What happens when a liquid cools. When water freezes, it expands or contracts: simple physics

17.04.2024

We are surrounded by water, by itself, as part of other substances and bodies. It can be in solid, liquid or gaseous form, but water is always around us. Why does asphalt crack on the roads, why does a glass jar of water burst in the cold, why do windows fog up in the cold season, why does an airplane leave a white trail in the sky - we will look for answers to all these and other “whys” in this lesson. We will learn how the properties of water change when heated, cooled and frozen, how underground caves and bizarre figures in them are formed, how a thermometer works.

Topic: Inanimate nature

Lesson: Properties of liquid water

In its pure form, water has no taste, smell or color, but it is almost never like that, because it actively dissolves most substances in itself and combines with their particles. Water can also penetrate into various bodies (scientists have found water even in stones).

If you fill a glass with tap water, it will appear clean. But in fact, it is a solution of many substances, among which there are gases (oxygen, argon, nitrogen, carbon dioxide), various impurities contained in the air, dissolved salts from the soil, iron from water pipes, tiny undissolved dust particles, etc.

If you pipette drops of tap water onto clean glass and let it evaporate, barely visible spots will remain.

The water of rivers and streams, and most lakes contains various impurities, for example, dissolved salts. But there are few of them, because this water is fresh.

Water flows on the ground and underground, fills streams, lakes, rivers, seas and oceans, creating underground palaces.

Making its way through easily soluble substances, water penetrates deep underground, taking them with it, and through slits and cracks in rocks, forming underground caves, dripping from their roofs, creating bizarre sculptures. Billions of water droplets evaporate over hundreds of years, and substances dissolved in water (salts, limestones) settle on the cave arches, forming stone icicles called stalactites.

Similar formations on the floor of a cave are called stalagmites.

And when a stalactite and stalagmite grow together to form a stone column, it is called a stalagnate.

Observing ice drift on a river, we see water in a solid (ice and snow), liquid (flowing underneath) and gaseous state (tiny particles of water rising into the air, which are also called water vapor).

Water can be in all three states at the same time: there is always water vapor in the air and clouds, which consist of water droplets and ice crystals.

Water vapor is invisible, but it can be easily detected if you leave a glass of water chilled in the refrigerator for an hour in a warm room, droplets of water will immediately appear on the walls of the glass. Upon contact with the cold walls of the glass, the water vapor contained in the air is converted into water droplets and settles on the surface of the glass.

Rice. 11. Condensation on the walls of a cold glass ()

For the same reason, the inside of the window glass fogs up during the cold season. Cold air cannot contain as much water vapor as warm air, so some of it condenses - turns into water droplets.

The white trail behind a plane flying in the sky is also the result of water condensation.

If you bring a mirror to your lips and exhale, tiny droplets of water will remain on its surface, this proves that when breathing a person inhales water vapor with the air.

When water is heated, it “expands.” This can be proven by a simple experiment: a glass tube was lowered into a flask of water and the water level in it was measured; then the flask was lowered into a vessel with warm water and, after heating the water, the level in the tube was re-measured, which rose noticeably, since water increases in volume when heated.

Rice. 14. A flask with a tube, the number 1 and a line indicates the initial water level

Rice. 15. A flask with a tube, the number 2 and a line indicates the water level when heated

As water cools, it “compresses.” This can be proven by a similar experiment: in this case, a flask with a tube was lowered into a vessel with ice; after cooling, the water level in the tube decreased relative to the original mark, because the water decreased in volume.

Rice. 16. A flask with a tube, the number 3 and a line indicates the water level during cooling

This happens because water particles, molecules, move faster when heated, collide with each other, are repelled from the walls of the vessel, the distance between the molecules increases, and therefore the liquid occupies a larger volume. When water cools, the movement of its particles slows down, the distance between molecules decreases, and the liquid requires less volume.

Rice. 17. Water molecules at normal temperature

Rice. 18. Water molecules when heated

Rice. 19. Water molecules during cooling

Not only water, but also other liquids (alcohol, mercury, gasoline, kerosene) have such properties.

Knowledge of this property of liquids led to the invention of a thermometer (thermometer) that uses alcohol or mercury.

When water freezes, it expands. This can be proven if a container filled to the brim with water is loosely covered with a lid and placed in the freezer; after a while we will see that the formed ice will lift the lid, going beyond the container.

This property is taken into account when laying water pipes, which must be insulated so that when freezing, the ice formed from the water does not rupture the pipes.

In nature, freezing water can destroy mountains: if water accumulates in rock cracks in the fall, it freezes in winter, and under the pressure of ice, which occupies a larger volume than the water from which it was formed, rocks crack and collapse.

Water freezing in the cracks of roads leads to the destruction of asphalt pavement.

Long ridges resembling folds on tree trunks are wounds from wood ruptures under the pressure of tree sap freezing in it. Therefore, in cold winters you can hear the cracking of trees in a park or forest.

Vakhrushev A.A., Danilov D.D. The world around us 3. M.: Ballas.
Dmitrieva N.Ya., Kazakov A.N. The world around us 3. M.: Fedorov Publishing House.
Pleshakov A.A. The world around us 3. M.: Education.

Festival of Pedagogical Ideas ().
Science and education ().
Public class ().

Make a short test (4 questions with three answer options) on the topic “Water around us.”
Conduct a small experiment: place a glass of very cold water on a table in a warm room. Describe what will happen, explain why.
*Draw the movement of water molecules in a heated, normal and cooled state. If necessary, write captions on your drawing.

Topic: Inanimate nature

Lesson: Properties of liquid water

If you pipette drops of tap water onto clean glass and let it evaporate, barely visible spots will remain.

The water of rivers and streams, and most lakes contains various impurities, for example, dissolved salts. But there are few of them, because this water is fresh.

Water flows on the ground and underground, fills streams, lakes, rivers, seas and oceans, creating underground palaces.

Similar formations on the floor of a cave are called stalagmites.

And when a stalactite and stalagmite grow together to form a stone column, it is called a stalagnate.

Observing ice drift on a river, we see water in a solid (ice and snow), liquid (flowing underneath) and gaseous state (tiny particles of water rising into the air, which are also called water vapor).

Water can be in all three states at the same time: there is always water vapor in the air and clouds, which consist of water droplets and ice crystals.

Rice. 11. Condensation on the walls of a cold glass ()

For the same reason, the inside of the window glass fogs up during the cold season. Cold air cannot contain as much water vapor as warm air, so some of it condenses - turns into water droplets.

The white trail behind a plane flying in the sky is also the result of water condensation.

If you bring a mirror to your lips and exhale, tiny droplets of water will remain on its surface, this proves that when breathing a person inhales water vapor with the air.

Rice. 14. A flask with a tube, the number 1 and a line indicates the initial water level

Rice. 15. A flask with a tube, the number 2 and a line indicates the water level when heated

Rice. 16. A flask with a tube, the number 3 and a line indicates the water level during cooling

Rice. 17. Water molecules at normal temperature

Rice. 18. Water molecules when heated

Rice. 19. Water molecules during cooling

Not only water, but also other liquids (alcohol, mercury, gasoline, kerosene) have such properties.

Knowledge of this property of liquids led to the invention of a thermometer (thermometer) that uses alcohol or mercury.

This property is taken into account when laying water pipes, which must be insulated so that when freezing, the ice formed from the water does not rupture the pipes.

Water freezing in the cracks of roads leads to the destruction of asphalt pavement.

Vakhrushev A.A., Danilov D.D. The world around us 3. M.: Ballas.
Dmitrieva N.Ya., Kazakov A.N. The world around us 3. M.: Fedorov Publishing House.
Pleshakov A.A. The world around us 3. M.: Education.

Festival of Pedagogical Ideas ().
Science and education ().
Public class ().

Make a short test (4 questions with three answer options) on the topic “Water around us.”
Conduct a small experiment: place a glass of very cold water on a table in a warm room. Describe what will happen, explain why.
*Draw the movement of water molecules in a heated, normal and cooled state. If necessary, write captions on your drawing.

Class: 5

Lesson objectives:

expand knowledge about water, its properties, the meaning of water, introduce the concepts of solution, suspension, the meaning of solutions in nature and human life;
develop observation, mental activity, cultivate a caring attitude towards water.

Equipment:

chemical glassware for experiments,
alcohol lamp,
substances for experiments,
costumes for droplets, to
cards for independent work.

During the classes

Hello guys! Today our lesson is dedicated to water and is called “Her Majesty – Water”. During the lesson we will expand our knowledge about water, get acquainted with its properties, as well as water as a solvent of substances. Let's find out what a solution is and what a suspension is.

We open the notebooks in which we write down the topic of the lesson “Her Majesty is Water.”

Every person uses water for cooking and other domestic needs, for industrial enterprises, for growing plants and animals. The droplets will tell us what water is.

Drop 1: Water is a familiar and unusual substance. Scientists are absolutely right: there is no substance on Earth more important for us than ordinary water. Almost three quarters of the surface of our planet is occupied by seas and oceans. Solid water - snow and ice - covers 20% of the land. The climate of our planet depends on water. The earth would have cooled long ago and turned into lifeless stone if not for the water. When water heats up, it absorbs heat, and when it cools, it releases it. The water that is dispersed in the atmosphere – in the clouds in the form of steam – protects the Earth from cosmic cold.

Drop 2: Water has many amazing properties that make it unlike all other substances. But among them there is one unusual thing - this is her immortality. Approximately one billion tons of water is consumed by humanity per day. But the total amount of water does not decrease. As much as there was millions of years ago, there is as much in our time.

Drop 3: The role of water in life on Earth is great. Living organisms on our planet have adapted to all kinds of conditions: complete darkness, heat and cold. But no living creature can survive without water. All plants and animals contain water, and our own body is three-quarters water. Did you know that when a person loses 1 liter of water (this is approximately 2% of body weight), a feeling of thirst appears. When 6-8% of moisture is lost, a person falls into a semi-fainting state. Losing 10% of water causes hallucinations. And with a loss of more than 12%, people die.

Teacher: So what is water? (Children's answers) Water is a chemical substance that has its own properties. In notebooks we write down: Properties of water.

You are already familiar with some properties of water. Let's remember them, and our textbook will help us with this (working with a textbook).

Properties of water:

transparent;
colorless;
tasteless and odorless;
fluid;
can be in three states of aggregation;
can move from one state of aggregation to another.

(The properties of water are written down in a notebook)

Now let's get acquainted with some more of its properties. Experiments will help us with this.

Equipment:

2 flasks with a gas outlet tube,
2 crystallizers.

Substances:

water,
hot water,

Let's see what happens if we take two identical flasks with water and mark the water level with a mark. Place one in ice and the other in hot water. What's happening?

We observe that in hot water, the water in the flask rises above the mark, and in the flask, which is lowered into ice, on the contrary, it falls.

We conclude that water expands when heated and contracts when cooled.

Let's see another experience.

EXPERIENCE 2:

(The experience is demonstrated by the student as completed homework)

Equipment:

glass bottle with stopper.

Substance:

Student: I took a glass bottle, filled it with water, capped it tightly and took it out into the cold. When the water froze, the bottle burst and broke into pieces. This happened because water expands when it freezes.

Once, scientists conducted an experiment similar to this, but instead of a bottle, they took a cast-iron ball, filled it with water, screwed in the holes and placed it in severe frost. The water, freezing, tore the ball apart. So great is the power of expanding water.

Teacher: Guys, after demonstrating the experiments, what conclusion can be drawn? What properties, along with those that we have written down, does water have? (Children's answers)

Let's write down the properties of water in our notebooks:

water expands when heated;
Water contracts when cooled;
Water expands when it freezes.

It's time to consolidate the knowledge gained in our lesson. Please answer me the following questions:

If you pour water into a kettle or pan to the brim and start heating it, then after a while the water begins to splash out over the edge. Why is this happening? (Water expands when heated)
Why do gardeners always drain the water from the pipes in their garden plots before the onset of winter? (When water freezes, it expands and therefore, to prevent the pipes from bursting, gardeners drain the water)
Water gets into the smallest cracks in the rocks, causing the rocks to collapse. What property of water is this related to? (The destruction of rocks is due to the expansion of water when it freezes)
It is known that when heated for a long time, water boils. The boiling point is one hundred degrees. Boiling water is used in everyday life and in production. Where in nature can you find hot water? (In geysers).

When heated and boiled, steam rises above the water - evaporation occurs. Let's write down the definition (working with notebooks) in our notebooks.

Evaporation is the transformation of liquid water into gaseous water.

Evaporation occurs at any temperature, but at higher temperatures evaporation occurs more quickly. For example: puddles dry up after rain both in hot summer and cold autumn, but in summer they dry out faster than in autumn.

EXPERIENCE 3:

(The experience is demonstrated by a group of students as completed homework)

Equipment: measuring cup, 3 cups, 4 identical glasses.

Substance:

water..

Student: We took a measuring cup and measured 100 ml of water into each cup. Cups of water were placed one on the windowsill, another on the table, the third near the radiator. The next day the results were compared. We took identical glasses, poured 100 ml of water into the first one (control), and poured water from the cups into the other three. We compare the results obtained: the water from the cup standing on the windowsill evaporated by one third, in the cup that stood on the table - by half, and the cup standing by the radiator was completely dry - the water evaporated completely. Let us conclude: the higher the ambient temperature, the faster evaporation occurs.

Teacher: We will get acquainted with the significance of evaporation in the life of humans and animals on the pages of the textbook (working with the textbook).

Answer me the questions for consolidation.

What is water evaporation? (Conversion of liquid water into gaseous water)
How do temperature and wind affect water evaporation? (The higher the temperature and the stronger the wind, the faster evaporation occurs)
When will laundry dry faster: in windy or calm weather? (On a windy day)

Let's look at another experiment.

EXPERIENCE 4:

Equipment:

alcohol lamp,
tripods,
flask with gas outlet tube,
metal plate.

Substance:

water.

We heat the flask with water on an alcohol lamp so that the water boils, and bring a cold plate to the gas outlet tube. The steam settles on the plate in the form of droplets.

Conclusion: gaseous water is converted into liquid.

This process is called condensation.

(Write in notebooks)

Condensation is the conversion of water vapor into water.

Where do we meet this phenomenon? We find out from the story.

Student: We encounter condensation of water vapor in everyday life. On a summer evening or early morning, when the air is colder, dew falls. This is water vapor in the air that, when cooled, settles on grass, leaves and other objects in the form of small droplets of water. Clouds also form as a result of condensation of water vapor. Rising above the ground and bodies of water into the upper, colder layers of air, this vapor forms clouds consisting of small droplets of water. If the air temperature is low enough, the water droplets freeze. Snow and sometimes hail fall from such clouds.

Teacher: Thank you for message.

Now let's do some laboratory work. On the tables you have everything you need for work: chemical utensils and substances: water, chalk, salt.

Take salt and dissolve in water. What are you observing? (The salt has dissolved). We received a salt solution.

This can be written schematically like this:

solvent + solute = solution

water + salt = salt solution

Now let’s take chalk, dissolve it in water and compare it with a salt solution. What are we observing? (The chalk solution is cloudy). Let's filter the resulting solution. What are we seeing? (The filtrate is clear, but there is sediment left on the filter). The original liquid is called a suspension.

Conclusion:

if particles of a substance are not visible in water and pass through the filter together with water, then such a substance is called soluble, and the state is called a solution.
if a substance floats in water and lingers on the filter, then this substance is not soluble, but is suspended.

Water is such a unique solvent that it has the most respectful respect.

Today we got acquainted with the properties of water. Now you know that water expands when heated, contracts when cooled, and expands when frozen. You also know what evaporation and condensation are and what their significance is, what solution and suspension are. Now let’s check how you have learned the new material.

Independent work using cards

(Add the necessary words instead of dots)

Water when heated………………………………………………………..
Cooling water…………………………………………………………
Water when frozen……………………………………………………….
Water boils at a temperature of …………………………………………………
The transformation of liquid water into gaseous water is …………………………..
The transformation of steam into water is ……………………………………………….
What is a solution?
………………………………………………………………

How to distinguish a solution from a suspension?

………………………………………………………………..

We hand over the work. This concludes our lesson. Thanks to all. Goodbye. To the question Why does water expand in volume when cooled, when other substances contract when cooled? given by the author Pavel Anufriev
The increase in volume is explained by the fact that each molecule in the ice structure is connected by hydrogen bonds to four other molecules. As a result, in the ice phase, an openwork structure is formed with “cavities” between fixed water molecules, which causes a significant expansion of the entire frozen mass. The crystal structure of ice resembles the structure of diamond: each H2O molecule is surrounded by the four molecules closest to it, participating in the formation of a hydrogen bond and located at equal distances from it, equal to 2.76 angstroms and located at the vertices of a regular tetrahedron at angles equal to 109°28" ( see figure). Due to the low coordination number, the structure of the ice is reticular, which affects its low density. The openwork structure of the ice leads to the fact that its density, equal to 916.7 kg/m³ at 0 °C, is lower than the density of water ( 999.8 kg/m³) at the same temperature.
Therefore, water, turning into ice, increases its volume by about 9%:

During the melting process, at 0 °C, approximately 10-15% of the water loses its bonds with compounds, as a result, the mobility of some molecules increases, and they plunge into those cavities with which the openwork structure of the ice is rich. This explains the compression of ice during melting and the higher density of the resulting water, which increases by about 10%. We can assume that this value in a certain way characterizes the number of water molecules trapped in the cavities. The density of the resulting water reaches a maximum at a temperature of 4 °C, and with a further increase in temperature, the natural expansion of water associated with increased molecular movement exceeds the effect of the “ice-water” structural rearrangement, and the density of water begins to gradually decrease.

Answer from 2 answers[guru]

Hello! Here is a selection of topics with answers to your question: Why does water expand in volume when cooled, when other substances contract when cooled?

Answer from Placer[newbie]
Water does not expand when cooled. Only after the water hardens and becomes ice, only then will its volume increase due to the increase in the distance between the water molecules.

Answer from Mike Tiaroff[guru]
water also contracts... the question is posed incorrectly. . water contracts to -4 degrees, and then expands... This is called a phase transition, and during such transitions substances behave in completely unimaginable ways... when heated to 100 degrees, expansion occurs, but the temperature does not rise above, but a transition to steam occurs - also a phase transition... the bonds between molecules acquire different properties - crystallization begins in water...