Tag: heat, internal energy and work

Questions Related to heat, internal energy and work

From the following which are the factors affecting the rate of evaporation?

physics the kinetic model of matter evaporation heat, internal energy and work phase change

  1. Temperature

  2. Humidity

  3. Exposed Surface Area

  4. All of the above

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Correct Option: D
Explanation:

1. Temperature - If we increase the temperature of a liquid, its molecules get more kinetic energy and more molecules will come out rapidly from the surface of liquid i.e. rate of evaporation increases.


2. Humidity - Humidity is measurement of amount of vapour present in air. If humidity is high, it will be difficult for liquid to add more vapour in air as there is already high amount of vapour, therefore with increase in humidity, rate of evaporation decreases and vice- versa.


3. Exposed surface area - If exposed surface area is increased, more liquid molecules come on the surface, as evaporation is a surface process, therefore rate of evaporation increases.

Hence, all these factors affect the rate of evaporation.

Evaporation is which type of process

physics the kinetic model of matter evaporation heat, internal energy and work phase change

  1. Rapid

  2. Slow

  3. medium

  4. Neutral

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Correct Option: B
Explanation:

Evaporation and boiling, both are vaporisation. Boiling is a rapid process, which happens in the whole liquid whereas evaporation happens only on the surface of liquid and is a slow process.

State True or False :
The larger the exposed surface area, lower is the rate of evaporation.

physics the kinetic model of matter evaporation heat, internal energy and work phase change

  1. True

  2. False

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Correct Option: B
Explanation:

Larger surface area means more molecules per unit volume in the exposed surface area , which are capable to go out from surface i.e. larger rate of evaporation . Hence given statement is false .

State True and False :
If humidity is high in the atmosphere, rate of evaporation is higher. 

physics the kinetic model of matter evaporation heat, internal energy and work phase change

  1. True

  2. False

Show answer
Correct Option: B
Explanation:
If the humidity is high in the atmosphere, the rate of evaporation is lower as the air is full of water vapour and not able to take more of humidity. Thus, evaporation process becomes slower.

State True or False :
Evaporation takes place at all temperatures.

physics the kinetic model of matter evaporation heat, internal energy and work phase change

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

True, Evaporation takes place at any temperature. When the air molecule strike the surface, they are going to impart some energy to water molecules. If this energy is sufficient enough to change the phase of water molecules; we experience a phenomenon evaporation. It can occur at any temperature.

If the temperature is high then what is the rate of evaporation?

physics the kinetic model of matter evaporation heat, internal energy and work phase change

  1. Higher

  2. Lower

  3. Same

  4. None

Show answer
Correct Option: A
Explanation:

If temperature is high then kinetic energy of the molecules will be high and rate of evaporation is higher.

What happens to the rate of evaporation when there is more exposed surface area of liquid?

physics the kinetic model of matter evaporation heat, internal energy and work phase change

  1. It decreases gradually

  2. It increases

  3. Remains same

  4. It decreases rapidly

Show answer
Correct Option: B
Explanation:

Evaporation is a process in which some molecules of a liquid, which have greater kinetic energy, escape from the liquid and enter the atmosphere.

When the surface area exposed is more, the molecules get greater opportunity to escape. Hence more molecules escape and rate of evaporation increases.

Which of the following does not affect the rate of evaporation?

physics the kinetic model of matter evaporation heat, internal energy and work phase change

  1. Pressure on evaporating substance

  2. Exposed surface area of the evaporating substance

  3. Shape of the evaporating substance

  4. Temperature

Show answer
Correct Option: C
Explanation:

Evaporation is a process in which some molecules of a liquid, which have greater kinetic energy, escape from the liquid and enter the atmosphere.

If pressure is greater, the molecules need greater energy to overcome the pressure and hence evaporation decreases with increase in pressure.
Due to more surface area, more molecules get a chance to escape, hence faster is the evaporation.
At higher temperature, molecules have greater kinetic energy, hence can easily escape the liquid.
But shape of the surface of the liquid doesn't affect evaporation.

Why skin feels dry in an air-conditioned room?

physics the kinetic model of matter evaporation heat, internal energy and work phase change

  1. Because the rate of evaporation decreases with lower humidity.

  2. Because the rate of evaporation increases with lower humidity.

  3. Because the rate of evaporation remains same with lower humidity.

  4. Because the rate of evaporation increases with higher humidity.

Show answer
Correct Option: B
Explanation:

Evaporation is a process in which some molecules of a liquid, which have greater kinetic energy, escape from the liquid and enter the atmosphere.

When the humidity is lower, the air's capacity to absorb vapour is greater. The adhesive force of attraction between liquid molecules increases and more molecules escape into the atmosphere. Hence evaporation is greater in dry air.

The moving air from the hair dryer removes the molecules of liquids as soon as they escape from the surface of your  hair.
Which factor of evaporation is responsible for the above example?

physics the kinetic model of matter evaporation heat, internal energy and work phase change

  1. Temperature

  2. Motion of air

  3. Nature of liquid

  4. Humidity of surrounding

Show answer
Correct Option: B
Explanation:

Evaporation is a process in which some molecules of a liquid, which have greater kinetic energy, escape from the liquid and enter the atmosphere.

Evaporation occurs faster at a higher temperature.
The wind of the hairdryer being hotter than room temperature, speeds up the evaporation process.