Changing of States of Matter

As we discussed the concept of “States of Matter” in the previous lesson, we shall further discuss the “Changing of States of Matter” in this lesson. But, before we proceed, let us quickly refresh your knowledge of “States of Matter”

1. Matter exists in three primary states: solid, liquid, and _______.

2. In a liquid state, particles are _______ packed but can move past each other, allowing the liquid to flow.

3. In the _______ state of matter, particles are tightly packed and have a fixed shape and volume.
   
   

Answer to Q.No.1 - Gas

Answer to Q No.2 - Loosely

Answer to Q No.3 - Solid

Three States of Matter

As you are aware, the three States of Matter are Solid, Liquid, and Gas. These forms of matter are present everywhere around us. But are you aware that these states of matter can change their form from one to another on heating and cooling? 

 

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What are the changes in the state of matter process?

The changes in the states of matter take place when matter loses or absorbs energy. If the substance absorbs energy, then the atoms and molecules present inside the substance are boosted to move faster. At the same time, the excess kinetic energy pushes the particles to an extent to change their form. This is mostly in the form of heat or thermal energy. Similarly, if the substance loses energy, its temperature changes causing it to change its form. We shall explain below how this happens.

 

What changes happen between liquid and solid?

If a solid cube of ice is placed in a bowl, what happens to it? It melts at room temperature. Similarly, if a bowl of water is placed in a Freezer, what happens to it? It freezes. But ever wondered, how this happens? Let us explore further:

Melting

Melting is a process in which a solid substance gets converted into liquid. This takes place due to heat energy. As stated above, if ice cubes are placed in a warm room, the ice absorbs the warmth from the atmosphere, and the absorbed energy breaks up the force of attraction held between the molecules. This causes melting and the ice changes into liquid. Similarly, when a bar of butter or chocolate is heated, it melts and converts into melted butter and melted chocolate. With the same principle, snow melts under the heat of the Sun and gets converted to water.

 

Test your Understanding

1. What happens when a solid substance melts?

a) It changes from a solid to a gaseous state

b) It changes from a solid to a liquid state

c) It changes from liquid to solid state

 

2. What causes Melting?

a) Heat

b) Cold

c) Frost

Freezing

Freezing is a process that changes a liquid substance into a solid substance. It happens in the absence of heat and when the temperature falls below the freezing point. The particles lose their energy and move more slowly when heat is removed from a liquid. This makes the particles come closer to each other and form a solid structure. The freezing point of a substance is the temperature at which the liquid turns into a solid. For example, water freezes at 0°C. Freezing is a reversible process; which means, a substance that freezes can change again to become a liquid.

 

Test your Understanding

 

1. What happens when a liquid substance freezes?

a) It changes from a liquid to a gaseous state

b) It changes from a solid to a liquid state

c) It changes from liquid to solid state

 

2. What causes Freezing?

a) When the temperature falls below the freezing point

b) When the temperature reaches the boiling point

c) When the temperature remains constant

 

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What changes happen between liquids and gases?

A rise in temperature changes a substance from a liquid state to a gaseous state. When you heat a pot of water in a gas stove, the heat energy passes from the flame to the pot and from the pot to the water inside. When the water absorbs the heat, it changes from liquid to gas. Similarly, when the water vapor is cooled, it changes again from a gaseous state to a liquid. These concepts are explained below: 

Evaporation

Evaporation is a process in which a liquid changes into a gas or vapor without reaching its boiling point. The main cause of evaporation is heat. It is a natural process when the liquid molecules present at the surface obtain enough energy to escape from the liquid. The higher the temperature, the faster the evaporation rate. 

 

Test your Understanding

 

1. What happens when a liquid evaporates?

a) It changes from a liquid to a gaseous state

b) It changes from a solid to a liquid state

c) It changes from liquid to solid state

 

2. What causes Evaporation?

a) When the temperature falls

b) When the temperature rises

c) When the temperature remains constant

Condensation

Condensation is the process in which the water vapor changes from a gaseous state to a liquid state. In short, it is the conversion of water vapor into liquid water. Warm air contains moisture in it. When it comes in contact with a cold surface, it cools down and accumulates in the form of liquid droplets on the cool surface. It is the reverse form of Evaporation. So, water droplets on the outside surface of a glass filled with a cold drink, dew drops collected in the grass on a winter morning, a foggy atmosphere in frosty weather, and clouds in the sky are all examples of Condensation.

 

Test your Understanding

1. What happens when a liquid condenses?

a) It changes from a liquid state to a gaseous state

b) It changes from a gaseous state to a liquid state

c) It changes from a liquid state to a solid state

 

2. What causes Condensation?

a) When cold air hits a warm surface

b) When warm, moist air hits a cold surface

c) When cold air is let loose in the atmosphere

 

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What changes happen between Solids and gases?

Sometimes, a substance changes from a solid state directly into a gaseous state without changing into a liquid state. Here, the solid takes in so much energy that it can break free from the forces holding its molecules together. So what is this process called? The same is explained below:

Sublimation

Sublimation is a change of state directly from the solid to the gas state without passing through the liquid state. Sublimation is due to the absorption of heat, providing enough energy to overcome some of the attractive forces of the molecules, and they escape to the vapor phase. Examples of sublimation include dry ice turning into carbon dioxide at room temperature and pressure. Naphthalene sublimes easily under standard pressure and temperature. Dry Ice, Naphthalene balls, iodine, and camphor are some examples of Sublimation

Test your Understanding

1. What happens when a solid substance sublimates?

a) It changes from a liquid state to a gaseous state

b) It changes from a gaseous state to a liquid state

c) It changes from a solid state directly to a gaseous state

 

2. Which of the following states is skipped and does not occur during sublimation?

a) Solid

b) Liquid

c) Gas

Deposition

Deposition is the opposite of Sublimation. Hence, sometimes it is also called Desublimation. In this process, the gas directly transforms into a solid without touching the liquid state. Deposition is also employed in the formation of frost. You can also observe deposition if you watch a freezer in a moist climate, or on cold metal, and windows during winter. Another example would be the frosting on a leaf. Deposition will only occur if the thermal energy is removed from the gas. When the air gets cool enough, water vapor in the surrounding air near the leaf loses sufficient thermal energy to condense into a solid.

Test your Understanding

1. Deposition is the opposite of which phase change?

a) Evaporation

b) Condensation

c) Sublimation

 

2. What is deposition in terms of phase transition?

a) The process of a gas turning into a liquid.

b) The process of a gas turning directly into a solid.

c) The process of a solid turning directly into a gas.

 

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Quiz Questions

1) What is melting?

A. The process of a solid turning into a gas

B. The process of a liquid turning into a gas

C. The process of a solid turning into a liquid

D. The process of a liquid turning into a solid

 

2) What is freezing?

 

A. The process of a solid turning into a liquid

B. The process of a liquid turning into a gas

C. The process of a liquid turning into a solid

D. The process of gas turning into a liquid

3) What is evaporation?

A. The process of a liquid turning into a solid

B. The process of a liquid turning into a gas

C. The process of a solid turning into a gas

D. The process of gas turning into a liquid

4) What is condensation?

A. The process of gas turning into a liquid

B. The process of a liquid turning into a gas

C. The process of a liquid turning into a solid

D. The process of a solid turning into a gas

5) What is sublimation?

A. The process of gas turning into a liquid

B. The process of a solid turning directly into a gas

C. The process of a liquid turning into a gas

D. The process of a solid turning into a liquid