Physical and Chemical Changes — Question 1
Back to all questionsQuestion 1
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.
(a) Desirable and undesirable change
(b) Periodic and non-periodic change
(c) Slow and fast change
(d) Natural and man-made change
(e) Reversible and irreversible change
(a) Difference between desirable and undesirable change :
| Desirable change | Undesirable change |
|---|---|
| Desirable changes produce good results. | Undesirable changes are unfavorable. |
| For example, rain bringing water to crops is a desirable change. | For example, rain causing destruction by floods is an undesirable change. |
(b) Difference between periodic and non-periodic change :
| Periodic change | Non - Periodic change |
|---|---|
| Changes which occur periodically at regular intervals of time. | Changes which do not occur periodically [do not repeat] at regular intervals of time. |
| For example, change of seasons is a periodic change | For example, change of weather is a non-periodic change. |
(c) Difference between slow and fast change
| Slow change | Fast change |
|---|---|
| Change which occur very slowly over days, months and years. | Change which occur very rapidly in seconds or minutes. |
| For example, the growth of a tree from a seed | For example, occurring of lightning. |
(d) Difference between natural and man-made change
| Natural change | Man-made change |
|---|---|
| Changes brought about by nature. | Changes brought by man |
| For example, growth in man and plants. | For example, conversion of iron to steel. |
(e) Difference between reversible and irreversible change
| Reversible change | Irreversible change |
|---|---|
| Changes which are temporary and can be reversed by change in conditions. | Changes which are permanent and cannot be reversed by change in conditions. |
| For example, melting of ice and freezing of water. | For example, burning of paper. |
ICSE Class VII Chemistry Chapter 2 12 Marks
Physical and Chemical Changes — Quick Study Guide
Changes around us are classified as physical (no new substance formed) or chemical (new substance formed). Understanding the difference is fundamental to chemistry.
Key Definitions
- Physical change: No new substance formed, usually reversible (e.g., melting ice, dissolving sugar)
- Chemical change: New substance formed, usually irreversible (e.g., burning, rusting, cooking)
- Exothermic: Reaction that releases heat (e.g., burning fuel)
- Endothermic: Reaction that absorbs heat (e.g., photosynthesis)
Six Signs of Chemical Change
Colour change, gas evolution, temperature change, precipitate formation, smell change, light/sound emission.
Exam Tips
- Burning a candle = BOTH physical and chemical change
- Dissolving salt/sugar in water = physical change (recoverable)
- Not all physical changes are reversible (tearing paper)
- Learn the comparison table (6 differences) thoroughly
Bright Tutorials | ICSE Class VII Chemistry | Chapter 2: Physical and Chemical Changes | Contact: 9403781999