Question

5. Assign reasons for the following:-
a. Butter is generally wrapped in a wet cloth during summer if no refrigerator is available.

b. The latent heat of vaporization of steam is more than that of boiling water.

c. Melting of wax is a physical change.

d. Wet clothes do not dry easily on a rainy day.

e. Ice at 0°C appears colder in the mouth than water at 0°C.

Note :- Please give the answer with explanations. ​

Answer 1

A)Butter is generally wrapped in a wet cloth during summer if no refrigerator is available.

• Butter is generally wrapped in wet cloth during summer if no refrigerator is available.
• Evaporation takes place and heat is taken from the water and cooling after evaporation takes place and thus helps in keeping the butter cool and in shape without melting.

The latent heat of vaporization of steam is more than that of boiling water.

• Steam has more energy than boiling water. It possesses the additional latent heat of vaporization. So, when steam falls on skin and condenses to produce water it gives out 22.5 x 105 J/kg more heat than boiling water at the same temperature.

Melting of wax is a physical change.

• No new substances are formed. In a burning candle, there are both physical and chemical changes.
• The melting of the solid wax to form liquid wax and the evaporation of liquid wax to form wax vapour are physical changes. The burning of the wax vapour is a chemical change.

Why do wet clothes not dry easily on rainy days?

• During rainy days, when the temperature is low and the relative humidity is high, evaporation of water is slow, so wet clothes don't dry easily on rainy days.

Ice at 0°C appears colder in the mouth than water at 0°C.

• In your mouth, ice absorbs latent heat as well as the heat energy in order to attain your body temperature whereas Water at 0°C absorbs only heat energy to attain your body temperature. Thus water absorbs less heat energy from your body compared to ice. That's why ice feels colder.

Answer 2

Answer:

Explanation:

a.)In summer, the weather is a quite hot. As a result, water present in wet cloth readily evaporates. Since cooling is caused during evaporation, the temperature of butter gets lowered. This checks the rancidity of butter or it does not give any foul odour.

b.)When boiling water changes into steam, it absorbs a certain amount of heat energy. This shows that the latent heat of vaporisation of steam is more than that of boiling water.

c.)No new substance is formed and there is no change in the chemical properties of wax as a result of melting

d.)During rainy days, when the temperature is low and the relative humidity is high, evaporation of water is slow, so wet clothes don't dry easily on rainy days

e.)The latent heat absorbed by ice to get converted into water is greater than the heat absorbed by water at same temperature. Generally, ice has to absorb 3.3J/Kg to get converted into water. Thus water has more heat than ice.

Thus ice appears colder than water at 0°C

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