Q1Written answer
Convert the following temperature to Celsius scale.
(a) 293K (b) 470K
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Worked solution
0°C=273K
(a) 293K= (293 – 273)°C = 20°C
(b) 470K= (470 – 273)°C = 197°C
NCERT · Class 9 · Science
Chapter 1: Matter in Our Surroundings
Practice each question, then open the answer or worked solution.
Chapter Exercise –
Textbook page 12 · 9 questionsQ2Written answer
Convert the following temperatures to the Kelvin scale.
(a) 25°C (b) 373°C
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Worked solution
0°C = 273K
(a) 25°C = (25+273)K = 298K
(b) 373°C = (373+273)K = 646K
Q3Written answer
Give reason for the following observations:
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume while sitting several metres away.
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Worked solution
(a) At room temperature, naphthalene balls undergo sublimation wherein they directly get converted from a solid to a gaseous state without having to undergo the intermediate state, i.e., the liquid state.
(b) Molecules of air move at a higher speed and have large intermolecular spaces. Perfumes comprise substances that are volatile, which scatter quickly in air, becoming less concentrated over a distance. Hence, we are able to smell perfume sitting several metres away.
Q4Written answer
Arrange the following in increasing order of forces of attraction between the particles – water, sugar, oxygen.
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Worked solution
Oxygen (gas) < water (liquid) < sugar (solid)
Q5Written answer
What is the physical state of water at –
(a) 25°C (b) 0°C (c) 100°C?
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Worked solution
(a) At 25°C, the water will be in liquid form (normal room temperature)
(b) At 0°C, the water is at its freezing point, hence both solid and liquid phases are observed.
(c) At 100°C, the water is at its boiling point, hence both liquid and gaseous states of water (water vapour) are observed.
Q6Written answer
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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Worked solution
(a) Water persists as a liquid at room temperature since its melting point is lower than room temperature and its boiling point (100o C) is higher.
Similarly,
(i). A fixed volume is occupied by a fixed mass of water.
(ii). At room temperature, water does not have a fixed shape and flows to fit the container’s shape.
As a result, water is a liquid at room temperature.
(b) Because its melting and boiling points are above room temperature, an iron almirah is a solid at room temperature. In the same way,
(i) An iron almirah is rigid and has a predetermined shape.
(ii) Metals have a relatively high density.
As a result, at room temperature, iron almirah is a solid.
Q7Written answer
Why is ice at 273K more effective in cooling than water at the same temperature?
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Worked solution
At 273 K, ice will absorb heat energy or latent heat from the medium to overcome fusion and transform into water. As a result, ice has a greater cooling impact than water at the same temperature since water does not absorb the excess heat from the medium.
Q8Written answer
What produces more severe burns, boiling water or steam?
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Worked solution
Steam produces severe burns. It is because it is an exothermic reaction that releases a high amount of heat which it had consumed during vaporization.
Q9Written answer
Name A, B, C, D, E and F in the following diagram showing a change in its state.
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Worked solution
Interconversion of three states of matter: Using temperature or pressure, any state of matter can be turned into another.
(A) Solid to Liquid → Melting (or) fusion (or) liquefaction
(B) Liquid to Gas → Evaporation (or) vaporization
(C) Gas to liquid → Condensation
(D) Liquid to Solid → Solidification
(E) Solid to Gas → Sublimation
(F) Gas to Solid → solidification