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Evaporation - class-IX

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Rate of evaporation increases 

  1. with the rise in temperature

  2. with the fall in temperature

  3. irrespective of temperature

  4. only beyond room temperature


Correct Option: A
Explanation:

Rate of evaporation Increases with the rise in temperature as increasing temperature increases the kinetic energy of molecules of the liquid which facilitates the molecule to convert into vapour.

Water evaporates under atmospheric pressure. Without changing the temperature, the same water is placed under partial vacuum. The rate of evaporation _________.

  1. increases

  2. drop to zero

  3. decreases

  4. remain unaffected


Correct Option: A
Explanation:
In partial pressure, the pressure is less;
According to Le-chatlier's principle on decreasing pressure; volume increases, so more water into gas(vapour)
So, rate of evaporation increases.

When the temperature of water rises, the rate of evaporation

  1. increases

  2. decreases

  3. remain the same

  4. first decrease then increases


Correct Option: A
Explanation:

The higher the temperature of the substance the greater the kinetic energy of the molecules at its surface and therefore the faster the rate of their evaporation.

One of the most common phenomenon related to rainfall is

  1. Evaporation

  2. Vaporization

  3. Fusion

  4. Solidification


Correct Option: A
Explanation:

Rainfall occurs primarily due to evaporation of water from water bodies like lakes and oceans and condensation of water in the form of precipitation like rainfall or snowfall.

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

  1. Temperature

  2. Humidity

  3. Exposed Surface Area

  4. All of the above


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

  1. Rapid

  2. Slow

  3. medium

  4. Neutral


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.

  1. True

  2. False


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 .

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

  1. Higher

  2. Lower

  3. Same

  4. None


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?

  1. It decreases gradually

  2. It increases

  3. Remains same

  4. It decreases rapidly


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?

  1. Pressure on evaporating substance

  2. Exposed surface area of the evaporating substance

  3. Shape of the evaporating substance

  4. Temperature


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?

  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.


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?

  1. Temperature

  2. Motion of air

  3. Nature of liquid

  4. Humidity of surrounding


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.

Choose the correct statements from the following

  1. Evaporation takes place from the surface of a liquid at all temperatures.

  2. The rate of evaporation depends upon the area of the exposed surface of the liquid, nature of the liquid and its temperature.

  3. The rate of evaporation depends on the pressure to which the liquid is subjected.

  4. The cooling produced in evaporation is a consequence of the fact that a liquid has latent heat.


Correct Option: A,B,C,D
Explanation:

Evaporation is a type of vaporization of a liquid that occurs from the surface of a liquid into a gaseous phase. So there is loss of energy due to latent heat of the liquid.

For molecules of a liquid to evaporate, they must be located near the surface, they have to be moving in the proper direction, and have sufficient kinetic energy to overcome liquid-phase inter-molecular forces. When only a small proportion of the molecules meet these criteria, the rate of evaporation is low. Since the kinetic energy of a molecule is proportional to its temperature, evaporation proceeds more quickly at higher temperatures and high surface area.
Evaporation happens faster if there is less exertion on the surface keeping the molecules from launching themselves.
So all the options are correct.

Water evaporates under atmospheric pressure. Without changing the temperature, the same water is placed in a partial vacuum. The rate of evaporation will

  1. increase

  2. drop to zero

  3. decrease

  4. remain unaffected


Correct Option: A
Explanation:
In partial vacuum, the pressure is very less.
According to Le-chatelier's principle on decreasing pressure, volume increases so more water converts into gas (vapour).

Soda bottles are made of thick glass so that they can withstand an increase in :

  1. pressure during summer

  2. temperature during summer

  3. viscosity

  4. potential energy


Correct Option: A
Explanation:
Gas, liquid and solid expand on heating.
Gas expands the max. due to free of gas molecules or almost zero force of attraction between them. On heating they gain K.E. and move up to any place. This gives expansion of gases.
The pressure of gas inside closed container increases upon heating. This is seen that soda bottle explodes in summer. So the air made up of thick glass so that they can withstand pressure.

A fan produces a feeling of comfort because:

  1. A fan supplies cool air

  2. Of the evaporation of sweat

  3. Fan increase the humidity in air

  4. Fan decrease the humidity in air


Correct Option: B
Explanation:

A fan produces a feeling of comfort because of evaporation of sweat because on hot day, our body sweats to loose heat through the evaporation of moisture.In still air evaporation is slow. A fan or breeze helps by replacing hot humid air with cooler dries air that allow for more evaporation


When the temperature of water rises, the rate of evaporation decreases. State whether true or false.

  1. True

  2. False


Correct Option: B
Explanation:
The statement if False.
Actually, rate of evaporation of a liquid decreases as the temperature decreases. As intermolecular force increase rate of evaporation decreases. This happens because intermolecular force make it less likely for the molecules on the surface to escape from liquid and become vapour gas. As temperature increases rate of evaporation increases.

Why mercury do not evaporate at room temperature?

  1. Because melting point of mercury is higher

  2. Because boiling point of mercury is higher

  3. Because boiling point of mercury is lower

  4. Because boiling point of mercury is equal to room temperature


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 temperature of the liquid is closer to its boiling point, greater is the evaporation. 
Besides the boiling point being higher, the cohesive force of attraction among the molecules of mercury is greater than other liquids like water. This further reduces the evaporation rate.

Evaporation is the process of changing liquid into vapour below its boiling point. State whether true or false.

  1. True

  2. False


Correct Option: A
Explanation:
Evaporation is the process of changing liquid into vapour below B.P. (boiling point)
It is the type of vaporisation that occurs on the surface of liquid due to increase in temperature or pressure it changes liquid into gaseous phase before reaching to B.P. The surrounding gas must not be saturated by evaporating substance.

A dog pants with its tongue sticking out on a hot day. Which of the following is the correct reason?

  1. It is its habit

  2. Producing more saliva cools down the body temperature.

  3. Saliva vapourises, cooling the tongue

  4. It is a genetic disease found in few animals like dogs.


Correct Option: C
Explanation:

Evaporation causes cooling.
A dog pants with its tongue sticking out on a hot day because its saliva vapourises, cooling the tongue.

Relative humidity is the percentage of the

  1. absolute humidity value to the amount of humidity actually present

  2. increase of humidity/absolute humidity

  3. amount of humidity actually present to the absolute humidity

  4. none of these


Correct Option: C
Explanation:

The ratio of actual amount of water vapour present in volume of air at a given temperature to maximum amount that air could hold at that temperature, expressed as percentage is relative humidity.

The molecules of liquid change into vapour when the pressure of molecules of liquid

  1. exceeds the atmospheric pressure

  2. becomes less than the atmospheric pressure

  3. becomes equal to the atmospheric pressure

  4. becomes zero


Correct Option: C
Explanation:

When the pressure of molecules of liquid become equal to the atmospheric pressure, the molecules of liquid change into vapours.

Water in an earthen pitcher gets cooled due to

  1. slower rate of evaporation

  2. faster rate of evaporation

  3. no evaporation at all

  4. some unknown reason


Correct Option: B
Explanation:

Earthen pots are used in summer. The pot has several pores through which water rinses out to the outer surface of the earthen pot and evaporates. In this process it takes away heat from the water inside the pitcher. As a result, the water inside gets cooled.

Drying up of clothes is fastest on a 

  1. hot day without winds

  2. cold day without winds

  3. hot,dry and windy day

  4. humid and windy day


Correct Option: C
Explanation:

Evaporation is the key process involved in the drying up of clothes. Since evaporation is fastest in dry weather on a windy day, clothes dry faster on these days.

Dogs hang out their tongue during summers to achieve cooling. Which phenomenon is involved in the process?

  1. Condensation

  2. Evaporation

  3. Vaporization

  4. Fusion


Correct Option: B
Explanation:

Dogs hang out their tongue during summers. This helps produce a cooling effect due to evaporation.

Salt is extracted from sea-water by

  1. Treating with chemicals depositing salt at the bottom

  2. Filtering the water by nets blocking the salt.

  3. Boiling the water by coil leaving behind the salt.

  4. Evaporating the water by sun leaving behind the salt.


Correct Option: D
Explanation:

Salt is produced by direct evaporation of sea-water in sun. This process is cheapest and most efficient.

From below what are used to prevent pesticides, fertilizers and salt from agricultural wastewater from contaminating the water bodies they flow into?

  1. Evaporation ponds

  2. Vaporising ponds

  3. Fermented ponds

  4. Wet ponds


Correct Option: A
Explanation:

Evaporation ponds are used. Evaporation ponds are artificial ponds with very large surface area that are designed to efficiently evaporate water by sunlight and exposure to the ambient temperature.

To produce salt from sea water, which phenomena is used

  1. Evaporation

  2. Vaporisation

  3. Fermentation

  4. Sublimation


Correct Option: A
Explanation:

Sea water is a mixture of water and salt , by the phenomenon of evaporisation water of this mixture is evaporated and we get salt only .

When we apply paint in our house, it dries out after some while. This happens due to what?

  1. Cooling

  2. Evaporation

  3. Fermentation

  4. None of these


Correct Option: B
Explanation:

The wet paint is dried out because liquid portion in paint is evaporated . Although evaporisation is also a type of vaporisation .


Splashes dry up at the edges of puddle due to what?

  1. Vaporisation

  2. Evaporation

  3. Sublimation

  4. Fermentation


Correct Option: B
Explanation:

Splashes dry up at the edges of puddle , because of evaporisation as high energy molecules of water escape from water .

When we dry our wet clothes in sun in a line then which phenomena applies to make them dry?

  1. Sublimation

  2. Fermentation

  3. Vaporisation

  4. Evaporation


Correct Option: D
Explanation:

Clothes are dried by evaporation due to heat from sunlight . In a line , clothes get sunlight for whole day , and due to heat from sun, rate of evaporation increases and clothes dry quickly .

In our daily chores when we mop our house floor then it becomes dry after some time. Which phenomena applies here?

  1. Fermentation

  2. Sublimation

  3. Vaporisation

  4. Evaporation


Correct Option: D
Explanation:

Our floor get wet due to mopping , and after some time water droplets are evaporated and floor become dry .


What is not true about evaporation?

  1. Greater the surface area of the liquid, the quicker is the evaporation

  2. Evaporation produces cooling

  3. Evaporation takes place at all the temperatures

  4. Evaporation is nothing but boiling at the highest temperature of the liquid


Correct Option: D
Explanation:

Evaporization is the vaporization process of converting the liquid phase to vapour phase when surrounding temperature is more than liquid / water temperature.

It should not be confused with boiling as boiling means whole phase change from liquid to vapour at highest temperature.

Statement-1
Evaporation takes place from the surface of a liquid.
Statement-2
The molecules at the surface have less attractive energy than those inside the liquid.

  1. Statement-1 is true, Statement-2 is true and Statement-2 is the correct explanation for Statement- 1

  2. Statement-1 is true, Statement-2 is true but Statement-2 is not the correct explanation for Staement-1

  3. Statement-1 is true, Statement-2 is false.

  4. Statement-1 is false, Statement-2 is true.


Correct Option: A
Explanation:

Evaporation is a surface phenomenon.
Particles present on the surface of a liquid only face attraction from one side (the side containing fluid particles) and surface tension. Where as particles inside the liquid would face attractive forces from all around, making it difficult for such particles to evaporate or escape.
Hence the statement is true, explanation is true and the explanation is the correct explanation for the statement.

Which of the following statement is wrong ?

  1. At room temperature evaporation of water is rapid as compared to ethanol

  2. Water is more viscous as compared to ethanol

  3. Liquid drops are spherical in shape

  4. Clothes are easily dried in dry day as compared to humid days


Correct Option: A,B
Explanation:

A: At room temperature evaporation of ethanol is rapid as compared to water. Hence, A is incorrect. 

B: water is more viscous compared to ethanol, hence statement is true. 
C: liquid drops are spherical due to surface tension of liquid drop,hence statement is true.
D: Clothes are dried easily as it is less humid on dry day,hence statement is true

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