1. Matter in Our Surroundings Science class 9 in English Medium ncert book solutions Chapter Review

Chapter Review:

• Everything in this universe is made up of material which scientists have named “matter”.
• The air we breathe, the food we eat, stones, clouds, stars, plants and animals, even a small drop of water or a particle of sand– each thing is matter.
• Matters occupy space, that is volume and have mass. 
• Early Indian philosophers classified matter in the form of five basic elements – the “Panch Tatva”– air, earth, fire, sky and water.
• Modern day scientists have evolved two types of classification of matter based on their physical properties and chemical nature.
• Matter is made up of particles.
• Particles of matters have space between them. 
• Particles of matters are continuously moving.
• When the temperature rises, particles move faster. 
• Increasing in temperature the kinetic energy of the particles also increases.
• Particles of matter intermix on their own with each other. They do so by getting into the spaces between the particles.
• Intermixing of particles of two different types of matter on their own is called diffusion.
• Particles of matter attract  each others.
• Particles of matter have force acting between them.
• There are three states of matter, i.e solid, liquid and gas. 
• States of matter arise due to the variation in the characteristics of the particles of matter.
• Solids have a definite shape, distinct boundaries and fixed volumes, that is, have negligible compressibility.
• Solids have a tendency to maintain their shape when subjected to outside force.
• Solids may break under force but it is difficult to change their shape, so they are rigid.
• Liquids have no fixed shape but have a fixed volume.
• Liquids 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.
• Solids and liquids can diffuse into liquids.
• The gases from the atmosphere diffuse and dissolve in water.
• Gases, especially oxygen and carbon dioxide, are essential for the survival of aquatic animals
  and plants.
• All living creatures need to breathe for survival.
• The aquatic animals can breathe under water due to the presence of dissolved oxygen in water.
• Solids, liquids and gases can diffuse into liquids.
• The rate of diffusion of liquids is higher than that of solids.
• In the liquid state, particles move freely and have greater space between each other as compared to particles in the solid state.
• Gases are highly compressible as compared to solids and liquids.
• Large volumes of a gas can be compressed into a small cylinder and transported easily, due ti its high compressibility.
• Due to high speed of particles and large space between them, gases show the property of diffusing very fast into other gases.
• 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 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 is an indication of the strength of the force of attraction between its particles.
• The melting point of ice is 273.16 K.
• The process of melting, that is, change of solid state into liquid state is also known as fusion.
• The forces of attraction between the particles are maximum in solids, intermediate in liquids and minimum in gases.
• The states of matter are inter-convertible. The state of matter can be changed by changing temperature or pressure.
• Sublimation is the change of gaseous state directly to solid state without going through liquid state, and vice versa.
• Boiling is a bulk phenomenon. Particles from the bulk (whole) of the liquid change into vapour state.
• The rate of evaporation depends upon the surface area exposed to the atmosphere, the temperature, the humidity and the wind speed.
• Evaporation causes cooling.
• Latent heat of vaporisation is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point.
• Latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point.
• Solid carbon dioxide is also known as dry ice.
• Phenomenon of changing of a liquid into vapours at any temperature below its boiling point is called evaporation.
• Humidity is the amount of water vapour present in air.
• The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point.