Matter in Our Surroundings
As we look around us, we see many different things. These things have different shapes, sizes, and textures. Everything in the universe is made of material that scientists call matter. The air we breathe, the food we eat, stones, clouds, stars, plants, animals, a drop of water, or a grain of sand – all are examples of matter. Matter occupies space and has mass. In other words, matter has both mass and volume.
Early Indian philosophers classified matter into five basic elements called the "Panch Tatva": air, earth, fire, sky, and water. They believed that everything, living or nonliving, was made of these five elements. Ancient Greek philosophers had a similar classification.
Modern scientists classify matter based on its physical properties and chemical nature. In this chapter, we will focus on the physical properties of matter.
For a long time, there were two different ideas about the nature of matter. One idea was that matter is continuous, like a block of wood. The other idea was that matter is made up of tiny particles, like grains of sand. Let's do an activity to find out if matter is continuous or made of particles.
To determine if matter is continuous or particulate.
The salt or sugar seems to disappear into the water, but the water level doesn't change much.
The salt or sugar is made up of particles that spread throughout the water, filling the spaces between the water particles. This supports the idea that matter is made up of particles.
When we dissolve salt in water, the particles of salt get into the spaces between the particles of water.
Matter is made of particles, but how small are these particles? Let’s investigate.
To estimate how small the particles of matter are.
Even after several dilutions, the water is still colored, although the color becomes lighter with each dilution.
A few crystals of potassium permanganate can color a large volume of water. This means that there must be millions of tiny particles in just one crystal of potassium permanganate, which keep dividing into smaller and smaller particles. The particles of matter are incredibly small, beyond our imagination!
The same activity can be done using 2 mL of Dettol instead of potassium permanganate. The smell can be detected even on repeated dilution.
In Activities 1.1 and 1.2, we saw that particles of sugar, salt, Dettol, or potassium permanganate got evenly distributed in water. Similarly, when we make tea, coffee, or lemonade (nimbu paani), particles of one type of matter get into the spaces between particles of the other. This shows that there is enough space between particles of matter.
To demonstrate that particles of matter are continuously moving.
You need to be very close to the unlit incense stick to smell it. However, you can smell the lit incense stick from a distance.
The particles from the lit incense stick move faster due to the heat, allowing the smell to reach you from a distance. This shows that particles of matter are continuously moving.
To demonstrate diffusion in liquids.
The ink spreads quickly throughout the water. The honey spreads much more slowly.
The particles of ink and honey move and mix with the water particles. This movement is called diffusion. Ink diffuses faster than honey because it is less viscous.
To investigate the effect of temperature on diffusion.
The color spreads faster in the hot water than in the cold water.
The rate of mixing (diffusion) increases with temperature. This is because the particles move faster at higher temperatures.
From the above three activities (1.3, 1.4, and 1.5), we can conclude the following:
Particles of matter are continuously moving, meaning they have kinetic energy. As temperature increases, particles move faster, so kinetic energy also increases.
The intermixing of particles of two different types of matter on their own is called diffusion. Heating makes diffusion faster because particles move faster and have more kinetic energy at higher temperatures.
To demonstrate the force of attraction between particles of matter.
The group touching only fingertips is the easiest to break, while the group with locked arms is the hardest.
The force of attraction between particles varies. The group that was harder to break had particles (students) holding each other with greater force.
To compare the force of attraction between particles in different materials.
The iron nail is the most difficult to break, while the chalk is the easiest.
The particles in the iron nail are held together with greater force than the particles in chalk or a rubber band.
To demonstrate the force of attraction between water molecules.
You cannot easily cut the surface of the water.
The water molecules are held together by a force of attraction, which prevents you from easily cutting the surface.
The above three activities (1.6, 1.7, and 1.8) suggest that particles of matter have a force acting between them, keeping them together. The strength of this force varies from one kind of matter to another.
Which of the following are matter? Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume.
Answer: Chair, air, almonds, lemon water.
Give reasons for the following observation: The smell of hot sizzling food reaches you several meters away, but to get the smell from cold food you have to go close.
Answer: The particles of hot food have more kinetic energy and diffuse faster, so the smell travels further.
A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Answer: This shows that the particles of matter have space between them and that the force of attraction between them is not strong enough to prevent the diver from separating them.
What are the characteristics of the particles of matter?
Answer: Particles of matter:
Matter around us exists in three different states: solid, liquid, and gas. These states arise because of differences in the characteristics of the particles of matter.
To identify the characteristics of solids.
The items have definite shapes, distinct boundaries, and fixed volumes. They are difficult to compress.
Solids have a definite shape, distinct boundaries, and fixed volumes, meaning they have negligible compressibility. Solids tend to maintain their shape when subjected to an outside force and are rigid.
Solids have a definite shape, distinct boundaries, and fixed volumes, meaning they have negligible compressibility. Solids tend to maintain their shape when subjected to an outside force. Solids may break under force, but it is difficult to change their shape, so they are rigid.
Consider the following:
(a) What about a rubber band? Can it change its shape on stretching? Is it a solid?
(b) What about sugar and salt? When kept in different jars, these take the shape of the jar. Are they solid?
(c) What about a sponge? It is a solid, yet we can compress it. Why?
All the above are solids because:
To identify the characteristics of liquids.
Liquids have no fixed shape but have a fixed volume. They take the shape of the container they are kept in. Liquids flow easily.
Liquids have no fixed shape but have a fixed volume. They take up the shape of the container in which they are kept. Liquids flow and change shape, so they are not rigid but can be called fluid.
Refer to activities 1.4 and 1.5 where we saw that solids and liquids can diffuse into liquids. Gases from the atmosphere diffuse and dissolve in water. These gases, especially oxygen and carbon dioxide, are essential for the survival of aquatic animals and plants.
All living creatures need to breathe for survival. Aquatic animals can breathe underwater due to the presence of dissolved oxygen in water. Thus, we may conclude that solids, liquids, and gases can diffuse into liquids. The rate of diffusion of liquids is higher than that of solids because, in the liquid state, particles move freely and have greater space between each other compared to particles in the solid state.
Have you ever watched a balloon seller filling balloons from a single cylinder of gas? They can fill many balloons from just one cylinder. This is because gases can be compressed into a small space.
To demonstrate the compressibility of gases.
The piston is easily pushed in when the syringe is filled with air (gas). It is more difficult to push in when filled with water (liquid), and very difficult when filled with chalk (solid).
Gases are highly compressible compared to solids and liquids.
We have observed that gases are highly compressible compared to solids and liquids. Liquefied petroleum gas (LPG) cylinders for cooking and oxygen cylinders in hospitals contain compressed gas. Compressed natural gas (CNG) is used as fuel in vehicles. Due to its high compressibility, large volumes of gas can be compressed into a small cylinder and transported easily.
We can smell food cooking in the kitchen without even going there. The particles of the aroma of food mix with the particles of air and spread. The smell of hot cooked food reaches us in seconds, which is much faster than the rate of diffusion of solids and liquids. Due to the high speed of particles and large space between them, gases show the property of diffusing very fast into other gases.
In the gaseous state, the particles move randomly at high speed. Due to this random movement, the particles hit each other and also the walls of the container. The pressure exerted by the gas is due to the force exerted by gas particles per unit area on the walls of the container.
The mass per unit volume of a substance is called density (density = mass/volume). Arrange the following in order of increasing density: air, exhaust from chimneys, honey, water, chalk, cotton, and iron.
Answer: Air < Exhaust from chimneys < Cotton < Water < Honey < Chalk < Iron
(a) Tabulate the differences in the characteristics of states of matter. (b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy, and density.
Answer:
(a)
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Definite | No fixed shape | No fixed shape |
| Volume | Definite | Definite | No fixed volume |
| Compressibility | Negligible | Low | High |
| Rigidity | Rigid | Not rigid (fluid) | Not rigid (fluid) |
| Kinetic Energy | Low | Intermediate | High |
| Density | High | Intermediate | Low |
(b)
Give reasons:
(a) A gas fills completely the vessel in which it is kept.
(b) A gas exerts pressure on the walls of the container.
(c) A wooden table should be called a solid.
(d) We can easily move our hand in air but to do the same through a solid block of wood, we need a karate expert.
Answer:
(a) The particles in a gas move randomly and have negligible forces of attraction, allowing them to fill the entire vessel.
(b) Gas particles are in constant, random motion, colliding with the walls of the container. These collisions exert a force per unit area, which is pressure.
(c) A wooden table has a definite shape and volume, is rigid, and is difficult to compress, which are all characteristics of a solid.
(d) Air particles have large spaces between them and weak forces of attraction, allowing us to move our hand easily. Wood particles are closely packed with strong forces of attraction, making it difficult to move our hand through it.
Liquids generally have lower density compared to solids. But you must have observed that ice floats on water. Find out why.
Answer: Ice has a lower density than water because, in its solid structure, the water molecules form a cage-like structure with more space between them than in liquid water. This makes ice less dense, allowing it to float.
We know that water can exist in three states of matter:
What happens inside the matter during this change of state? What happens to the particles of matter during the change of states? How does this change of state take place?
To investigate the effect of temperature on the state of matter.
As the ice is heated, its temperature rises until it reaches . At this point, the ice starts melting, and the temperature remains constant until all the ice has melted. Once all the ice has melted, the temperature of the water rises until it reaches . At this point, the water starts boiling, and the temperature remains constant until all the water has vaporized.
Increasing the temperature of a solid increases the kinetic energy of its particles, causing them to vibrate faster. Eventually, the particles overcome the forces of attraction holding them in place, and the solid melts into a liquid. Further heating increases the kinetic energy of the liquid particles until they overcome the forces of attraction and the liquid boils into a gas.
On increasing the temperature of solids, the kinetic energy of the particles increases. Due to the increase in kinetic energy, the particles start vibrating with greater speed. The energy supplied by heat overcomes the forces of attraction between the particles. The particles leave their fixed positions and start moving more freely. A stage is reached when the solid melts and is converted to a liquid. The minimum temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.
The melting point of a solid indicates the strength of the force of attraction between its particles.
The melting point of ice is . The process of melting, which is the change of solid state into liquid state, is also known as fusion.
When a solid melts, its temperature remains the same, so where does the heat energy go?
During melting, the temperature of the system does not change after the melting point is reached until all the ice melts. This happens even though we continue to heat the beaker, meaning we continue to supply heat. This heat is used to change the state by overcoming the forces of attraction between the particles. As this heat energy is absorbed by ice without showing any rise in temperature, it is considered that it gets hidden into the contents of the beaker and is known as the latent heat. The word latent means hidden. The amount of heat energy required to change 1 kg of a solid into a liquid at atmospheric pressure at its melting point is known as the latent heat of fusion. So, particles in water at () have more energy than particles in ice at the same temperature.
When we supply heat energy to water, particles start moving even faster. At a certain temperature, a point is reached when the particles have enough energy to break free from the forces of attraction of each other. At this temperature, the liquid starts changing into gas. The temperature at which a liquid starts boiling at atmospheric pressure is known as its boiling point. Boiling is a bulk phenomenon. Particles from the bulk of the liquid gain enough energy to change into the vapor state.
For water, this temperature is ().
Latent heat of vaporization is the heat energy required to change 1 kg of a liquid into gas at atmospheric pressure at its boiling point. Particles in steam, meaning water vapor at (), have more energy than water at the same temperature. This is because particles in steam have absorbed extra energy in the form of latent heat of vaporization.
So, we infer that the state of matter can be changed into another state by changing the temperature.
Substances around us change state from solid to liquid and from liquid to gas on the application of heat. However, some substances change directly from solid state to gaseous state and vice versa without changing into the liquid state.
To demonstrate sublimation.
The solid camphor gradually disappears from the china dish without melting, and a solid deposit forms on the inner walls of the funnel.
The camphor changes directly from a solid to a gas without becoming a liquid. This process is called sublimation.
A change of state directly from solid to gas without changing into the liquid state is called sublimation, and the direct change of gas to solid without changing into the liquid is called deposition.
The difference in various states of matter is due to the difference in the distances between the constituent particles. What will happen when we start putting pressure and compress a gas enclosed in a cylinder? Will the particles come closer? Can increasing or decreasing the pressure change the state of matter?
Applying pressure and reducing temperature can liquefy gases.
Have you heard of solid carbon dioxide ()? It is stored under high pressure. Solid gets converted directly into the gaseous state when the pressure decreases to 1 atmosphere without coming into the liquid state. This is the reason that solid carbon dioxide is also known as dry ice.
Thus, we can say that pressure and temperature determine the state of a substance, whether it will be solid, liquid, or gas.
Convert the following temperature to the Celsius scale: a. 300 K b. 573 K
Answer:
a.
b.
What is the physical state of water at: a. b. ?
Answer:
a. Gas (steam)
b. Gas (steam) and Liquid (boiling)
For any substance, why does the temperature remain constant during the change of state?
Answer: The temperature remains constant because the heat energy supplied is used to overcome the forces of attraction between the particles, allowing them to change state, rather than increasing their kinetic energy.
Suggest a method to liquefy atmospheric gases.
Answer: Atmospheric gases can be liquefied by applying pressure and reducing temperature.
Do we always need to heat or change pressure for changing the state of matter? Can you think of some examples from everyday life where a liquid changes to a vapor without reaching the boiling point? Water, when left uncovered, slowly changes into vapor. Wet clothes dry up. What happens to the water in these examples?
Particles of matter are always moving and are never at rest. At a given temperature in any gas, liquid, or solid, there are particles with different amounts of kinetic energy. In liquids, a small fraction of particles at the surface with higher kinetic energy can break away from the forces of attraction of other particles and become vapor. This change of a liquid into vapors at any temperature below its boiling point is called evaporation.
Let's understand this with an activity.
To investigate the factors affecting evaporation.
The water in the open china dish evaporates faster than the water in the test tube. The water evaporates faster under a fan than inside a cupboard. The water evaporates more slowly on a rainy day.
The rate of evaporation increases with an increase in surface area, an increase in temperature, a decrease in humidity, and an increase in wind speed.
The rate of evaporation increases with:
In an open vessel, the liquid keeps evaporating. The particles of liquid absorb energy from the surrounding to regain the energy lost during evaporation. This absorption of energy from the surroundings makes the surroundings cold.
When you pour some acetone (nail polish remover) on your palm, the particles gain energy from your palm or surroundings and evaporate, causing the palm to feel cool.
After a hot sunny day, people sprinkle water on the roof or open ground because the large latent heat of vaporization of water helps to cool the hot surface.
We can feel the effect of cooling due to evaporation in daily life. For example, we should wear cotton clothes in summer.
During summer, we perspire more because our body has a mechanism that keeps us cool. During evaporation, the particles at the surface of the liquid gain energy from the surroundings or body surface and change into vapor. The heat energy equal to the latent heat of vaporization is absorbed from the body, leaving the body cool. Cotton is a good absorber of water, helping absorb sweat and expose it to the atmosphere for easy evaporation.
We see water droplets on the outer surface of a glass containing ice-cold water because the water vapor present in the air, on coming in contact with the cold glass of water, loses energy and gets converted to the liquid state, which we see as water droplets.
Why does a desert cooler cool better on a hot dry day?
Answer: On a hot dry day, the humidity is low, which increases the rate of evaporation. The evaporation of water from the desert cooler absorbs heat from the surroundings, resulting in a cooling effect.
How does the water kept in an earthen pot (matka) become cool during summer?
Answer: Earthen pots have tiny pores through which water seeps out to the surface. This water evaporates, absorbing heat from the pot and the remaining water, resulting in a cooling effect.
Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Answer: Acetone, petrol, and perfume are volatile liquids that evaporate quickly. As they evaporate, they absorb heat from our palm, causing a cooling sensation.
Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
Answer: A saucer has a larger surface area than a cup. This increases the rate of evaporation, which cools the tea or milk faster, allowing us to sip it more quickly.
What type of clothes should we wear in summer?
Answer: We should wear cotton clothes in summer because cotton is a good absorber of water. It helps absorb sweat and exposes it to the atmosphere for easy evaporation, which cools our body.
Great job reading through all sections. Ready to test your knowledge and reinforce your learning?