Matter

The process in which a substance in solid state directly changes into gaseous state is called as:

1. Condensation
2. Sublimation
3. Deposition
4. Vaporisation

Answer

Sublimation

Reason — Sublimation is the process in which some substances that directly change from the solid state to the gaseous state without passing through the liquid state. Such substances are called sublimable substances.

The three states of matter i.e. solid, liquid and gas exist due to :

1. Random motion of molecules in a substance
2. Intermolecular space
3. Intermolecular force of attraction
4. All of the above

Answer

All of the above

Reason — The three states of matter (solid, liquid, and gas) are determined by the random motion of molecules, the intermolecular space, and the intermolecular forces of attraction. In solids, molecules are tightly packed with strong forces and limited movement; in liquids, the molecules are less tightly packed, with weaker forces allowing them to move past each other; in gases, the molecules are far apart with very weak forces, allowing free movement.

The intermolecular force of attraction is the strongest in:

1. solids
2. liquids
3. gases
4. none of the above

Answer

solids

Reason — In solids, the intermolecular forces of attraction are the strongest, which is why the molecules are packed tightly together.

Which of the following substances has the largest intermolecular spaces?

1. A piece of iron metal
2. A glass of water
3. A spoon of common salt
4. A balloon filled with hydrogen gas

Answer

A balloon filled with hydrogen gas

Reason — Gases have the largest intermolecular spaces compared to solids and liquids. In a gas like hydrogen, the molecules are far apart and move freely, resulting in much larger intermolecular spaces.

The type of energy possessed by a moving body is called as:

1. Electrical energy
2. Light energy
3. Heat energy
4. Kinetic energy

Answer

Kinetic energy

Reason — The energy possessed by a body due to its motion is called kinetic energy.

What happens to the kinetic energy when a solid substance is heated?

1. Increases
2. Decreases
3. No change
4. May increase or decrease

Answer

Increases

Reason — When a solid substance is heated, its molecules gain more energy and start to move faster. This increase in the motion of molecules leads to an increase in their kinetic energy. The higher the temperature, the greater the kinetic energy of the particles.

Assertion (A): Matter exists in three states; i.e. solids, liquids and gases.

Reason (R): The intermolecular forces of attraction and intermolecular spaces are different in different kinds of matter.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true and R is the correct explanation of A.

Explanation — The three states of matter exist because the intermolecular forces and spaces between particles vary — strong intermolecular forces and lesser intermolecular space in solids, weaker intermolecular forces and more intermolecular space in liquids, and very weak intermolecular forces with large intermolecular spaces in gases.

Assertion (A): Liquid molecules can move freely and are able to occupy the whole space available to them.

Reason (R): The molecules of liquids have larger intermolecular spaces and weaker intermolecular forces of attraction than those in solids.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

A is false but R is true.

Explanation — Liquids cannot occupy the whole space available to them as they have a fixed volume, but they flow and take the shape of the container into which they are poured.

Assertion (A): Naphthalene balls become smaller with the passage of time, as they sublime.

Reason (R): Naphthalene balls sublime, as such solids have stronger intermolecular forces of attraction in comparison to other solids.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

A is true but R is false.

Explanation — Sublimable solids have weaker intermolecular forces of attraction in comparison to other solids. On heating, they acquire the kinetic energy of their vapour phase faster, and directly converts to gaseous state without entering the liquid state.

Assertion (A): Conversion of a substance in solid state to its liquid state is called melting.

Reason (R): On heating, the kinetic energy of solid molecules increases.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true but R is not the correct explanation of A.

Explanation — The process by which a substance changes from solid to liquid is called melting or fusion. On heating, the kinetic energy of solid molecules increases, causing them to vibrate more. This increase in motion weakens the intermolecular forces of attraction, allowing the molecules to move more freely and thus change into the liquid state.

Assertion (A): Solids can be hardly compressed by applying pressure.

Reason (R): The molecules in solids are closely packed.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

Both A and R are true and R is the correct explanation of A.

Explanation — Solids cannot be compressed easily because their molecules are tightly packed with very little intermolecular space. This close packing leaves no room for the particles to be pushed closer together, making solids rigid and incompressible.

Fill in the blanks:

(a) The change of a solid into a liquid is called ............... .

(b) The process in which a solid directly changes into gas is called ............... .

(c) The change of water vapour into water is called ............... .

(d) The temperature at which a liquid starts changing into its vapour state is ............... .

(e) A gas can be changed into a liquid and then into solid by ............... its pressure and cooling.

(f) LPG cylinders contain cooking gas in ............... state at high pressure.

(g) In a chemical reaction, the total mass of the reactants is ............... to the total mass of the products.

Answer

(a) Melting

(b) Sublimation

(c) Condensation

(d) Boiling point

(e) increasing

(f) liquid

(g) equal

Write whether the following statements are true or false.

(a) Matter can be created or destroyed during a chemical reaction.

(b) When a substance changes its state, its mass is also changed.

(c) In solids, the molecules can only vibrate about their mean positions. They are not free to move.

(d) In liquids, the kinetic energy of molecules is less than that of solids.

(e) In gases, the intermolecular forces of attraction are negligible.

Answer

(a) False
Correct Statement — Matter can neither be created nor be destroyed in a chemical reaction.

(b) False
Correct Statement — When a substance changes its state, its total mass stays the same.

(c) True

(d) False
Correct Statement — In liquids, the kinetic energy of molecules is more than that of solids.

(e) True

Match the following:

Answer

Name the following:

(a) The substances which can flow.

(b) The intermixing of two or more substances due to their motion.

(c) The force of attraction between the particles of a substance.

(d) The substances which have a definite shape and volume.

(e) The state of matter which is highly compressible.

(f) The temperature at which a solid starts changing into a liquid.

(g) The change of vapour of a substance directly into a solid on cooling.

Answer

(a) Fluids

(b) Diffusion

(c) Interparticle or intermolecular force of attraction

(d) Solids

(e) Gas

(f) Melting Point

(g) Deposition

Give two examples for each of the following:

(a) The substances which can sublime.

(b) The substances which do not change their state on heating.

(c) The substances which can flow.

Answer

(a) Camphor, Ammonium Chloride.

(b) Paper, Wood.

(c) Water, Air.

Define the following terms:

(a) Matter

(b) Intermolecular force of attraction

(c) Diffusion

(d) Brownian motion

(e) Kinetic energy

Answer

(a) Matter — Matter is anything that has mass, occupies space and can be perceived by our senses.

(b) Intermolecular force of attraction — A force of attraction that exists between the particles of matter which holds them together is known as intermolecular force of attraction.

(c) Diffusion — The intermixing of two or more substances due to the motion of their particles in order to get a uniform mixture is called diffusion.

(d) Brownian motion — The zig-zag, random motion of suspended particles on the surface of a liquid or in air is called Brownian motion.

(e) Kinetic energy — The energy possessed by a body due to its motion is called kinetic energy.

Give reasons:

A gas can fill the whole vessel in which it is enclosed.

Answer

The particles of gases lie far apart from each other and the intermolecular spaces are therefore very large. The intermolecular forces of attraction are so weak that the particles are free to move and they have high kinetic energy, so they fill the whole vessel in which it is enclosed.

Give reasons:

Solids cannot be compressed.

Answer

In solids, the particles are closely packed. There is a strong force of attraction between the particles and the intermolecular space is almost negligible. The molecules are therefore not free to move. They only vibrate about their mean positions. This makes solids difficult to compress.

Give reasons:

Liquids can flow.

Answer

In liquids the molecules are loosely packed and the intermolecular forces of attraction is not so strong as solids. The intermolecular space is larger and kinetic energy is more as compared to solids. The particles can move freely and randomly which makes the liquids to flow.

Give reasons:

When magnesium is burnt in air, there is an increase in mass after the reaction.

Answer

When magnesium is burnt in air, it forms magnesium oxide. The mass of magnesium oxide is found to be more than the mass of magnesium because the mass of oxygen used is not taken into consideration. If that is considered the total mass of the reactants and the products are found to be almost equal.

2Mg + O₂ $\xrightarrow{\text{heat}}$ 2MgO

Give reasons:

When sodium chloride is added to a definite volume of water and stirred well, a solution is formed, but there is no increase in the level of water.

Answer

There are some intermolecular spaces between the particles of water. When sodium chloride is added into water and stirred, the particles of sodium chloride occupy the intermolecular spaces present in water particles and gets accommodated so there is no increase in the level of water.

Give reasons:

A piece of chalk can be broken easily into smaller pieces but a coal piece cannot be broken easily.

Answer

The magnitude of intermolecular force of attraction between the molecules of coal is much higher than that between the molecules of chalk. Hence, a piece of chalk can be broken easily into smaller pieces while a coal piece cannot be broken easily.

State your observation when :

(a) A gas jar which appears empty is inverted over a gas jar containing Bromine vapours.

(b) Solid ammonium chloride is heated.

(c) Vinegar is added to baking soda.

Answer

(a) Reddish brown vapours of bromine spread out from the gas jar into the empty jar, due to diffusion.

(b) On heating, solid ammonium chloride sublimes directly changing into white vapour, without changing into its liquid state. The vapour rises and solidifies on the upper cooler part of the test tube.

(c) When vinegar is added to baking soda, a strong effervescence or fizz sound occurs indicating the formation of carbon dioxide gas.

Give word equations for the following reactions:

(a) Barium chloride solution is added to sodium sulphate solution.

(b) Vinegar is added to baking soda.

(c) Magnesium burns in oxygen.

Answer

(a) Barium chloride + Sodium sulphate → Barium sulphate + Sodium chloride

(b) Acetic acid + Sodium bicarbonate → Carbon dioxide + Water + Sodium acetate

(c) Magnesium + Oxygen (Air) → Magnesium oxide

Some of the properties of solids, liquids and gases are listed ahead.

Separate these properties for the three states of matter.

Definite volume, least closely packed, can flow downwards, highly compressible, highly rigid, diffuse slowly.

Answer

Arrange the following:

(a) Solids, liquids and gases in increasing order of the constant motion of their particles.

(b) Copper metal, water vapour and milk in decreasing order of their intermolecular forces of attraction.

Answer

(a) Solids < Liquids < Gases.

(b) Copper metal > Milk > Water vapour

What are the three states of matter? Define each of them and give two examples of each.

Answer

The three states of matter are solids, liquids and gases.

Solids — A solid has a definite shape and a definite volume. The two examples are iron, wood.

Liquids — A liquid has a definite volume but no definite shape. The two examples are water, alcohol.

Gases — A gas has neither a definite shape nor a definite volume. The two examples are hydrogen, oxygen.

What is meant by interconversion of matter?

Answer

The phenomenon of change of one state of matter into another and then back to the original state without any change in its chemical composition is called interconversion of the states of matter.

State two factors responsible for the change of state of matter.

Answer

The two factors responsible for the change of state of matter are:

1. Change in temperature
2. Change in pressure.

What happens to intermolecular forces of attraction when a solid substance is heated?

Answer

When a substance in solid state is heated, its constituent particles gain kinetic energy and start vibrating more vigorously. Eventually, a stage is reached at which particles gain enough energy to overcome the forces of attraction between them and they start moving, thus changing into liquid state from the solid state.

State the main postulates of kinetic theory of matter.

Answer

The main postulates of kinetic theory of matter are:

1. Matter is composed of very small particles called atoms and molecules.
2. The constituent particles of a kind of matter are identical in all respects.
3. These particles have spaces or gaps between them which are known as inter-particular or inter-molecular spaces.
4. A force of attraction exists between the particles of matter which holds them together known as interparticular or intermolecular force of attraction.
5. Particles of matter are always in a state of random motion and possess kinetic energy which increases with an increase in temperature and vice-versa.

What happens to water if:

(a) it is kept in a deep freezer?

(b) it is heated?

Explain the change of state of water for the above two conditions with the help of kinetic theory.

Answer

(a) When water is kept in a deep freezer, it gets cooled and changes into ice at 0°C.

Water $\xrightarrow[\text{freeze}]{\text{deep}}$ ice (0°C)

Phenomenon of change of state of water — When water is kept in deep freezer, it changes into ice at 0°C. This is because when cooling is done, the kinetic energy decreases. Thus, the spaces between the particles decrease and the forces of attraction increase. This also affects the movements of particles, and at 0°C water starts converting into its solid state, i.e. ice.

(b) When water is heated it changes into steam at 100°C.

Water $\xrightarrow{\text{heating}}$ steam (100°C)

Phenomenon of change of state of water — On heating water, it changes into steam at 100°C. When heat is provided to water, its constituent particles gain more kinetic energy and start moving even more vigorously. The forces of attraction become almost negligible, increasing the intermolecular spaces and ultimately water changes into steam at 100°C.

State the law of conservation of mass.

Answer

The law of conservation of mass states that matter can neither be created nor be destroyed in a chemical reaction. Only it can be changed from one form to another during the reaction process.

What change occurs in the mass of a solid when it is heated to convert into a liquid?

Answer

There is no change in the mass of the solid even when its state changes into a liquid.

What do you observe when barium chloride solution is mixed with sodium sulphate solution ?
What difference is observed in the mass of reactants and products in the above reaction ?

Answer

When barium chloride solution is mixed with sodium sulphate solution, a white insoluble precipitate of barium sulphate is formed along with a solution of sodium chloride.

BaCl₂ + Na₂SO₄ ⟶ 2NaCl + BaSO₄↓

On weighing the apparatus before and after the reactions it is found that:
Total mass of the apparatus + reactants = Total mass of the apparatus + products

Hence, in a chemical reaction, the total mass of the reactants is equal to the total mass of the products. This observation verifies the law of conservation of mass.