**Class 11 Chemistry States of Matter Gases !!!**

**Important multiple choose questions:**

**At absolute zero , molecules of hydrogen gas has 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 gaseous state. **

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

**An ideal gas can never be liquefied b/c:**

1.**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 liquid state.**

**Gases are less dense and highly compressible due to:**

1.**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 dm**^{3}**= 0.0224 m3**

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

** R= ****0.0224 m**^{3}** x 101325 ****N****m**^{-2 }** **

** **** 1mol x 273 K**

** R = 8.314 Nm ^{2} 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 mass of an ideal gas, its volume can be kept constant by:**

1.**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 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 ideal gas at STP has the same volume of 22.4 dm ^{3}**

2.**Celsius and Fahrenheit temperature coincides at -40 ^{0}**

3.**S.I unit for 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:** 1.**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 occur due to :**

1.**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 occur due to large empty spaces among the molecules which are in constant random motion.**

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

1.**Higher average kinetic energy**

2.**Higher rates of diffusion**

3.**Lower rates of diffusion**

4.**Higher vapor pressures**

**Answer ) Lower rates of diffusion**

**Brief Explanation :**

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

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

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