# FBISE 9th Class Chemistry Chapter 5 Physical States of Matter Short Questions Answers

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Class/Subject: 9th Class Chemistry

Chapter Name: Physical States of Matter

Board: Federal  Board

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## FBISE 9th Class Chemistry Chapter 5 Physical States of Matter Short Questions Answers

Define gas law?

The relationship that expresses the influence of one variable on another with the two variable constants is called gas law.

State Boyle’s law.

Boyle’s law states that the value of a fixed amount of a gas at a given temperature is inversely proportional to the applied pressure.
Mathematically form of Boyle’s law:
p α 1/v
p = 1/v
V x P = constant

Briefly explain Charles’s law:

The law states that the volume of a given mass of a gas varies directly with the absolute temperature at constant pressure.
Mathematically form of Charles’s law:
V α T
V = constant x T
V/T = constant
This relationship is known as Charles’s law.
Since, ratio of V/T is constant,
V/T = constant
V = T x constant
V α T

Define distillation?

A process called distillation is used to purify liquids. Distillation is the process in which a liquid is heated to vaporize it and the vapors are cooled to condense them back to the liquid in a different container.

Define Melting point?

The temperature at which a solid turns into a liquid is called the melting point.

Define Freezing point?

On cooling the liquid freezes. Thus, the freezes of a liquid are the reserve of melting. The temperature at which a liquid changes into the solids is called the freezing point.

Define Sublimation?

Some solids on heating change to vapors without passing through the liquid state. This process is called sublimation.

What is allotropy?

The different forms of an element in the same physical state and phase are called allotropic forms or allotropes.

Define Diffusion?

Diffusion is the movement of molecules from a higher to lower concentration is called diffusion.

Define Effusion?

The escape of gas molecules through a hole one after the other without collisions is called an effusion.

Define Evaporation?

The conversion of a liquid to a gas or vapor at all temperatures is called vaporization or evaporation.

Define atmospheric pressure?

It is defined as the pressure exerted by a mercury column of 760mm height of sea level. It is sufficient pressure to support a column of is mercury in height at sea level.

What do you mean by Pascal? How many Pascal is equal to 1atm?

Pascal is the SI unit of Pressure
One Pascal = 1 Nm2

What is an absolute temperature scale?

Lord Kelvin introduced an absolute temperature scale or Kelvin scale. This scale of temperature starts from 0°K or -273.15°C which is given the name of absolute zero. It is the temperature at which an ideal gas would have zero volume.

Define Condensation?

The process of moving the molecules from the vapors phase back into the liquid phase is called condensation.

What do you mean by dynamic equilibrium?

When the rate of evaporation becomes equal to the rate of condensation at the stage, the number of molecules evaporating will be equal to the number of molecules coming back to liquid. This state is called dynamic equilibrium.

Define amorphous solids?

Amorphous solids mean shapeless solid in which the particles are not regularly arranged or their regular shapes are destroyed.

Define crystalline solids?

Solids in which particles are arranged in a definite three-dimensional pattern are called crystalline solids.

Define transition temperature?

The temperature at which one allotrope changes into another is called transition temperature.

Why pressure cooker saves time in the kitchen?

The pressure cooker is equipped with a value that controls the pressure inside the pot. This value generally exerts a pressure of 2 atm. Therefore, the value does not allow water vapors to escape until the pressure inside the pot reaches 2 atm. Because the vapor pressure of water becomes 2 atm when the temperature reaches 120°C. So, water boils at 120°C in a pressure cooker. That is why mountaineers carry with them a pressure cooker to cook the food quickly.

Define Pressure?

Force exerted by a gas on the unit area of a container is called its pressure.

Why gases are compressible?

Gases are highly compressible. This is due to the presence of large empty spaces between the gas molecules. On applying pressure distances between the gas molecules decreases, therefore, its volume decreases.

Briefly describe the density of gases?

Gases have relatively low densities under normal conditions. This is because the molecules are much further apart in the gas. When a gas is cooled its density increases because its volume decreases.

How a sample of a gas can be characterized by variables?

i. Pressure (P)
ii. Volume (V)
iii. Temperature (T)
iv. The number of moles of gas (n)

Does evaporation take place at all temperatures?

The molecules whose kinetic energies are greater than the average kinetic energy of the molecules, escape from the surface of the liquid. If the temperature of the liquid is increased, the rate of evaporation also increases. Anyhow, evaporation takes place at all temperatures and only the rate differs.

Does vapor pressure depend upon the nature of a liquid?

Yes, vapor pressure depends upon the nature of a liquid. The vapor pressure of a liquid decreases when intermolecular forces increase.

Does boiling point depend upon external pressure?

Yes, the boiling point depends upon external pressure. The boiling point of s liquid decreases with the decrease in external pressure.

Briefly explain the allotropic form of sulphur?

Sulphur consists of molecules that contain eight atoms, S, Sulphur also exists in several crystallines and an amorphous form. Rhombic and monoclinic forms are important crystalline allotropes. Plastic sulphur is an amorphous form.

Describe the mobility of gas molecules?

Gas molecules are always in a state of continuous motion. They can move from one place to another because gas molecules possess very high kinetic energy.

Why the rate of diffusion of gases is rapid than that of liquid?

Because gas molecules have sufficient intermolecular forces as compare to liquid. So the rate of diffusion of gases is rapid than that of liquid.

Can you make water boils at 70°C?

Yes, when the pressure of the atmosphere is 1atm or 101,325 kPa water boils at 100°C at sea level. This is because at this temperature vapor pressure of water is 1atm or 101,325 kPa. At Mount Everest, at about 8850m above sea level, atmospheric pressure is only 34 kPa. So, water boils at this height above sea level when its vapor pressure is 34 kPa at 70°C. So, water boils at 70°C.

At what temperature ethanol will boil when the atmospheric pressure is 51 kPa?

At 101.3 kPa pressure, Ethanol boils = 78°C
At kPa pressure, Ethanol boils = 78/101.3
At kPa pressure, Ethanol boils = 78/101.3 x 51 = 39.274°C

Why volume of gas decreases with pressure increases?

The volume of gas decreases with the increase of pressure because the pressure is volume both are inversely proportional to each other so when we increase pressure, the volume will decrease and when volume increases, pressure will be decreased.

Describe the density of the liquid?

The density of liquid depends upon its mass and volume. Liquids are denser than gases because molecules of liquids are closely packed and spaces between their molecules are negligible. The density of the liquid is expressed in the gram per cm3.

Why is the rate of diffusion in liquid slower than that of gas?

The rate of diffusion in liquid slower than that of gas because the liquid has stronger intermolecular forces as compared to gases so the rate of diffusion is slower than that of gases.

Why is liquid mobile?

The ease of flow of liquid is called mobility. Because the ease of flow of liquid depends upon the strength of intermolecular attractive forces. The weaker the strength of these forces, the more mobile is the liquid and vice versa. Due to this mobility of molecules, liquid can be proud from one vessel to another vessel.

Which is the lightest one, aluminum or gold?

Ans. Aluminum is higher than gold because the density of aluminum is lesser than gold. For example, the density of aluminum is 2.70gcm-3 and gold is 9.3gcm-3.

Which allotropic form of carbon is stable at room temperature (25°C)?

Diamond, graphic, and Buckyballs are stable forms of carbon at room temperature. Among these allotropic forms, graphite is energetically slightly more stable than diamond.

What is the relationship between the evaporation and the boiling point of a liquid?

A liquid having a higher boiling point will have slow evaporation due to stronger intermolecular forces. A liquid having a low boiling point will have faster evaporation.

Which parameters are kept constant in Charles’s Law?

In Charles’s law pressure remains constant.

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