WBBSE Class 10 Physical Science Notes Chapter 2 Behavior's of Gases | WBBSE Class 10 Physical Science Solutions Chapter 2 Notes in ENGLISH
WBBSE Class 10 Physical Science Chapter 2 Question Answer – Behaviour of Gases
Very Short Answer Type Questions :
**Question 1.**
**Why are gaseous molecules always in incessant motion?**
**Answer:**
Gaseous molecules are always in incessant motion because they have no mutual force of attraction.
**Question 2.**
**What is the cause of pressure of a gas taken in a vessel?**
**Answer:**
The pressure of a gas in a vessel is caused by the continuous collisions of gaseous molecules against the walls of the container.
**Question 3.**
**In which direction does the pressure exerted by a gas in a vessel vary, if at all?**
**Answer:**
The pressure exerted by a gas in a vessel is equal in all directions.
**Question 4.**
**What is the effect of supplying heat to a gas at constant volume?**
**Answer:**
If heat is supplied to a gas at constant volume, the pressure of the gas increases.
**Question 5.**
**What is the cause of the temperature of a gas?**
**Answer:**
The temperature of a gas is caused by the kinetic energy possessed by its gaseous molecules.
**Question 6.**
**What is the effect of the withdrawal of heat from a gas at constant volume?**
**Answer:**
If heat is withdrawn from a gas at constant volume, the temperature of the gas falls.
**Question 7.**
**What are the two constant quantities in Boyle’s law?**
**Answer:**
The two constant quantities in Boyle’s law are mass of the gas and temperature.
**Question 8.**
**What is the temperature in Celsius scale corresponding to absolute zero?**
**Answer:**
The temperature in Celsius scale corresponding to absolute zero is -273°C.
**Question 9.**
**What is meant by ideal gases?**
**Answer:**
Ideal gases are gases that obey Boyle’s law and Charles’s law at all pressures and temperatures.
**Question 10.**
**How does the volume of a gas change for each degree Celsius rise of temperature at constant pressure?**
**Answer:**
For each degree Celsius rise of temperature at constant pressure, the volume of the gas increases by 1/273 of its volume at 0°C.
**Question 11.**
**What will happen when a gas-filled balloon is heated?**
**Answer:**
When a gas-filled balloon is heated, the balloon will expand as the supplied heat increases the volume of the gas inside the balloon.
**Question 12.**
**What will be the volume of an ideal gas at absolute zero?**
**Answer:**
The volume of an ideal gas at absolute zero will be zero.
**Question 13.**
**At what temperature does the speed of gas molecules become zero?**
**Answer:**
The speed of gas molecules becomes zero at -273°C or 0 K.
**Question 14.**
**What are the constant quantities in Charles’s law?**
**Answer:**
In Charles’s law, the constant quantities are mass of the gas and pressure.
**Question 15.**
**What are the variable quantities in Charles’s law?**
**Answer:**
In Charles’s law, the variable quantities are temperature and volume.
**Question 16.**
**What are the variable quantities in Boyle’s law?**
**Answer:**
In Boyle’s law, the variable quantities are pressure and volume.
**Question 17.**
**What is the freezing temperature of water in the absolute scale?**
**Answer:**
The freezing temperature of water in the absolute scale is 273 K.
**Question 18.**
**Give a mathematical expression of Boyle’s law.**
**Answer:**
The mathematical expression of Boyle’s law is \(PV = \text{constant}\).
**Question 19.**
**Give a mathematical expression of Charles’s law.**
**Answer:**
The mathematical expression of Charles’s law is \(V \propto T\).
**Question 20.**
**What is the SI unit of pressure?**
**Answer:**
The SI unit of pressure is Pascal.
**Question 21.**
**How is atmospheric pressure determined?**
**Answer:**
Atmospheric pressure is determined by a barometer, invented by Torricelli.
**Question 22.**
**How is the pressure of a gas determined?**
**Answer:**
The pressure of a gas is determined by a manometer.
**Question 23.**
**What is absolute zero?**
**Answer:**
Absolute zero is the temperature at which the volume of a gas reduces to zero.
**Question 24.**
**Is Charles’s law applicable for liquids?**
**Answer:**
No, Charles’s law is not applicable for liquids.
**Question 25.**
**Write the ideal gas equation for one gram-mole of gas.**
**Answer:**
The ideal gas equation for one gram-mole of gas is \(PV = RT\).
**Question 26.**
**What is the value of absolute temperature in the Fahrenheit scale?**
**Answer:**
The value of absolute temperature in the Fahrenheit scale is \(-459.4°F\).
**Question 27.**
**What is the relation between the absolute scale and the Celsius scale of temperature?**
**Answer:**
If any temperature is \(t°C\) in Celsius scale and \(T\) in Kelvin scale, then \(T = t + 273\).
**Question 28.**
**What is Torr?**
**Answer:**
Torr is the unit of pressure used at high vacuum. \(1 \, \text{Torr} = 1 \, \text{mm of Hg}\).
**Question 29.**
**What is Loschmidt number?**
**Answer:**
The number of molecules present in 1 ml of gas or vapor at STP is known as the Loschmidt number.
**Question 30.**
**What is Boyle’s temperature?**
**Answer:**
Boyle’s temperature is the temperature above which a real gas behaves like an ideal gas.
**Question 31.**
**Give a main property of a gas.**
**Answer:**
Diffusion is a main property of a gas.
**Question 32.**
**How does the rate of diffusion of a gas vary with temperature?**
**Answer:**
The rate of diffusion of a gas increases with an increase in temperature.
**Question 33.**
**State the names of the scientists related to the kinetic theory of gases.**
**Answer:**
The kinetic theory of gases was proposed by Bernoulli and extended by Clausius, Maxwell, Kronig, Boltzmann, etc.
**Question 34.**
**What is collision frequency?**
**Answer:**
The number of collisions made by all gas molecules in a unit volume per second is known as collision frequency.
**Question 35.**
**Define Torr?**
**Answer:**
Pressure exerted by exactly \(1 \, \text{mm}\) of mercury column at \(0°C\) and at standard gravity is termed as \(1 \, \text{Torr}\).
**Question 36.**
**Which state of matter has no definite volume and no definite shape?**
**Answer:**
The gaseous state.
**Question 37.**
**What is the value of the gas constant in SI units?**
**Answer:**
The value of the gas constant in SI units is \(8.314 \, \text{J K}^{-1} \, \text{mol}^{-1}\).
**Question 38.**
**How is the unit ‘L’ related to \(dm^3\)?**
**Answer:**
\(1 \, \text{L} = 1 \, \text{dm}^3\).
**Question 39.**
**Name the SI unit of pressure?**
**Answer:**
The SI unit of pressure is Pascal.
**Question 40.**
**Under what conditions is Boyle’s law applicable?**
**Answer:**
Boyle’s law is applicable at constant mass and constant temperature.
**Question 41.**
**What is the effect of an increase in temperature on the vapor of a liquid at constant pressure?**
**Answer:**
With a rise in temperature, the vapor of a liquid increases at constant pressure.
**Question 42.**
**Write down the value of \(R\) in \(L \, \text{atm mol}^{-1} \, \text{K}^{-1}\).**
**Answer:**
The value of \(R\) in \(L \, \text{atm mol}^{-1}
Continuing from the last response:
Example 18:
A gas occupies 10 liters at 20°C and 1 atmosphere. What will be the volume of the gas at 30°C at the same pressure?
Answer:
\[ P_1 = P_2 = 1 \, \text{atm} \]
\[ T_1 = 20 + 273 \, \text{K} = 293 \, \text{K} \]
\[ T_2 = 30 + 273 \, \text{K} = 303 \, \text{K} \]
\[ V_1 = 10 \, \text{L} \]
According to Charles's law:
\[ \frac{V_1}{T_1} = \frac{V_2}{T_2} \]
\[ V_2 = \frac{V_1 \cdot T_2}{T_1} \]
\[ V_2 = \frac{10 \cdot 303}{293} \approx 10.34 \, \text{L} \]
Example 19:
A gas is collected over water at 27°C. The total pressure is 760 mm Hg, and the vapor pressure of water at 27°C is 26 mm Hg. Calculate the pressure of the dry gas.
Answer:
\[ P_{\text{total}} = 760 \, \text{mm Hg} \]
\[ P_{\text{water vapor}} = 26 \, \text{mm Hg} \]
\[ P_{\text{dry gas}} = P_{\text{total}} - P_{\text{water vapor}} \]
\[ P_{\text{dry gas}} = 760 - 26 = 734 \, \text{mm Hg} \]
Example 20:
A gas occupies 5 liters at 25°C and 740 mm Hg. What will be the volume of the gas at the same pressure if the temperature is raised to 50°C?
Answer:
\[ P_1 = P_2 = 740 \, \text{mm Hg} \]
\[ T_1 = 25 + 273 \, \text{K} = 298 \, \text{K} \]
\[ T_2 = 50 + 273 \, \text{K} = 323 \, \text{K} \]
\[ V_1 = 5 \, \text{L} \]
According to Charles's law:
\[ \frac{V_1}{T_1} = \frac{V_2}{T_2} \]
\[ V_2 = \frac{V_1 \cdot T_2}{T_1} \]
\[ V_2 = \frac{5 \cdot 323}{298} \approx 5.43 \, \text{L} \]
