Chemistry Class 11 NCERT Solutions: Chapter 5 States of Matter Part 6

Q: 18. 2.9 g of a gas at 95 ° C occupied the same volume as 0.184 g of dihydrogen at 17 °C, at the same pressure. What is the molar mass of the gas?

Answer:

Volume (V) occupied by dihydrogen is given by,

Equation

Equation

Let M be the molar of the unknown gas. Volume (V) occupied by the unknown gas can be calculated as: Equation

Equation

According to the question,

Equation

Equation

Equation

Equation

Hence, the molar mass of the gas is Equation .

Q: 19. A mixtures of dihydrogen and Dioxygen at one bar pressure contain Equation by weight of dihydrogen. Calculate the partial pressure of dihydrogen.

Answer:

Let the weight of dihydrogen be 20 g and the weight of Dioxygen be 80 g.

Then, the number of moles of dihydrogen, Equation and the number of moles

Of Dioxygen, Equation

Given,

Total pressure of the mixture, Equation

Then, partial pressure of dihydrogen,

Equation

Equation

Equation

Hence, the partial pressure of dihydrogen is Equation

Q: 20. What would be the SI unit for the quantity Equation

Answer:

The SI unit for pressure, p is Equation

Equation

The Equation

The SI unit for the number of moles Equation is mol.

Therefore, the SI unit for quantity Equation is given by,

Equation

Equation

Q: 21. In terms of Charles’ law explain why Equation is the lowest possible temperature.

Answer:

Charles’ law states that constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute temperature.

It was found that for all gases (at any given pressure), the plots of volume vs. temperature (in Equation is a straight line. If this line is extended to zero volume, then it intersects the temperature-axis at Equation . In other words, the volume of any gas at Equation is zero. This is because all gases get liquefied before reaching a temperature of Equation . Hence, it can be concluded that Equation is the lowest possible temperature.

Q: 22. Critical temperature for carbon dioxide and methane are Equation and Equation respectively. Which of these has stronger intermolecular forces and why?

Answer:

Higher is the critical temperature of a gas, easier is its liquefaction. This means that the intermolecular forces of attraction between the molecules of a gas are directly proportional to its critical temperature; Hence, intermolecular forces of attraction are stronger in the case of Equation .

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