The intermolecular forces are weakest in:
- solids
- liquids
- gases
- both (1) and (2)
Answer
gases
Reason — The intermolecular forces are weakest in gases. In solids, intermolecular forces are the strongest because particles are tightly held together. In liquids, intermolecular forces are weaker than in solids but stronger than in gases.
The intermolecular spaces are the least in:
- aluminium
- water
- oxygen
- carbon dioxide
Answer
aluminium
Reason — Aluminium is a solid, so its particles are closely packed and the intermolecular spaces are very small. In water, intermolecular spaces are more than in solids but less than in gases. Oxygen and carbon dioxide are gases, so they have very large intermolecular spaces.
The state of matter which has a definite volume but takes the shape of a container is:
- solids
- liquids
- gases
- none
Answer
liquids
Reason — Liquids have a definite volume but no definite shape. They take the shape of the container in which they are kept. Solids have a definite shape and definite volume. Gases have neither a definite shape nor a definite volume.
Which of the following is transparent?
- Diamond
- Graphite
- Wood
- Coal
Answer
Diamond
Reason — Diamond is transparent as it allows light to pass through it. Graphite, wood and coal are opaque.
The process by which a solid changes directly from the solid state to the gaseous state is called:
- diffusion
- sublimation
- evaporation
- melting
Answer
sublimation
Reason — Sublimation is the process by which a substance directly changes from its solid state to its gaseous state without passing through the liquid state. Diffusion is the intermixing of particles. Evaporation is the change of a liquid into vapour. Melting is the change of a solid into a liquid.
Assertion (A) — Matter exists in three states, i.e. solids, liquids and gases.
Reason (R) — All matter can change from one state to another on changing temperature and pressure.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Answer
A is true but R is false.
Reason — A is true as matter exists in three states, i.e. solids, liquids and gases due to differences in particle arrangement and forces.
R is false as not all kinds of matter can change from one state to another on changing temperature and pressure. Many substances decompose or char on heating instead of simply changing their state.
Therefore, A is true but R is false is the correct option.
Assertion (A) — When a gas is cooled, the intermolecular gaps decrease.
Reason (R) — The kinetic energy of the gaseous particles decrease upon cooling.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Answer
Both A and R are true and R is the correct explanation of A.
Reason — A is true because when a gas is cooled, its particles lose energy, move more slowly and come closer. Hence, the intermolecular gaps decrease. R is true because the kinetic energy of gaseous particles decreases on cooling.
Therefore, Both A and R are true and R is the correct explanation of A is the correct option.
Assertion (A) — Most of the liquids have their own shape.
Reason (R) — Liquids can flow from a higher to lower level.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Answer
A is false but R is true.
Reason — A is false as liquids do not have a fixed shape. They take the shape of the container they are placed in. Only volume is fixed, not shape.
R is true as liquids can flow easily due to weaker intermolecular forces. This is why they move from higher level to lower level.
Therefore, A is false but R is true is the correct option.
Assertion (A) — Particles of matter are always in random motion.
Reason (R) — Particles of matter possess kinetic energy.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Answer
Both A and R are true and R is the correct explanation of A.
Reason — A is true because particles of matter are always in random motion. R is true because particles possess kinetic energy, and due to this energy, they keep moving continuously.
Therefore, Both A and R are true and R is the correct explanation of A is the correct option.
Assertion (A) — A piece of wood is a hard solid, while that of chalk is a soft solid.
Reason (R) — In solids, the intermolecular forces of attraction are very strong.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Answer
Both A and R are true but R is not the correct explanation of A.
Reason — A is true because wood is a hard solid, while chalk is a soft solid and can be broken easily. R is true because intermolecular forces of attraction are strong in solids. However, R does not explain why wood is hard while chalk is soft; this difference is due to stronger intermolecular attraction in wood than in chalk.
Therefore, Both A and R are true but R is not the correct explanation of A is the correct option.
Fill in the blanks:
(a) Air is a matter because it has ............... and ............... and it can be ............... .
(b) The molecules are made up of ............... .
(c) The quantity of matter in an object is called its ............... .
(d) The state of matter with definite volume and definite shape is called ............... .
(e) The substances which can flow are called ............... .
Answer
(a) mass, volume, felt
(b) atoms
(c) mass
(d) solid
(e) fluids
Write whether the following statements are true or false.
(a) Solids can diffuse very fast.
(b) The quantity of matter in an object is called volume.
(c) Atoms combine to form molecules.
(d) Particles of matter can move because they possess kinetic energy.
(e) When a liquid is heated, it solidifies.
Answer
(a) False
Correct Statement — Gases can diffuse very fast.
(b) False
Correct Statement — The quantity of matter in an object is called mass.
(c) True
(d) True
(e) False
Correct Statement — When a liquid is heated, it changes into vapour.
Match the following:
| Column A | Column B |
|---|---|
| (a) Fluids | (i) space between the molecules |
| (b) Melting point | (ii) change of state from gas to liquid |
| (c) Atoms | (iii) substances which can flow |
| (d) Intermolecular space | (iv) the smallest particles of matter |
| (e) Condensation | (v) the temperature at which a solid changes to a liquid |
Answer
| Column A | Column B |
|---|---|
| (a) Fluids | (iii) substances which can flow |
| (b) Melting point | (v) the temperature at which a solid changes to a liquid |
| (c) Atoms | (iv) the smallest particles of matter |
| (d) Intermolecular space | (i) space between the molecules |
| (e) Condensation | (ii) change of state from gas to liquid |
Classify the following into solid, liquid and gas:
Coal, kerosene, wood, oxygen, sugar, blood, water vapour, milk, wax.
Answer
| Solid | Liquid | Gas |
|---|---|---|
| Coal | Kerosene | Oxygen |
| Wood | Blood | Water vapour |
| Sugar | Milk | |
| Wax |
Give appropriate terms for the following:
(a) The change of a solid into liquid.
(b) The force of attraction between the molecules of matter.
(c) The particles of matter which may or may not have independent existence.
(d) The process due to which a solid directly changes into its vapours.
(e) The change of vapour into a liquid.
Answer
(a) Melting
(b) Intermolecular force of attraction
(c) Atoms
(d) Sublimation
(e) Condensation
Give two examples for the following:
(a) substances which can flow
(b) substances which can sublime
(c) substances which can diffuse.
Answer
(a) Water, Alcohol
(b) Camphor, Naphthalene
(c) Oxygen, Nitrogen
Define matter.
Answer
Matter is anything that has mass, occupies space and can be perceived by our senses.
Differentiate between an atom and a molecule.
Answer
| Atom | Molecule |
|---|---|
| An atom is the smallest possible unit of matter that exhibits all the properties of that matter and may or may not have independent existence. | A molecule is the smallest unit of matter which exhibits all the properties of that kind of matter and also has an independent existence. |
| An atom is smaller than a molecule. | A molecule is bigger than an atom as it is made up of two or more atoms. |
What do you understand by:
(a) Intermolecular force of attraction,
(b) Intermolecular space?
Answer
(a) There exists a force of attraction between the particles or molecules of matter, which holds them together. This is known as intermolecular force of attraction.
(b) Particles of matter have space between them. This space is called interparticular or intermolecular space.
Why are liquids and gases called as fluids?
Answer
The substances which can flow are known as fluids. Liquids flow from higher to lower level and gases flow in all directions, so they are called as fluids.
Define:
(a) Solid
(b) Liquid
(c) Gas
Give two examples of each type.
Answer
(a) Solid — A solid is a state of matter which has a definite shape and a definite volume. Examples: gold, wood.
(b) Liquid — A liquid is a state of matter which has a definite volume but no definite shape. Examples: water, alcohol.
(c) Gas — A gas is a state of matter which has neither a definite shape nor a definite volume. Examples: hydrogen, oxygen.
Write your observations and conclusions for the following:
(a) A few marbles are put in a glass half filled with water.
(b) Ice is kept at room temperature.
Answer
(a) Observation — When a few marbles are put in a glass half-filled with water, the water level rises.
Conclusion — Marbles occupy space. This shows that matter occupies space.
(b) Observation — When ice is kept at room temperature, it changes into water.
Conclusion — Ice absorbs heat from the surroundings and melts. This shows that a solid can change into a liquid on heating.
State three main characteristics of the particles of matter.
Answer
The three main characteristics of the particles of matter are:
- Particles of matter have space between them and this space is called inter-particular or inter-molecular space.
- Particles of matter are always in random motion.
- Particles of matter attract each other.
(a) Define interconversion of states of matter.
(b) Why do solids, liquids and gases differ in their physical state?
(c) Under what conditions do solids, liquids and gases change their state?
Answer
(a) Interconversion of states of matter is the process by which matter changes from one state to another and back to its original state without any change in its chemical composition, when conditions are changed.
(b) Solids, liquids and gases differ in their physical state due to differences in intermolecular space, intermolecular force of attraction and the movement of their particles.
In solids, molecules are closely packed and the force of attraction is very strong. In liquids, molecules are less tightly packed and the force of attraction is weaker than in solids. In gases, molecules are far apart and the force of attraction is very weak.
(c) Solids, liquids and gases change their state by change in temperature or by applying pressure.
Name the processes marked as A, B, C, D, E, and F.
Answer
A → Melting
B → Evaporation
C → Condensation
D → Freezing / Solidification
E → Sublimation
F → Deposition
Give reasons:
When a stone is dipped in a glass containing some water, the level of water rises but when a spoon of sugar is added to it and stirred, the water level does not rise.
Answer
When a stone is dipped in a glass containing some water, the water level rises because the stone is a bigger object and cannot be dissolved and adjusted between the intermolecular spaces of water.
When a spoon of sugar is added to water and stirred, the water level does not rise because sugar particles are smaller and get adjusted between the intermolecular spaces present in water molecules.
Give reasons:
A drop of ink added to water in a glass turns the whole water blue.
Answer
A drop of ink added to water in a glass turns the whole water blue because the water and ink particles are in continuous random motion. Due to this motion, the blue coloured particles of ink spread throughout the water and give it a blue colour.
Sapna was making an orange flavoured drink. She poured 3-4 teaspoons of concentrated orange juice into a glass. She then added water until the glass was full and stirred it slowly.
(a) Explain how the orange juice spread into water.
(b) What is the effect of stirring?
(c) What is this intermixing of particles called? Name the type of substances which show this phenomenon the fastest.
(d) "There is no more movement in the liquid in the glass once the orange colour of the juice has stopped spreading."
Is this statement correct? Justify your answer.
Answer
(a) The particles of orange juice and water are constantly moving. Due to this random motion, the orange juice particles mix and spread throughout the water.
(b) Stirring increases the speed of mixing. It helps the orange juice particles spread faster in water.
(c) The intermixing of particles is called diffusion. Gases show diffusion the fastest.
(d) The statement is incorrect. Even when the orange colour stops spreading, the particles in the liquid are still moving continuously. The movement becomes uniform in all directions, so no visible change is seen.