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PDF Solutions for NCERT Class 9 Science Chapter 1 - Learn about Matter in Our Surroundings


Class 9 Science Chapter 1: Matter in Our Surroundings




In this article, we will learn about the first chapter of Class 9 Science, which is about matter and its properties. We will understand what matter is, how it is classified, how it behaves in different states, and what factors affect its state. We will also look at some important questions and answers related to this chapter.




class 9 science chapter 1 question answer pdf download



Introduction




What is matter?




Matter is anything that has mass and occupies space. Everything that we can see, touch, smell, taste, or hear is made up of matter. For example, air, water, soil, plants, animals, rocks, metals, plastics, etc. are all examples of matter.


How is matter classified?




Matter can be classified in different ways based on its physical properties and chemical nature. One way to classify matter is based on its physical state: solid, liquid, or gas. Another way to classify matter is based on its composition: pure substance or mixture. A pure substance is a type of matter that has a fixed composition and cannot be separated into simpler substances by physical methods. For example, iron, copper, oxygen, water, etc. are pure substances. A mixture is a type of matter that contains two or more pure substances mixed together in any proportion and can be separated by physical methods. For example, air, sea water, milk, soil, etc. are mixtures.


Physical nature of matter




Characteristics of particles of matter




Matter is made up of very small particles that are too tiny to be seen with naked eyes. These particles have some characteristics that determine the physical nature and behaviour of matter. Some of these characteristics are:


  • Particles of matter have space between them: The particles of matter are not tightly packed but have some empty space between them. This space varies depending on the state and type of matter.



  • Particles of matter are constantly moving: The particles of matter are not stationary but have kinetic energy that makes them move randomly in all directions. This movement also varies depending on the state and temperature of matter.



  • Particles of matter attract each other: The particles of matter have some force of attraction between them that keeps them together. This force also varies depending on the state and distance between the particles.



  • All matter is composed of very small particles which can exist independently: The smallest unit of matter that can exist independently is called an atom. An atom is the building block of all matter and cannot be divided further by chemical methods. Atoms can combine with other atoms to form molecules, which are also particles of matter.



States of matter




Matter can exist in three main states: solid, liquid, and gas. These states differ in their shape, volume, density, compressibility, fluidity, movement, interparticle space, interparticle attraction, and rate of diffusion.


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class



PropertySolidLiquidGas


Shape and volumeFixed shape and volumeNo fixed shape but has volumeNeither definite shape nor volume


EnergyLowestMediumHighest


CompressibilityDifficultNearly difficultEasy


Arrangement of moleculesRegular and closely arrangedRandom and little sparsely arrangedRandom and more sparsely arranged</td Change of state of matter




Matter can change its state from one to another by changing the temperature or pressure. The change of state of matter is a physical change, which means that the identity and composition of the substance remain the same. The change of state of matter involves two processes: fusion and vaporization.


Fusion is the process of changing a solid into a liquid by heating it. For example, ice melts into water when heated. The temperature at which a solid changes into a liquid is called its melting point. Different solids have different melting points depending on the strength of their interparticle attraction.


Vaporization is the process of changing a liquid into a gas by heating it. For example, water boils into steam when heated. The temperature at which a liquid changes into a gas is called its boiling point. Different liquids have different boiling points depending on the strength of their interparticle attraction.


There are two types of vaporization: evaporation and boiling. Evaporation is the process of changing a liquid into a gas at any temperature below its boiling point. For example, water evaporates from the surface of oceans, lakes, and rivers. Boiling is the process of changing a liquid into a gas at its boiling point. For example, water boils in a kettle when heated.


Factors affecting the state of matter




Effect of temperature




Temperature is a measure of the average kinetic energy of the particles of matter. The higher the temperature, the faster the particles move and the more they collide with each other. This affects the state of matter in two ways:


  • Increasing the temperature increases the kinetic energy of the particles, which overcomes the interparticle attraction and makes them move apart. This causes the matter to expand and change its state from solid to liquid or from liquid to gas.



  • Decreasing the temperature decreases the kinetic energy of the particles, which increases the interparticle attraction and makes them move closer. This causes the matter to contract and change its state from gas to liquid or from liquid to solid.



Effect of pressure




Pressure is the force exerted by the particles of matter on a unit area. The higher the pressure, the more forceful the collisions between the particles are. This affects the state of matter in two ways:


  • Increasing the pressure decreases the interparticle space, which increases the interparticle attraction and makes them move closer. This causes the matter to contract and change its state from gas to liquid or from liquid to solid.



  • Decreasing the pressure increases the interparticle space, which decreases the interparticle attraction and makes them move apart. This causes the matter to expand and change its state from solid to liquid or from liquid to gas.



Evaporation




Evaporation is a type of vaporization that occurs at any temperature below the boiling point of a liquid. Evaporation is influenced by several factors, such as:


  • Surface area: The larger the surface area of a liquid, the more evaporation occurs.



  • Temperature: The higher the temperature of a liquid, the more evaporation occurs.



  • Humidity: The lower the humidity of air, the more evaporation occurs.



  • Wind speed: The higher the wind speed, the more evaporation occurs.



Evaporation causes cooling because it takes away heat energy from the liquid and leaves behind cooler molecules.


Conclusion




Summary of the chapter




In this chapter, we learned about matter and its properties. We learned that:


  • Matter is anything that has mass and occupies space.



Matter can be classified base


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