Long Questions Answers | Physical States of Matter

State and explain Boyle's law. Illustrate your answer with the help of a suitable diagram and graph.  

Boyle's law

This law states that

The volume of a given amount of a gas is inversely proportional to its pressure if the temperature of the gas is kept constant.

Explanation

In simple words, we can state Boyle's law as, if we take some gas in a container and apply pressure at constant temperature the gas molecules will occupy less volume and thus its volume will decrease with increasing pressure.

The mathematical form of Boyle's law

According to definition

P ∝ 1/V (Where P is pressure and V is the volume at constant temperature)

P = K x 1/V (K is the constant of proportionality)

Or P/V = K = Constant

If P1= Initial pressure, P2= Final pressure and V1 = Initial volume while V2 =Final volume then Boyle's law can be written as

P1 V1 = P2 V2 (at constant temperature)

Example: A 530dm3 sample of Hydrogen gas was collected in a container at 800mm of Hg pressure, at room temperature. What volume will the gas occupy at 400mm of Hg?

Given data

V1 = 530 dm3 P1 = 800 mm of Hg P2 = 400 mm of Hg

Required V2 = ?

Solution

As according to the Boyle’s law, we know that

P1 xV1 = P2 x V2

Dividing both sides by “P2”, we have

(P1 x V1) / P2 = (P2 x V2) / P2

Or V2 = (P1 x V1) / P2 …………..(i)

Putting the values in equation (i), we have

V2 = (800 mm of Hg x 530 dm3) / (400 mm of Hg)

V2 = (800 x 530 dm3) / (400 )

V2 = (424,000 dm3) / (400 )

V2 = 1060 dm3 Ans

State and explain Charles's law. Illustrate your answer with the help of a suitable diagram and graph.  

Charles's law

This law states that

The volume of a given amount of a gas is directly proportional to its temperature if the pressure of the gas is kept constant.

Explanation

In simple words, we can state Charles's law as, if we take some gas in a container and increase its temperature at constant pressure the gas molecules will occupy more volume and thus its volume will increase with increasing temperature.

The mathematical form of Charles's law

According to definition

V ∝ T (where T is temperature and V is the volume at constant pressure)

V = KT (K is the constant of proportionality)

V/T = K

If V1= Initial volume, V2= Final volume and T1= Initial temperature while T2 =Final temperature then Charles's law can be written as

V1/T1 = V2/T2 (at constant pressure)

Example: A 3 dm3 of air is heated from 300 K to 400 K at constant pressure. What is the volume of the gas at a higher temperature?

Given data

V1 = 3 dm3 , T1 = 300 K , T2 = 400 K

Required V2 =?

Solution

According to Charles’s law, we know that

V1 / T1 = V2 / T2

Or V2 = (V1 x T2) / T1 ……………(i)

Putting the values in eq (i), we have

V2 = (3 dm3 x 400 K) / (300 K)

Or V2 = 4 dm3 Ans

What are the typical properties of the Liquids?  

Typical properties of Liquids

Following are some of the typical properties of Liquids.

1. Definite Volume

Liquids have definite volumes because their molecules can't move freely.

2. Indefinite shape

Liquids have indefinite shapes and therefore they adopt the shape of the container in which they contain.

3. Mobility

Liquid molecules can move around but not as freely as gas molecules can.

4. Diffusion

Diffusion means mixing, so like gas molecules, liquids can also be mixed with another liquid.

5. Evaporation

The spontaneous change of a liquid into a gas state is called Evaporation.

Liquid molecules when heated up change into the gas state because their kinetic energy increases and they can move further apart from each other. However, the rate of evaporation depends on the strength of inter-molecular forces, temperature and area of the liquid.

6. Vapour pressure

The pressure applied by the vapours is called vapour pressure.

When liquids are heated their kinetic energy increases and they move above the container where they apply pressure. Vapour pressure occurs when there is evaporation. Some vapour turns back to a liquid state when cools down, this phenomenon is known as Condensation. The process of evaporation and condensation continues until the rate of evaporation becomes equal to the rate of condensation and equilibrium is developed.

Factors affecting vapour pressure

The following factors affect the vapour pressure of the liquids.

a. The nature of the liquid

If the intermolecular forces in the liquids are stronger, lesser will the vapour pressure of the liquids and vice versa.

Temperature With increasing temperature the kinetic energy of the liquids increases and thus its vapour pressure also increases.

b. Boiling point

The temperature at which the vapour pressure of the liquid becomes equal to the atmospheric pressure is called the Boiling point.

Explanation

When liquids are heated up, the kinetic energy of their molecules increases and due to this vapour pressure of the liquids increases. When this vapour pressure becomes equal to atmospheric pressure it starts boiling.

c. Freezing or Melting point

The temperature at which liquid freezes is called the Freezing or Melting point.

Define and explain the term Allotropy. Also, describe the allotropic forms of Carbon in detail.

Allotropy

The existence of an element in more than one crystalline form is called Allotropy.

Explanation

If one element exists in more than one form crystalline form we call it Allotropy and different forms are called Allotropic forms.

For example

Sulphur exists in two allotropic forms which are Rhombic Sulphur and Monoclinic Sulphur. Both forms are in equilibrium at the Transition temperature of 95.5 0C.

The temperature at which two allotropic forms are in equilibrium with each other is called Transition temperature.

Allotropic forms of Carbon

• Non-Crystalline form (Amorphous) form of Carbon is Coal, Coke, Charcoal and lampblack.
• A crystalline form of Carbon exists in three allotropic forms. These are Diamond, Graphite and Buckyballs. Their detail is given below as

1. Diamond

In Diamond, each Carbon atom is tetrahedrally (four-sided) bonded by four covalent bonds with four other Carbon atoms in cubic form. 
The following are the properties of Diamonds

• Hardness

Due to intense covalent bonds diamonds are very hard.

• High Melting point

Because of strong covalent bonds diamonds have high melting points.

• Bad conductor of electricity

Due to the tightness of bonds the valence electrons can’t flow with current so diamonds are bad conductor of electricity.

Uses of Diamond

1. As a gem      
2. For cutting and boring glass 
3. In jewellery.

2. Graphite

In Graphite Carbon atoms are hexagonally (six-sided) arranged in the form of a sheet. The attractive forces in Graphite are weak so they have opposite properties to that of diamonds i.e. Graphite is soft, lubricant and a good conductor of electricity.

Uses of graphite

1. As lubricant 
2. As electrode
3. In lead pencils

3. Buckyballs

Discovery of Buckyballs

Buckyballs were discovered in 1985 by a group of scientists.

Structure of Buckyballs

In Buckyballs, 40 to 100 Carbon atoms are arranged in cage-like structures called Bucky Balls. Carbon atoms in Buckyballs are packed in Pentagon (five-sided) and Hexagon (six-sided) structures and assume the shape of a football. 

Buckyballs are used as semiconductors, superconductors or as lubricants.

Uses of Buckyballs 

1. As lubricant. 
2. As semiconductor 
3. As superconductor