Class 11 Chemistry States of Matter Gases

Important multiple choice questions:

At absolute zero, molecules of hydrogen gas have energy:

1. Translational only

2. Rotational only

3. Vibrational only

4. None of these

Answer ) None of these

Brief Explanation :

Absolute zero is the lowest possible temperature at which no gas can exist in a gaseous state.

All types of molecular motions stop at this temperature and molecules have no kinetic energy.

An ideal gas can never be liquefied b/c:

Molecules are smaller

2. Molecules are non-polar

3. Molecules are non-interacting

4. Solidifies directly

Answer ) Molecules are non-interacting

Brief Explanation :

An ideal gas can never be liquefied because its molecules are non-interacting i.e. have no attractive forces to change them into a liquid state.

Gases are less dense and highly compressible due to:

Small size of molecules

2.No attraction among molecules

3. High kinetic energy of molecules

4. Larger empty spaces among molecules

Answer ) Larger empty spaces among molecules

Brief Explanation :

Gases are separated by large empty spaces & thus gases are less dense and highly compressible.

A hyperbolic plot of P versus V for a gas at constant temperature means that :

Answer ) Both 2 & 3

Avogadro’s law states that for different gases:

Combined gas law states that:

The value of Universal gas constant R in S.I unit is:

1.1.987 cal.k^-1.mol^-1

2.8.314 J.k^-1.mol^-1

3.0.0821 L.atm.k^-1.mol^-1

4.All of these

Answer ) 8.314 J.K^-1 mol^-1

Brief Explanation :

The value of universal gas constant in S.I units is , which can be calculated by taking:

n=1mol : P = 1atm = 101325 Nm^-2

V= 22.4 dm³= 0.0224 m3

Now we have that R= P x V / n x T

R= 0.0224 m³ x 101325 Nm^-2 /1mol x 273 K

R = 8.314 Nm² K^-1 . mol^-1

or R = 8.314 J K^-1 . mol^-1

When gas is compressed , its mass:

1.Increase

2.Decreases

3.Disappears

4.Remains Constant

Answer ) Remains Constant

Brief Explanation :

When a gas is compressed , the molecules come closer & inter- molecular spaces decreases but the mass remains the same.

At the same temperature and pressure, different gases have the same:

1.Average molecular speeds

2.Average Kinetic energy

3.Molecular masses

4.Density

Answer ) Average Kinetic energy

By increasing the mass of an ideal gas, its volume can be kept constant by:

Lowering T & P

2. Raising T & P

3. Raising P & Lowering T

4. Lowering T & applying P

Answer ) Raising P & Lowering T

Brief Explanation :

When the mass of an ideal gas is increased, its volume can be kept constant by applying pressure & decreasing temperature.

It will bring the gas molecules closer together to keep the volume constant when mass is increased.

Pick up the correct statement:

1.1 mole of an ideal gas at STP has the same volume of 22.4 dm³

2. Celsius and Fahrenheit’s temperature coincides at -40⁰

3.S.I unit for the pressure of a gas is Pascal

4. All of these

Answer ) All of these

Brief Explanation :

All the given statements are correct.

A process that clearly suggests that matter is made up of tiny particles, which are in constant random motion, is:

Condensation

2. Combustion

3. Conduction

4. Diffusion

Answer ) Diffusion

Brief Explanation :

Diffusion provides evidence that matter consists of tiny particles which are in constant random motion b/c diffusion can occur when the particles are separated by empty spaces.

Diffusion of gases occurs due to :

Empty spaces among molecules

2. Collisions among molecules

3. Attraction among molecules

4. None of these

Answer ) Empty spaces among molecules

Brief Explanation :

Diffusion of gases occurs due to large empty spaces among the molecules which are in constant random motion.

As compared to the lighter gases, heavier gas molecules have :

Higher average kinetic energy

2. Higher rates of diffusion

3. Lower rates of diffusion

4. Higher vapour pressures

Answer ) Lower rates of diffusion

Brief Explanation :

At the same temperature & pressure, heavier gas molecules have Lower velocity than lighter gas molecules.

As the rate of diffusion is directly proportional to velocity, hence heavier gas molecules have a lower rate of diffusion than the lighter gas molecules at the same temperature and pressure.