I. Multiple Choice Questions (MCQs).
Q.1. Rusting of iron is an example of
a) slow change
b) fast change
c) physical change
d) none of these
Answer. a) slow change
Q.2. Bursting of a cracker is an example of
a) fast change
b) man-made change
c) both (a) and (b)
d) slow change
Answer: a) fast change
Q.3. The example of irreversible change is/are
a) magnetisation of iron
b) formation of snow
c) respiration in animals
d) all of these
Answer c) respiration in animals
Q.4. If the substance can be brought back to its original form soon after the change, then this kind of change is called
c) fast change
d) slow change
Answer: a) reversible
Q.5. Cutting of paper is an example of
a) physical change
b) chemical change
c) reversible change
d) none of these
Answer: a) physical change
II. Fill in the blanks by selecting appropriate words from the given list :
List : structure, state, physical, shape, desirable
Q.1. Melting of wax near the wick of a candle is _______________ change.
Q.2. The _______________ of a balloon changes when we blow air in it.
Q.3. The _______________ of a seed changes when it grows into a flower.
Q.4. A change brought by nature or a person is called _______________ if it is useful
Q.5. During evaporation and condensation of water, the _______________ of water
Answer: 1- physical,
III. Match the items of Column A with those of Column B.
Ans. 1- c, 2- d, 3-b, 4-e, 5-a
IV. Write ‘T’ for the true and ‘F’ for the false statements.
Q.1. All the things present in the universe are changing constantly.
Q.2. Sugar and water kept separately can form solution.
Q.3. When milk forms curd its physical property changes.
Q.4. The change can be often reversed, to get back the original substance.
Q.5. Bursting of a balloon is an example of reversible change.
Ans. 1- T, 2-T, 3-F, 4-T, 5-F
V. Very Short Answer Questions.
Q.1. Name two examples of fast change.
Answer : Two example of fast changes are
• Bursting of a cracker and
• Bursting of a balloon
Q.2. What do you mean by desirable change?
Answer: A change brought by nature or a person is called desirable, if it is useful to us.
Q.3. Give two examples of the change which cannot be reversed.
Answer: burning of wood changing of milk to curd
Q.4. Write two examples of physical change.
Answer: Breaking of glass, cutting of paper,
Q.5. Write two examples of chemical change.
Answer: Burning of a candle Rusting of iron
VI. Short Answer Questions.
Q.1. Define slow change with an example.
Answer: The changes which take place in a long period of time are called slow changes. A baby takes many years to grow into an adult. Rusting of iron and germination of seeds take place in a few days.
Q.2. Describe how all changes require energy in some form or the other even though they are physical changes.
Answer: All form of changes require energy in some form or the other even though they are physical changes. For example, evaporation of water and melting of ice require energy in the form of heat. During condensation of water vapour heat is given out. To stretch a rubber band you require some force. Similarly, kicking a football,
Q.3. Define natural and desirable change with examples.
Answer: Change which is due to nature is known as natural change. Changes in the weather, occurrence of day and night, growth of plants and animals, ripening of fruit are all natural changes.
Q.4. Define natural and undesirable change with examples.
Answer: A change brought by nature and produces some harmful effects, it is called
undesirable change. Earthquakes, storms, floods, volcanic eruptions, erosion of land by sea are also some changes brought about by nature, which are undesirable. We have no control over such changes. These changes are undesirable since they damage property, important structures, crops and harm human beings and animals.
Q.5. Define physical change which is reversible. Explain with examples.
Answer: The melted ice cube may be refrozen, so melting is a reversible physical change
VII. Long Answer Questions.
Q.1. Describe physical change with proper examples in which various kinds of physical properties are changed.
Answer: A change is reversible if the substance can be brought back to its original form soon after the change is known as reversible change. Stretching a rubber band, squeezing a piece of sponge, blowing a balloon, folding a piece of paper to make a boat or a fan, melting of ice, freezing of water are all physical change which are reversible.
Q.2. Describe chemical change and chemical reaction with proper examples. Explain how to understand the nature of chemical changes with the help of an experiment.
Answer: A change in which one or more new substances with different properties are formed is known as chemical change. For example when vinegar is mixed with baking soda, the interaction produces a salt, a gas and water vapour. This is an example of a chemical change. The change is irreversible.
Rusting is a type of Chemical Change. It results in the formation of Iron Oxide which is an entirely new substance. Chemical Reaction of Rusting is as follows:
Iron + Oxygen (from environment) + Water (Humidity) —> Iron Oxide (Rust)
Q.3. (a) Can all changes be always reversed? Describe with examples.
(b) Describe the roles of heat and interaction between substances in chemical changes. Explain with proper examples.
Answer a) Some of the changes can be reversed The change of state like ice to water, water to steam and vice-versa can be reversed by reversing the condition. On heating, ice changes to water and water changes to steam. So, cooling will bring about the reverse process, i.e., change of water to ice or steam to water.
Some of the changes cannot be reversed. For example, if we cut a piece of paper to make a boat instead of folding it or in bursting of a tyre, we do not get back the original substance. Similarly, when we prepare a dough from flour and water, we do not get back the flour from the dough. The chapatti made from this dough by rolling it and baking it, will not give back the dough.
b) In a chemical change, a large amount of energy in the form of heat is involved. For example, during photosynthesis, energy of the sun is used by plants to prepare food. When a fuel is burnt, energy is given out in the form of heat and light. So, we see that energy may either be absorbed or given out during a chemical change.