## New Simplified Chemistry Class 9 ICSE Solutions Study of Gas Laws

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**Viraf J Dalal Chemistry Class 9 Solutions and Answers**

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**Exercise**

**Question 1.(1988)**

“When stating the volume of a gas the pressure and temperature should also be given”. Why ?

**Answer:**

Volume of a gas under goes significant change if its pressure or temperature is slightly changed.

**Question 1.(1989)**

**Define or state :** Boyle’s Law

**Answer:**

**Boyle’s Law :** “Temperature remaining constant the volume of a given mass of dry gas is inversely proportional to its pressure.”

**Question 2.(1989)**

Express Kelvin Zero in °C

**Answer:**

Kelvin zero or absolute zero = — 273°C.

**Question 1.(1992)**

A fixed volume of a gas occupies 760cm^{3} at 27° C and 70cm of Hg. What will be its vol. at s.t.p. [637 cm^{3}]

**Answer:
**

**Question 1.(1993)**

**State :** Boyle’s Law

**Answer:**

**Boyle’s Law :** “Temperature remaining constant the volume of a given mass of dry gas is inversely proportional to its pressure.”

**Question 1.(1995)**

At 0°C and 760 mm Hg pressure, a gas occupies a volume of 10Q cm^{3}. The Kelvin temperature (Absolute temperature) of the gas is increased by one-fifth while the pressure is increased one and a half times. Calculate the final volume of the gas. [80 cc.]

**Answer:
**

**Question 1.(1996)**

The pressure on one mole of gas at s.t.p. is doubled and the temperature is raised to 546 K. What is the final volume of the gas ? [one mole of a gas occupies a volume of 22.4 litres at stp.] [22.4 ltrs.]

**Answer:
**

**Question 1.(1997)**

Is it possible to change the temperature and pressure of a fixed mass of gas without changing its volume. Explain your answer.

**Answer:**

No, it is not possible as change of any one of the parameters (pressure or temperature) has significant effect on volume.

**Additional Questions**

**Question 1.**

What volume will a gas occupy at 740 mm pressure which at 1480 nun occupies 500 cc ? [Temperature being constant] [1000 cc]

**Answer:
**

**Question 2.**

The volume of a given mass of a gas at 27°C is 100 cc. To what temperature should it be heated at the same pressure so that it will occupy a volume of 150 cc ?[177°C]

**Answer:
**

**Question 3.**

A fixed mass of a gas has a volume of 750 cc at—23°C and 800 mm pressure. Calculate the pressure for which its volume will be 720 cc. The temperature being —3°C. [900mm]

**Answer:
**

**Question 4.**

What temperature would be necessary to double the volume of a gas initially at s.t.p. if the pressure is decreased by 50% ? [0°C]

**Answer:
**

**Question 5.**

A gas cylinder having a capacity of 20 litres contains a gas at 100 atmos. How many flasks of 200 cm^{3} capacity can be filled from it at 1 atmos. pressure if the temperature remains constant ? [10,000]

**Answer:
**

**Question 6.**

A certain mass of gas occupied 850 ml at a pressure of 760 mm of Hg. On increasing the pressure it was found that the volume of the gas was 75% of its initial value. Assuming constant temperature, find the final pressure of the gas? [1013.33 mm of Hg]

**Answer:
**

**Question 7.**

It is required to reduce the volume of a gas by 20% by compressing it at a constant pressure. To do so, the gas has to be cooled. If the gas attains a final temperature of 157°C, find the initial temperature of the gas ? [264.5°C]

**Answer:
**

**Question 8.**

At a given temperature the pressure of a gas reduces to 75% of its initial value and the volume increases by 40% of its initial value. Find this temperature if the initial temperature was —10°C. [3.15°C]

**Answer:
**

**Study Of Gas Laws – Unit Test Paper 7**

**Q.1. Name or state the following :**

**Question 1.**

The law which states that pressure remaining constant the volume of a given mass of dry gas is directly proportional to its absolute [Kelvin] temperature.

**Answer:**

Charle’s Law.

**Question 2.**

The law which studies the relationship betweeir pressure of a gas and the volume occupied by it at constant temperature.

**Answer:**

Boyle’s Law.

**Question 3.**

An equation used in chemical calculations which gives a simultaneous effect of changes of temperature and pressure on the volume of a given mass of dry gas

**Answer:**

Gas equation.

**Question 4.**

The standard pressure of a gas in cm. of mercury corresponding to one atmospheric pressure.

**Answer:**

76 cm.

**Question 5.**

The absolute temperature value corresponding to 35°C.

**Answer:**

35 + 273 = 308K

**Q.2. Give reasons for the following :**

**Question 1.**

Gases unlike solids and liquids exert pressure in all directions.

**Answer:**

Impact of gas molecules with high velocity causes pressure to be exerted on the walls.

**Question 2.**

Gases have lower densities compared to solids or liquids.

**Answer:**

Gases have low densities as the inter-molecular distance between the molecules of gases is very large.

**Question 3.**

Temperature remaining constant the product of the vol. & the press, of a given mass of dry gas is a constant.

**Answer:
**

**Question 4.**

All temperatures on the Kelvin scale are in positive figures.

**Answer:**

All temperatures on the Kelvin scale are in positive figures.

The temperature -273°C = OK [Absolute zero or zero Kelvin]

Hence it may be negative or positive on Celsius scale, it is always positive on Kelvin as 0°C = 0 + 273 = 273K

30°C = 30 + 273 = 303 K

– 70°C = – 70+ 273;= 203 K

– 273°C = – 273 + 273 = 0K

**Question 5.**

Volumes of gases are converted into s.t.p. conditions and then compared.

**Answer:**

Volumes of gases are converted into s.t.p. conditions and then compared as

**volumes of gases change with temperature and pressure –** hence a standard value of temperature and pressure is chosen to which gas volumes are referred.

**Q.3. Calculate the following :**

**Question 1.**

Calculate the temperature to which a gas must be heated, so that the volume triples without any change in pressure. The gas is originally at 57”C and having a volume 150 cc.

**Answer:
**

**Question 2.**

A gas ‘X’ at -33°C is heated to 127° C at constant pressure. Calculate the percentage increase in the volume of the gas.

**Answer:
**

**Question 3.**

Calculate the volume of a gas ‘A’ at s.t.p., if at 37°C and 775 mm of mercury pressure, it occupies a volume of 9 1/2 litres.

**Answer:
**

**Question 4.**

Calculate the temperature at which a gas ‘A’ at 20°C having a volume, of 500 cc. will occupy a volume of 250 cc.

**Answer:
**

**Question 5.**

A gas ‘X’ is collected over water at 17°C and 750 mm. pressure. If the volume of the gas collected is 50 cc., calculate the volume of the dry gas at s.t.p. [at 17°C the vapour pressure is 14 mm.]

**Answer:
**

**Q.4. Assuming temperature remaining constant calculate the pressure of the gas in each of the following :**

**Question 1.**

The pressure of a gas having volume 1000 cc. originally occupying 1500 cc. at 720 mm. pressure.

**Answer:
**

**Question 2.**

The pressure of a gas having volume 100 lits. originally occupying 75 dm^{3} at 700 mm. pressure.

**Answer:
**

**Question 3.**

The pressure of a gas having volume 380 lits. originally occupying 800 cm^{3} at 76 cm. pressure.

**Answer:
**

**Question 4.**

The pressure of a gas having volume 1800 ml. originally occupying 300 ml. at 6 atms. pressure.

**Answer:
**

**Question 5.**

The pressure of a gas having volume 1500 cm^{3} originally occupying 750 cc. at 5 ats. pressure.

**Answer:
**

**Q.5. Calculate the following :**

**Question 1.**

The temp, at which 500 cc. of a gas ‘X’ at temp. 293K occupies half it’s original volume [pressure constant].

**Answer:
**

**Question 2.**

The volume at s.t.p. occupied by a gas “Y” originally occupying 760 cc. at 300K and 70 cm. press, of Hg.

**Answer:
**

**Question 3.**

The volume at s.t.p. occupied by a gas ‘Z’ originally occupying 1.57 dm^{3} at 310.5K and 75 cm. press. of Hg.

**Answer:
**

**Question 4.**

The volume at s.t.p. occupied by a gas ‘Q’ originally occupying 153.7 cm^{3} at 287K and 750 mm. pressure [vapour pressure of gas ‘Q’ at 287K is 12 mm of Hg.]

**Answer:
**

**Question 5.**

The temperature to which a gas ‘P’ has to be heated to triple it’s volume, if the gas originally occupied 150 cm^{3} at 330K [pressure remaining constant].

**Answer:
**

**Q.6. Fill in the blanks with the correct word, from the words in bracket :**

**Question 1.**

If the temperature of a fixed mass of a gas is kept constant and the pressure is increased, the volume correspondingly ____ [increases / decreases]

**Answer:**

If the temperature of a fixed mass of a gas is kept constant and the pressure is increased, the volume correspondingly **decreases.**

**Question 2.**

If the pressure of a fixed mass of a gas is kept constant and the temperature is increased, the volume correspondingly ____ [increases / decreases]

**Answer:**

If the pressure of a fixed mass of a gas is kept constant and the temperature is increased, the volume correspondingly **increases.**

**Question 3.**

1 dm3 of a gas is equal to ____ [1 litre / 100ml. / 100 cc.]

**Answer:**

1 dm3 of a gas is equal to **1 litre.**

**Question 4.**

All the temperature on the kelvin scale are in ____ figures [negative positive]

**Answer:**

All the temperature on the kelvin scale are in **positive** figures.

**Question 5.**

At -273°C the volume of a gas is theoretically ____ [272 cc. / 0 cc. / 274 cc.]

**Answer:**

At -273°C the volume of a gas is theoretically **0 cc. **

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