UNIT NO.5
Matter as Particles
(Solved Exercise)
5.1 Encircle the correct option.
5.2 Give short answers.
1. How can we change the physical state of matter?
When some objects are heated movement of their particles become rapid. Ultimately, solids convert into liquids and liquids covert into gases. When some objects are cooled, movements of their particles get slower. Ultimately, gases convert into liquids and liquids convert into solids. It is the movement of the particles that causes change in the physical state of matter.
2. How do liquids differ from gases?
The distance among the gas particles are much greater than in liquids. Liquid does not have a fixed shape, but it has fixed volume. Gases have neither fixed shape nor fixed volume. Liquids cannot be compressed easily and gases can be Compressed easily.
3. How do solids differ from liquids with regard to particles arrangements?
In solids, particles have an orderly arrangement where they are present tightly packed with each other. The forces of attraction between them are the strongest. That is why they have fixed shape and fixed volume. In liquids, the particles are present very close to one another, but, they are not regularly arranged. The attractive forces between them are strong, but, weaker than solids. A liquid does not have a fixed shape, but, it has fixed volume.
4. A liquid on cooling is converted into its solid state. What will happen to a solid when it is cooled?
When a solid is cooled, it will typically undergo a decrease in temperature and maintain its solid state.
5. Write down the names of five liquids and five gases which you know.
Liquids: 1. Water 2. Cooking Oil 3. Milk 4. Petrol 5. Orange juice
Gases: 1. Oxygen 2. Nitrogen 3. Hydrogen 4. Carbon dioxide 5. Helium
5.3 Differentiate the following:
1. Melting and Freezing
Melting:
Melting is the process by which a substance changes from a solid state to a liquid state. Mostly it occurs when solid is heated.
Freezing:
Freezing is the process by which a substance changes from a liquid state to a solid state. Mostly it occurs when liquid is cooled.
2. Boiling and Condensation
Boiling
Boiling is the process by which a substance changes from a liquid state to a gaseous state. Mostly it occurs when liquid is heated.
Condensation
Condensation is the process by which a substance changes from a gaseous state to a liquid state. Mostly it occurs when gas is cooled.
3. Evaporation and Sublimation
Evaporation
When a liquid is kept in an open container, its particles start escaping from its surface into an open atmosphere. This phenomenon is called evaporation ant it takes place any temperature.
Sublimation
by which a Some solids, e.g., iodine, ammonium chloride and naphthalene, etc., when heated, change directly into their gaseous state without undergoing the liquid state. This process is called Sublimation.
4. Diffusion and Compression
Diffusion
The movement of material particles from the area where they are more to the area where they are less is called diffusion of particles.
Compression
Compression is the process of applying force or pressure on something to making it smaller in size or taking up less space.
5.4 Give answer in detail.
1. Explain the use of following process in daily life.
(a) Freezing
Freezing is widely used in daily life for food preservation. Meat, fruit, and vegetables can be preserved longer with freezing. It is utilized in the production of ice which is used as a cooling agent and for making frozen desserts. Vaccines and biological samples are also stored and preserved using freezing process in industries like pharmaceuticals and laboratories.
(b)Boiling
Boiling is commonly used in daily life for cooking food, such as boiling vegetables, pasta, or rice. It is also used to sterilize water, making it safe for drinking and reducing the risk of waterborne diseases. Boiling is utilized in various industrial processes, including the production of steam for generating electricity and manufacturing chemical substances.
(c)Evaporation
Evaporation plays a significant role in daily life for drying wet clothes and laundry. It is used in air conditioning systems, where evaporation of refrigerants helps cool the air and maintain comfortable indoor temperatures. Evaporation is also employed in the process of making various food products like condensed milk and dried fruits.
(e)Condensation
Condensation is commonly used in daily life for collecting and using water through processes like distillation. It is utilized in air conditioning units to remove humidity from the air and cool the environment.
Condensation plays a vital role in the water cycle, where water vapor condenses into clouds and eventually falls as rain or snow.
(f )Melting
The melting process is frequently used in daily life for cooking, such as melting butter or chocolate for recipes.
It is utilized in various applications like candle-making, where solid wax is melted to create the liquid wax needed for pouring into molds. Melting is also essential in metalworking, allowing solid metals to be transformed into a molten state for casting, forging, or welding.
2. Why do solids have fixed volume and fixed shape?
In solids, particles have an orderly arrangement where they are present tightly packed with each other. The forces of attraction between them are the strongest. They cannot move freely, but, vibrate at their fixed positions. That is why they have fixed shape and fixed volume. The spaces among the particles of a solid are negligibly small.
3. Why do solids not flow like liquids and gases?
The forces of attraction between the particles of gases are negligible. So they can move freely in all direction. In liquids, the particles are close together due to strong force of attraction between them but not as tightly packed as in solids. Molecules of water are free to slide and rotate over one another. So liquids can flow. As compare to gases and liquids, in solids, particles have an orderly arrangement where they are present tightly packed with each other. The forces of attraction between them are strongest. So they cannot move freely. That is why solids do not flow like liquids and gases.
4. What is diffusion? explain with examples.
DIFFUSION OF PARTICLES
The movement of material particles from the area where they are more to the area where they are less is called diffusion of particles. Gases diffuse easily because their particles can move freely. Liquids can also diffuse but at slower rate as compared to gases.
Examples of Diffusion
· When we spray a little perfume in one corner of room then after some time we can feel fragrance in the whole room.
· The pleasant smell of being cooked in kitchen reaches the other room of the house.
· When we mix some drop of blue ink in glass of water then after some time all water of glass turn to blue.
It all happen due to diffusion.
5.What is sublimation? Explain with examples.
Mostly, solid objects, when heated melt into their liquid states. If heating is continued, these liquids further change into their gaseous states. Some solids, e.g., iodine, ammonium chloride and naphthalene, etc., when heated, change directly into their gaseous states without undergoing the liquid states. This process is called sublimation.
Conversion of solid carbon dioxide (dry ice) directly into carbon dioxide gas is the best example of sublimation. Dry ice is often used to keep the materials cold and dry.
5.5 Constructed Response Questions
1. The steam and vapours present in air, both are the gaseous state of water.
(a) Why are the vapours in air invisible?
The vapors in the air are invisible because they are made up of tiny particles that are too small to see with our eyes.
(b) Why is the steam in air visible?
Steam in air is visible because it contains tiny water droplets that reflect light.
(c) How are vapours formed?
Vapours are formed when a liquid changes into gas due to heating.
(d) How is steam formed?
steam is specifically formed when water boils and changes into gas.