Chapter 01 Matter in Our Surroundings Exercise
Exercises
1. Convert the following temperatures to the celsius scale.
(a) $293 K$
(b) $470 K$
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Answer
In order to covert temperature from Kelvin to Celsius scale, we have to subtract 273 from the given value because $K-273={ }^{\circ} C$
(a) $293 K-273=20^{\circ} C$
(b) $470 K-273=197^{\circ} C$
2. Convert the following temperatures to the kelvin scale.
(a) $25^{\circ} C$
(b) $373^{\circ} C$
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Answer
To convert temperature from Celsius to Kelvin scale, add 273 to the given values because ${ }^{\circ} C+273=K$
(a) $25^{\circ} C+273=298 K$
(b) $373^{\circ} C+273=646 K$
3. Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.
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Answer
(a) Naphthalene is a substance which directly changes from solid to gas on heating by the process of sublimation. So, the naphthalene balls disappear with time as they sublime due to heat of surroundings.
(b) The smell (aroma) of perfume reaches several meters away due to the fast diffusion of the gaseous perfume particles through the air.
4. Arrange the following substances in increasing order of forces of attraction between the particles - water, sugar, oxygen.
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Answer
The forces of attraction are strongest in solids and weakest (or negligible) in case of gases. Sugar is a solid, water is in liquid form and oxygen is a gas so, the order of forces of attraction is oxygen $<$ water $<$ sugar.
5. What is the physical state of water at-
(a) $25^{\circ} C$
(b) $0^{\circ} C$
(c) $100^{\circ} C$ ?
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Answer
At zero ${ }^{\circ} C$ temperature water (liquid) get starts to convert into its solid form (ice) and at $100^{\circ} C$ temperature water (liquid) starts to change into water vapours. Between $0^{\circ}$ to $100^{\circ} C$ it remains in liquid state.
Thus,
(a) Liquid state
(b) Solid or/and liquid state (Transition state)
(c) Liquid or/and gaseous state (Transition state)
6. Give two reasons to justify-
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.
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Answer
(a) Water is a liquid at room temperature because
It has a tendency to flow.
It takes the shape of the container in which it is filled, but its volume remains the same.
(b) An iron almirah is a solid at room temperature because
Its shape and volume are definite.
It is hard and rigid.
Its density is high.
7. Why is ice at $273 K$ more effective in cooling than water at the same temperature?
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Answer
Ice at 273K has less energy than water (although both at the same temperature). Water is having additional latent heat of fusion, hence at $273 K$ ice is more effective cooling than water
8. What produces more severe burns, boiling water or steam?
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Answer
Steam causes more severe burns than boiling water. The reason is that it releases the extra amount of heat (latent heat) which it has already taken during vaporization
9. Name A,B,C,D,E and $F$ in the following diagram showing change in its state
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Answer
$A=$ Melting or fusion, where solid changes into liquid.
$B=$ Evaporation or vaporization, where liquid changes into gas.
$C=$ Condensation or liquification where gas changes into liquid.
$D=$ Freezing or solidification, where liquid changes into solid.
$E=$ Sublimation, where solid directly changes into gas without coming in liquid state.
$F=$ Sublimation, where gas changes into solid without coming to liquid state.
