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physics Physics For High Schools (KS4)

Solved problems for the chapter:

Evaporation

The chapter does not contain theoretical materials.

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Detailed solution steps are available at:

https://en.openprof.com/wb/chapter:evaporation/3525/

Example 1.

A student measures the mass of warm water in an open container over four minutes. The container is kept at a constant temperature. The results are in the table below:

Time (min)	0.0	1.0	2.0	3.0	4.0
Mass (g)	35.7	32.4	27.2	25.0	20.5

Why does the mass of the water change?

The water evaporates.
The water freezes.
The water condenses.
The water boils.

Example 2.

Ether is a liquid that evaporates easily at room temperature. The rate at which ether evaporates can be increased by bubbling air through it. The diagram below shows this process.

Which of the following statements is/are true as air is bubbled through the ether?

The temperature of the ether is decreased.
The surface area of the ether is increased.
That evaporated molecules of the ether are removed at a greater rate.

A beaker contains hot liquid. Some of the liquid evaporates. What happens to the mass and what happens to the weight of the liquid in the cup?

	mass	weight
A	decreases	decreases
B	decreases	stays the same
C	stays the same	decreases
D	stays the same	stays the same

Which of the statements below are correct about the evaporation of a liquid?

Evaporation occurs at any temperature.
Evaporation only occurs at the boiling point.
Evaporation occurs where the liquid touches the bottom of the container.
Evaporation occurs at the surface of the liquid.
It is the higher energy molecules which escape.
The molecules gain energy as they escape.
The liquid temperature always rises when evaporation occurs.
Rapid evaporation produces cooling.

I, II, and IV
II, III, VI and VII
I, IV, V and VIII
I, III, V and VI

When water evaporates, some molecules escape. Which molecules escape?

the molecules at the bottom of the liquid with less energy than others.
the molecules at the bottom of the liquid with more energy than others.
the molecules at the surface with less energy than others.
the molecules at the surface with more energy than others.

A liquid is left in an open dish. After several days there is less liquid in the dish. Which statement explains this?

the least energetic molecules leave the surface and escape into the air
the least energetic molecules leave the surface and return
the most energetic molecules leave the surface and escape into the air
the most energetic molecules leave the surface and return

In an experiment, some part of a substance changes from a liquid to a gas. The temperature of the remaining liquid changes because of this. What is the name for this change of state and how does the temperature change?

	change of state	how temperature changes
A	condensation	decreases
B	condensation	increases
C	evaporation	decreases
D	evaporation	increases

During evaporation of a liquid, the more energetic molecules escape. The temperature of the remaining liquid changes. Which row identifies where these molecules escape from and describes the temperature change?

	molecules escape from the	temperature of remaining liquid
A	body of the liquid	decreases
B	body of the liquid	increases
C	surface of the liquid	decreases
D	surface of the liquid	increases

Evaporation occurs when molecules escapes from the liquid surface to the air above it. During this process the temperature of the liquid falls. Why does the temperature of the liquid fall?

The molecules in the vapor expand because the pressure is less
The molecules left in the liquid have more space to move around
The molecules move more slowly when they escape into the air
The molecules with the highest energies escape into the air

10.

Which statement about evaporation is correct?

Evaporation causes the temperature of the remaining liquid to decrease.
Evaporation does not occur from a cold liquid near its freezing point.
Evaporation does not occur from a dense liquid, such as mercury.
Evaporation occurs from all parts of a liquid.

11.

On a warm day, a carton of fresh milk is covered with a wet cloth. Why does this help to reduce the temperature of the milk?

Some water evaporates from the cloth so the remaining water becomes cooler.
The water has a very high thermal capacity.
The water insulates the milk from the warm air around it.
Water is always colder than the air around it.

12.

The diagram shows the more energetic water molecules escaping from the surface of liquid water.

What is this process called?

Brownian motion
condensation
evaporation
conduction

13.

Wet clothes are put out on a line to allow the water in the clothes to evaporate. Which type of weather would cause the water to evaporate most quickly?

a cold day with no wind
a cold day with wind
a hot day with no wind
a hot day with wind

14.

Which row correctly describes a liquid that is boiling?

	bubbles seen	where it takes place in the liquid
A	no	surface only
B	no	throughout liquid
C	yes	surface only
D	yes	throughout liquid

15.

What happens when the temperature of a liquid increases?

The mass of the liquid increases, making the liquid less dense.
The mass of the liquid increases, making the liquid more dense.
The volume of the liquid increases, making the liquid less dense.
The volume of the liquid increases, making the liquid more dense

16.

Which of these is true about the evaporation of a liquid?

The rate of evaporation is directly proportional to the temperature of the liquid.
The rate of evaporation is inversely proportional to the temperature of the liquid.
The rate of evaporation is independent of the temperature of the liquid.
The rate of evaporation is directly proportional to the humidity of the surrounding air.