Question

Q.1) Classify the following as physical or chemical change. Give a reason for your answer.
i) Respiration in living organisms.
ii) Making butter from cream
iii) Photosynthesis in green plant.
iv) Burning of phosphorous in air
v) Burning of wax candle.

Q.2) Give one example of chemical reaction in which
i) Heat is evolved.
ii) Light is evolved
iii) Light is absorbed
iv) Sound is produced

Q.3) Differentiate between:
i) Physical and chemical change
ii) Melting and boiling
iii) Sublimation and deposition
iv) Gas and vapour

Q.4) Give reason.
i) A liquid is that state of matter which has a definite mass and volume but no definite shape.
ii) Gases have no free surfaces.
iii) Burning of wax candle is both – a physical and chemical change.
iv) When magnesium is added to an acid, the test tube becomes hot.
v) When red lead is heated it turns yellow.

Q.5) Kinetic molecular theory explains interconversion of the states of matter. Justify?

Q.6) Magnesium ribbon bums in air and changes to white substance, i.e. magnesium oxide. When magnesium oxide dissolves in water, what type of change take place? Give reason in support of your answer. Express the change in the form of equation.
Q.7) Which type of change takes place in the following and state whether the energy is evolved or absorbed during the change?
Burning of a candle, lightning of a bulb, preparation of food by green plants, volcanic eruption, evaporation of petrol, burning of LPG.
Q.8) Give two examples for each of the following cases:
(a) Physical changes which are reversible.
(b) Physical changes which are not reversible.

Q.9) Describe two changes that are harmful. Explain why you consider them harmful? How can you prevent them?
Q.10) Rahul was a student of Class VII. His father purchased a new bicycle for him on his birthday. After few months, he found that the cycle chain and even the handle gets rusted. His father advised him to apply a coating of paint to the cycle and not to keep it in the open in future.
Now, answer the following questions:
(a) Why his cycle gets rusted?
(b) What do you mean by rusting of iron?
(c) What values are shown by Rahul’s father? [Value Based Question]

Q.11) Define interconversion of states of matter. What are the two factors responsible for the change of states of matter?

Q.12) Explain the factors affecting on Brownian motion.

Answer 1

Answer:

Q1

1. Chemical change as we take in new cells when we breathe again and again.

2. Chemical change as we cannot get back cream after making butter.

3. Chemical change.

4. Burning of wax candle is a chemical change as after burning of wax we cannot get it back in form of candle.

Explanation:

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