.
Match the examples of changes in List I with the correct type of change in List II.
| List I | List II |
| 1. Burning of paper | A: Physical change |
| 2. The ringing of an electric bell | B: Chemical change |
| 3. Curdling of milk | |
| 4. Electric light is switched on | |
| 5. Melting of butter |
Which of the following is a physical change?
Paheli’s mother made a concentrated sugar syrup by dissolving sugar in hot water. On cooling, crystals of sugar got separated. This indicates a –
Give two examples for the following case:
Physical changes which are not reversible
If you leave a piece of iron in the open for a few days, it acquires a film of brownish substance, called rust.
Do you think rust is different from iron?
The change of state of a substance from solid to liquid and liquid to gas is ______.
