Question 1: Convert the following temperatures to the Celsius scale.
(a) 300 K (b) 573 K
Answer:
Using the formula: – T (°C) = T (K) – 273.15
300K = (300 – 273) = 27O C
573 K = (573 – 273) = 300O C
Question 2: Convert the following temperatures to the Kelvin scale.
(a) 25°C (b) 373°C
Answer:
Using the formula: – T (°C) = T (K) – 273.15
Kelvin is the SI unit of temperature, where 0O C =273.16K (approx. 273K)
25o C = (25 + 273) = 298K
373o C = ( 373 + 273) = 646K
Question 3: Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
Answer:
Naphthalene balls disappear with time without leaving any solid, because naphthalene balls exhibit the property of sublimation. This means that, it changes from solid state to gas directly.
(b) We can get the smell of perfume sitting several metres away.
We can get the smell of perfume sitting several metres away because perfume contains volatile solvent which vaporises in no time and diffuses faster into the air.
Question 4: Arrange the following substances in increasing order of forces of attraction between the particles— water, sugar, oxygen.
Answer:
Since sugar is a solid therefore the force of attraction between the particles is very strong.
Water is a liquid therefore the force of attraction are weaker as compared to the solid that is sugar.
Oxygen is a gas therefore the force of attraction between the particles is weakest.
Thus, we can write the increasing order of attraction between the particles as:
Oxygen< Water < Sugar
Question 5: What is the physical state of water at —?
(a) 25°C (b) 0°C (c) 100°C
Answer:
Water at 25o C will be in the liquid state (normal room temperature)
At 0o C water is at its freezing point hence can exist as both solid and liquid.
At 100o C the water is at its boiling point therefore, can exist as both liquid and vapour.
Question 6: Give two reasons to justify—
(a) Water at room temperature is a liquid.
Answer:
Water at room temperature in its liquid state thereby exhibits all properties of a liquid, like it flows at this temperature and it has a definite volume and takes the shape of the container.
(b) An iron Almirah is a solid at room temperature.
An iron Almirah is a solid at room temperature because the melting point of iron is extremely high and room temperature is only about 20- 25o C therefore it is a solid at room temperature.
Question 7: Why is ice at 273 K more effective in cooling than water at the same temperature?
Answer:
Ice at 273K has less energy than water even though both are at the same temperature.
Water possesses the additional latent heat of fusion at the same temperature in the form of extra energy. That is why ice is more effective.
Question 8: What produces more severe burns, boiling water or steam?
Answer: Steam produces more severe burns than boiling water, this is because steam has more energy than boiling water, in the form of latent heat of vaporization.
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