Class 7 Science - Chapter Physical and Chemical Changes NCERT Solutions | Explain why burning of wood and cutting

Classify the changes involved in the following processes as physical or chemical changes:
(a) Photosynthesis
(b) Dissolving sugar in water
(c) Burning of coal
(d) Melting of wax
(e) Beating aluminium to make aluminium foil
(f ) Digestion of food

Describe how crystals of copper sulphate are prepared.

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

State whether the following statements are true or false. In case a statement is false, write the corrected statement in your notebook.

(a) Cutting a log of wood into pieces is a chemical change. (True/False)
(b) Formation of manure from leaves is a physical change. (True/False)                                                                                                                                              (c) Iron pipes coated with zinc do not get rusted easily. (True/False)
(d) Iron and rust are the same substances. (True/False)
(e) Condensation of steam is not a chemical change. (True/False)

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

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?

The gas we use in the kitchen is called liquified petroleum gas (LPG). In the cylinder it exist 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.

(i) Process – A is a chemical change.
(ii) Process – B is a chemical change.
(iii) Both processes A and B are chemical changes.
(iv) None of these processes is a chemical change.

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

Fill in the blanks in the following statements:

(a) When carbon dioxide is passed through lime water, it turns milky due to the formation of _________.
(b) The chemical name of baking soda is _________.
(c) Two methods by which rusting of iron can be prevented are _________ and _________.
(d) Changes in which only _________ properties of a substance change re called physical changes.
(e) Changes in which new substances are formed are called _________ changes.

State similarities and differences between the laboratory thermometer and the clinical thermometer.

State differences between acids and bases.

Name the elements that determine the weather of a place.

Fill the missing word in the blank spaces in the following statements:

(a) Wind is——————air.
(b) Winds are generated due to —————— heating on the earth.
(c) Near the earth’s surface __________air rises up whereas ___________ air comes down.
(d) Air moves from a region of ——— pressure to a region of ———.

In addition to the rock particles, the soil contains

(i) air and water
(ii) water and plants
(iii) minerals, organic matter, air and water
(iv) water, air and plants

Why does an athlete breathe faster and deeper than usual after finishing the race?

Match structures given in Column I with functions given in Column II.

Column I                           Column II
(i) Stomata                        (a) Absorption of water
(ii) Xylem                           (b) Transpiration
(iii) Root hairs                    (c) Transport of food
(iv) Phloem                        (d) Transport of water
                                          (e) Synthesis of carbohydrates

Fill in the blanks:

(a) Production of new individuals from the vegetative part of parent is called_____________.
(b) A flower may have either male or female reproductive parts. Such a flower is called_____________.
(c) The transfer of pollen grains from the anther to the stigma of the same or of another flower of the same kind is known as _____________.
(d) The fusion of male and female gametes is termed as _____________.
(e) Seed dispersal takes place by means of _____________, _____________ and _____________.

Classify the following as motion along a straight line, circular or oscillatory motion:

(i) Motion of your hands while running.
(ii) Motion of a horse pulling a cart on a straight road.
(iii) Motion of a child in a merry-go-round.
(iv) Motion of a child on a see-saw.
(v) Motion of the hammer of an electric bell.
(vi) Motion of a train on a straight bridge.

Why do organisms need to take food?

Here is a crossword puzzle: Good luck!

Across
3. Liquid waste products
4. Solid waste extracted in sewage treatment
6. A word related to hygiene
8. Waste matter discharged from human body

Down
1. Used water
2. A pipe carrying sewage
5. Micro-organisms which causes cholera
7. A chemical to disinfect water

Where is the bile produced? Which component of the food does it help to digest?

An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will

(a) flow from iron ball to water.
(b) not flow from iron ball to water or from water to iron ball.
(c) flow from water to iron ball.
(d) increase the temperature of both.

Mark ‘T’ if the statement is true and ‘F’ if it is false:

(i) Nitric acid turn red litmus blue. (T/F)
(ii) Sodium hydroxide turns blue litmus red. (T/F)
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T/F)
(iv) Indicator is a substance which shows different colours in acidic and basic solutions. (T/F)
(v) Tooth decay is caused by the presence of a base. (T/F)

Fill in the blanks:
(a) Green plants are called _________________ since they synthesise their own food.
(b) The food synthesised by the plants is stored as _________________.
(c) In photosynthesis solar energy is captured by the pigment called ___________.
(d) During photosynthesis plants take in ______________________ and release __________________.

David is observing his image in a plane mirror. The distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be

(i) 3 m        (ii) 5 m
(iii) 6 m      (iv) 8 m

Fill in the blanks:
(a) The main steps of nutrition in humans are __________, __________, __________, _________ and __________.
(b) The largest gland in the human body is __________.
(c) The stomach releases hydrochloric acid and ___________ juices which act on food.
(d) The inner wall of the small intestine has many finger-like outgrowths called _________.
(e) Amoeba digests its food in the ____________ .

Give one use each of a concave and a convex mirror.

Why do we often sneeze when we inhale a lot of dust-laden air?

Match the items in Column I with those in Column II:
Column I                             Column II
(a) Yeast                             (i) Earthworm
(b) Diaphragm                    (ii) Gills
(c) Skin                               (iii) Alcohol
(d) Leaves                          (iv) Chest cavity
(e) Fish                               (v) Stomata
(f) Frog                               (vi) Lungs and skin
                                           (vii) Tracheae