Q1: What is matter? (a) Anything that has mass and occupies space (b) Only solid substances (c) Only things we can see with our eyes (d) Energy in different forms
Solution:
Ans: (a) Explanation: Matter is defined as anything that takes up space and has mass, existing as solids, liquids, or gases all around us.
Q2: What is the size of a molecule? (a) 10-5 metres (b) 10-10 metres (c) 10-15 metres (d) 10-20 metres
Solution:
Ans: (b) Explanation: Molecules are extremely small, about 10-10 metres in size, which is why they cannot be seen with our eyes or even ordinary microscopes.
Q3: Why do liquids have a fixed volume but no fixed shape? (a) Because molecules are completely free to move anywhere (b) Because inter-molecular forces are strong enough to keep molecules within boundaries but allow flow (c) Because molecules do not move at all (d) Because there is no space between molecules
Solution:
Ans: (b) Explanation: Liquids have inter-molecular forces that keep molecules within the liquid's boundaries, giving fixed volume, but are weak enough to allow flow, giving no fixed shape.
Q4: Which factor does NOT affect the rate of evaporation? (a) Temperature of the liquid (b) Area of exposed surface (c) Colour of the liquid (d) Flow of air above the liquid
Solution:
Ans: (c) Explanation: The rate of evaporation depends on temperature, surface area, nature of liquid, air flow, and humidity, but not on the colour of the liquid.
Q5: What happens when a solid is heated at its melting point? (a) Temperature continues to increase steadily (b) Heat is absorbed but temperature remains constant (c) The solid immediately becomes a gas (d) The molecules stop moving completely
Solution:
Ans: (b) Explanation: At the melting point, absorbed heat is used to overcome inter-molecular forces rather than increasing temperature, known as latent heat of fusion.
Fill in the Blanks
Q1: Matter is made up of tiny particles called _____.
Solution:
Ans: molecules
Q2: The space between molecules is called _____ space.
Solution:
Ans: inter-molecular
Q3: The process of a solid directly changing into a gas is called _____.
Solution:
Ans: sublimation
Q4: The force of attraction between molecules of the same substance is called the force of _____.
Solution:
Ans: cohesion
Q5: The temperature at which a liquid turns into a solid is called the _____ point.
Solution:
Ans: freezing
True or False
Q1: Molecules can be seen with our eyes because they are very large.
Solution:
Ans: False Explanation: Molecules are about 10-10 metres in size and cannot be seen with our eyes due to their extremely small size.
Q2: In solids, the inter-molecular space is very small and molecules are packed closely together.
Solution:
Ans: True Explanation: Solids have the least inter-molecular space with molecules very close together, resulting in their rigid structure and fixed shape.
Q3: Evaporation happens only at the boiling point of a liquid.
Solution:
Ans: False Explanation: Evaporation occurs at all temperatures from the surface of a liquid, while boiling happens only at a fixed boiling point.
Q4: The melting point and freezing point of a substance are the same.
Solution:
Ans: True Explanation: For any substance, the temperature at which it melts is exactly the same as the temperature at which it freezes.
Q5: Gas molecules have very high kinetic energy and move freely in all directions.
Solution:
Ans: True Explanation: Gases have very high kinetic energy allowing molecules to move freely and randomly in all available space without fixed positions.
Match the Following
Solution:
Ans:
1 - D: Melting is the process where a solid changes into a liquid by absorbing heat at its melting point.
2 - C: Condensation is the process where a gas or vapour turns back into a liquid by releasing heat.
3 - E: Sublimation occurs when a solid directly changes into a gas without becoming a liquid, like camphor or naphthalene.
4 - B: Force of cohesion is the attraction between molecules of the same substance, important for properties like surface tension.
5 - A: Kinetic energy is the energy molecules possess due to their constant motion, varying in solids, liquids, and gases.
Short Answer Questions
Q1: What are the three main characteristics of molecules that determine the state of matter?
Solution:
Ans: The three characteristics are inter-molecular space, inter-molecular force of attraction, and kinetic energy from molecular motion. Solids have minimal space, strong attraction, and low kinetic energy. Liquids have moderate space and forces with higher kinetic energy. Gases have large space, weak forces, and very high kinetic energy allowing free movement.
Q2: Explain why evaporation produces a cooling effect.
Solution:
Ans: During evaporation, liquid molecules gain energy to escape as gas. This energy is taken from surroundings as heat. The liquid absorbs heat from nearby surfaces, causing them to cool down. For example, when sweat evaporates, it takes heat from our body, making us feel cooler and helping maintain body temperature.
Q3: What are the main differences between evaporation and boiling?
Solution:
Ans: Evaporation is a slow process occurring at all temperatures from the liquid surface, producing cooling. Boiling is fast, occurring only at boiling point throughout the liquid without cooling effect. Evaporation depends on temperature, surface area, liquid nature, air flow, and humidity. Boiling happens at fixed temperature for each substance.
Q4: Describe the molecular model of gases and explain their properties.
Solution:
Ans: Gas molecules are very small and far apart with large inter-molecular spaces. Inter-molecular forces are very weak, allowing free movement in all available space. Gas molecules have very high kinetic energy and move randomly in all directions. This is why gases have no definite shape or volume and spread to fill their container completely.
Q5: Give three applications of evaporation in daily life.
Solution:
Ans: Water cools in earthen pots as surface evaporation takes heat from inside water. Wet cloths cool fever patients as water evaporation removes heat. Tea in a saucer cools faster due to larger surface area increasing evaporation. Cotton clothes help sweat evaporate in summer, cooling our bodies and maintaining temperature.
Ans. Matter is anything that has mass and occupies space. It is composed of particles and can exist in various states, such as solid, liquid, or gas.
2. What are the three states of matter?
Ans. The three states of matter are solid, liquid, and gas. Solids have a definite shape and volume, liquids have a definite volume but take the shape of their container, and gases have neither a definite shape nor a definite volume.
3. How does temperature affect the state of matter?
Ans. Temperature affects the state of matter by providing energy to the particles. Increasing temperature typically causes solids to melt into liquids, and liquids to evaporate into gases. Conversely, decreasing temperature can cause gases to condense into liquids and liquids to freeze into solids.
4. What is the difference between physical and chemical changes in matter?
Ans. Physical changes affect the form of a substance but do not alter its chemical composition, such as melting or boiling. Chemical changes, on the other hand, result in the formation of new substances, like the rusting of iron or the combustion of wood.
5. What is the role of atoms in matter?
Ans. Atoms are the basic building blocks of matter. They combine in various ways to form molecules and compounds, which make up all substances in the universe. The arrangement and bonding of atoms determine the properties and behaviour of the matter.
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