Comprehensive Notes on Matter in Our Surroundings

Matter in Our Surroundings

Introduction

• Everything in the universe is made up of "matter," which has different shapes, sizes, and textures.
• Matter occupies space and has mass, meaning it has both mass and volume.
• Early Indian philosophers classified matter into five basic elements called "Panch Tatva": air, earth, fire, sky, and water.
• Ancient Greek philosophers had a similar classification of matter.
• Modern scientists classify matter based on physical properties and chemical nature.

1.1 Physical Nature of Matter

1.1.1 Matter is Made Up of Particles

• Two schools of thought existed regarding the nature of matter:
  • One believed matter to be continuous (like a block of wood).
  • The other believed matter was made up of particles (like sand).
• Activity 1.1 demonstrates that matter is made up of particles.
  • When salt or sugar is dissolved in water, it spreads throughout the water.
  • This indicates that the salt or sugar is made up of particles that occupy the spaces between water particles. Refer to Fig 1.1.

1.1.2 How Small Are These Particles of Matter?

• Activity 1.2 demonstrates the small size of matter particles.
  • Dissolving 2-3 crystals of potassium permanganate in 100 mL of water, and then diluting this solution repeatedly (5-8 times), still results in colored water.
  • This implies that one crystal of potassium permanganate contains millions of tiny particles that keep dividing into smaller particles.
  • The same activity can be done using 2 mL of Dettol instead of potassium permanganate; the smell can be detected even on repeated dilution.
  • The particles of matter are very small – they are small beyond our imagination.
  • Refer to Fig 1.2 Estimating how small are the particles of matter. With every dilution, though the colour becomes light, it is still visible. This experiment shows that just a few crystals of potassium permanganate can colour a large volume of water (about 1000 L).

1.2 Characteristics of Particles of Matter

1.2.1 Particles of Matter Have Space Between Them

• Activities 1.1 and 1.2 show that particles of sugar, salt, Dettol, or potassium permanganate get evenly distributed in water.
• When making tea, coffee, or lemonade, 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.

1.2.2 Particles of Matter Are Continuously Moving

• Activity 1.3: Demonstrates the movement of particles.
  • An unlit incense stick's smell can only be detected up close.
  • A lit incense stick's smell can be detected from a distance.
• Activity 1.4: Demonstrates the movement of particles.
  • Ink spreads evenly throughout water over time, while honey takes longer.
• Activity 1.5: Demonstrates the movement of particles and the effect of temperature.
  • A crystal of copper sulfate or potassium permanganate dissolves faster in hot water than in cold water.
• From the above three activities (1.3, 1.4 and 1.5), we can conclude the following:
  • Particles of matter are continuously moving, possessing kinetic energy.
  • As temperature rises, particles move faster, increasing their kinetic energy.
  • Particles of matter intermix on their own by getting into the spaces between them; this is called diffusion.
  • Diffusion becomes faster on heating.

1.2.3 Particles of Matter Attract Each Other

• Activity 1.6: Demonstrates the force of attraction between particles.
  • Four groups form human chains by holding each other in different ways.
  • The group holding each other tightly is the hardest to break.
  • Refer to Fig 1.3.
• Activity 1.7: Demonstrates the force of attraction between particles.
  • Trying to break an iron nail, a piece of chalk, and a rubber band shows that the iron nail requires more force.
• Activity 1.8: Demonstrates the force of attraction between particles.
  • Trying to cut the surface of water with fingers is not easy because the water surface remains together.
• The above three activities (1.6, 1.7 and 1.8) suggest that particles of matter have force acting between them.
• This force keeps the particles together; the strength of this force varies from one kind of matter to another.

1.3 States of Matter

• Matter exists in three different states: solid, liquid, and gas.
• These states arise due to the variation in the characteristics of the particles of matter.

1.3.1 The Solid State

• Activity 1.9: Demonstrates the properties of solids.
  • Collecting a pen, a book, a needle, and a piece of wooden stick shows that they have definite shapes, distinct boundaries, and fixed volumes.
  • They are difficult to compress.
• Solids have a tendency to maintain their shape when subjected to outside force; they may break under force but it is difficult to change their shape, so they are rigid.
• Consider the following:
  • A rubber band changes shape under force and regains the same shape when the force is removed. If excessive force is applied, it breaks. It is a solid.
  • The shape of each individual sugar or salt crystal remains fixed, whether we take it in our hand, put it in a plate or in a jar. They are solid.
  • A sponge has minute holes, in which air is trapped, when we press it, the air is expelled out and we are able to compress it. It is a solid.
• Examples of solids: pen, book, needle, wooden stick

1.3.2 The Liquid State

• Activity 1.10: Demonstrates the properties of liquids.
  • Collecting water, cooking oil, milk, juice, a cold drink shows that they take the shape of the container in which they are kept.
  • Liquids have no fixed shape but have a fixed volume.
• Liquids flow and change shape, so they are not rigid but can be called fluid.
• Solids and liquids can diffuse into liquids, as seen in activities 1.4 and 1.5.
• Gases from the atmosphere diffuse and dissolve in water, which is essential for aquatic animals and plants.
• The rate of diffusion of liquids is higher than that of solids because particles in the liquid state move more freely and have greater space between them as compared to particles in the solid state.

1.3.3 The Gaseous State

• Activity 1.11: Demonstrates the properties of gases.
  • Taking three 100 mL syringes, filling one with water, one with chalk pieces, and leaving one empty, and then trying to compress the contents shows that gases are highly compressible.
  • Refer to Fig 1.4.
• Gases are highly compressible as compared to solids and liquids.
• Liquefied petroleum gas (LPG) and compressed natural gas (CNG) are examples of compressed gases.
• Due to high compressibility, large volumes of a gas can be compressed into a small cylinder and transported easily.
• The smell of hot cooked food reaches us quickly because the particles of the aroma of food mix with the particles of air and spread rapidly.
• Due to 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 about 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 because of this force exerted by gas particles per unit area on the walls of the container.
• Fig.1.5: a, b and c show the magnified schematic pictures of the three states of matter. The motion of the particles can be seen and compared in the three states of matter.

1.4 Can Matter Change its State?

• Water can exist in three states of matter: solid (ice), liquid (water), and gas (water vapor).

1.4.1 Effect of Change of Temperature

• Activity 1.12: Demonstrates the effect of temperature on the state of matter.

  • Heating ice in a beaker causes it to melt into water, and further heating causes the water to vaporize.
  • Refer to Fig 1.6: (a) Conversion of ice to water, (b) conversion of water to water vapour

• Increasing the temperature of solids increases the kinetic energy of the particles, causing them to vibrate with greater speed.

• The energy supplied by heat overcomes the forces of attraction between the particles, and they 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 $273.15 K$

• The process of melting (change of solid state into liquid state) is also known as fusion.

• When a solid melts, its temperature remains the same because the heat energy is used up in changing the state by overcoming the forces of attraction between the particles.

• 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 amount of heat energy required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point is known as the latent heat of fusion.

• Particles in water at $0^\circ C$ ($273 K$) have more energy as compared to particles in ice at the same temperature.

• When heat energy is supplied to water, particles start moving even faster.

• At a certain temperature, the liquid starts changing into gas.

• The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point.

• Boiling is a bulk phenomenon where particles from the bulk of the liquid gain enough energy to change into the vapor state.

• For water, this temperature is $373 K$ ($100^\circ C = 273 + 100 = 373 K$).

• Particles in steam (water vapor at $373 K$ ($100^\circ C$)) have more energy than water at the same temperature because they have absorbed extra energy in the form of latent heat of vaporization.

• Kelvin is the SI unit of temperature. $0^\circ C = 273.15 K$. For convenience, we take $0^\circ C = 273 K$ after rounding off the decimal.

• To change a temperature on the Kelvin scale to the Celsius scale, subtract 273 from the given temperature, and to convert a temperature on the Celsius scale to the Kelvin scale, add 273 to the given temperature.

• The state of matter can be changed into another state by changing the temperature.

• Substances change state from solid to liquid and from liquid to gas on application of heat.

• Some substances change directly from solid state to gaseous state and vice versa without changing into the liquid state.

• Activity 1.13: Demonstrates sublimation.

  • Heating camphor in a china dish covered with an inverted funnel causes it to change directly from solid to gas.
  • Refer to Fig 1.7: Sublimation of camphor

• A change of state directly from solid to gas without changing into liquid state is called sublimation and the direct change of gas to solid without changing into liquid is called deposition.

1.4.2 Effect of Change of Pressure

• The difference in various states of matter is due to the difference in the distances between the constituent particles.
• Applying pressure and reducing temperature can liquefy gases.
• Applying pressure, particles of matter can be brought close together.
• Increasing or decreasing the pressure can change the state of matter.
• Solid carbon dioxide (CO2) gets converted directly into gaseous state on decrease of pressure to 1 atmosphere without coming into liquid state. This is the reason that solid carbon dioxide is also known as dry ice.
• Pressure and temperature determine the state of a substance, whether it will be solid, liquid, or gas.
• Refer to Fig 1.8: By applying pressure, particles of matter can be brought close together
• Refer to Fig 1.9: Interconversion of the three states of matter

1.5 Evaporation

• Change of state from liquid to vapor can take place without the liquid reaching the boiling point.
• Water, when left uncovered, slowly changes into vapor. Wet clothes dry up.
• 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 the case of liquids, a small fraction of particles at the surface, having higher kinetic energy, is able to break away from the forces of attraction of other particles and gets converted into vapor.
• This phenomenon of change of liquid into vapors at any temperature below its boiling point is called evaporation.

1.5.1 Factors Affecting Evaporation

• Activity 1.14: Demonstrates the factors affecting evaporation.
  • Taking water in a test tube, an open china dish near a window, and an open china dish inside a cupboard shows that evaporation is affected by surface area, temperature, and wind velocity.
• The rate of evaporation increases with:
  • An increase of surface area: Evaporation is a surface phenomenon; increasing the surface area increases the rate of evaporation.
  • An increase of temperature: Increasing the temperature gives more particles enough kinetic energy to go into the vapor state.
  • A decrease in humidity: Humidity is the amount of water vapor present in the air; if the air is already high in water vapor, the rate of evaporation decreases.
  • An increase in wind speed: Increasing the wind speed moves the particles of water vapor away, decreasing the amount of water vapor in the surrounding.

1.5.2 How Does Evaporation Cause Cooling?

• In an open vessel, the liquid keeps on evaporating.
• The particles of liquid absorb energy from the surrounding to regain the energy lost during evaporation, making the surroundings cold.
• Pouring acetone (nail polish remover) on your palm causes the particles to gain energy from your palm or surroundings and evaporate, causing a cooling sensation.
• Sprinkling water on the roof or open ground after a hot sunny day cools the surface due to the large latent heat of vaporization of water.
• During summer, we perspire more because of the mechanism of our body which 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, being a good absorber of water helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation.
• Water droplets on the outer surface of a glass containing ice-cold water are formed because the water vapor present in air, on coming in contact with the cold glass of water, loses energy and gets converted to liquid state.

Definitions and Units

• Mass: The SI unit of mass is kilogram (kg).
• Volume: The SI unit of volume is cubic metre ($m^3$). The common unit of measuring volume is litre (L) such that $1L = 1 dm^3$, $1L = 1000 mL$, $1 mL = 1 cm^3$.
• Melting Point: The minimum temperature at which a solid melts to become a liquid at atmospheric pressure.
• Boiling Point: The temperature at which a liquid starts boiling at atmospheric pressure.
• Sublimation: The change of solid state directly to gaseous state without going through liquid state.
• Deposition: The change of gaseous state directly to solid state without going through liquid state.
• Evaporation: The phenomenon of change of liquid into vapors at any temperature below its boiling point.
• Latent Heat of Vaporization: The heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point.
• Latent Heat of Fusion: The amount of heat energy required to change 1 kg of solid into liquid at its melting point.
• Density: mass/volume, Unit: kilogram per cubic metre ($kg/m^3$)
• Pressure: Unit pascal (Pa); 1 atmosphere = $1.01 × 10^5 Pa$