Problem 1 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following statements is wrong for gases? (a) gases do not have a definite shape and volume (b) volume of the gas is equal to volume of container the confining the gas (c) confirmed gas exerts uniform pressure on the walls of its container in all directions (d) mass of gas cannot be determined by weighing a container in which it is enclosed

Step-by-Step Solution

Answer

Statement (d) is wrong.

Step 1: Understand the Properties of Gases

Gases are known for having indefinite shape and volume, meaning they take both the shape and volume of their container. This is because gas particles move freely and expand to fill the entire space available.

Step 2: Analyze Statement (a)

Statement (a) claims that gases do not have a definite shape and volume. This is true as gases conform to the shape and volume of their container.

Step 3: Analyze Statement (b)

Statement (b) claims that the volume of the gas is equal to the volume of the container confining the gas. This is also true since gases expand to fill the container they are in.

Step 4: Analyze Statement (c)

Statement (c) asserts that gas exerts uniform pressure on the walls of its container in all directions. This statement is true as well, according to the kinetic molecular theory of gases.

Step 5: Analyze Statement (d)

Statement (d) suggests that the mass of gas cannot be determined by weighing the container in which it is enclosed. This statement is false because the mass of a gas can indeed be determined by weighing the container with and without the gas and calculating the difference.

Key Concepts

Indefinite Shape and Volume

Gases are unique among the states of matter in that they do not have a fixed shape or volume. This is often because the molecules in a gas are not bound in a rigid structure or closely packed, as is the case with solids and liquids. Instead, gas molecules move freely and rapidly, leading them to fill the entirety of any container they occupy. For example, if you release a gas into a balloon, it will spread and fill every part of the balloon, making the balloon swell. Once the gas fills the container, its volume becomes equal to that of its container, and it takes on its shape. This behavior highlights the intrinsic property that gases have of adapting to their surroundings by assuming an indefinite shape and volume.

Kinetic Molecular Theory

The kinetic molecular theory is a fundamental concept that helps us understand the behavior of gases. According to this theory, gas particles are in constant, random motion, moving in straight paths until they collide with each other or the walls of their container. These collisions are elastic, meaning they do not lose energy but rather transfer it or redirect their movement.

• Gas particles are so small compared to the distances between them that any attractive or repulsive forces between them are negligible.
• The average kinetic energy of gas particles is directly proportional to the temperature of the gas, meaning higher temperatures increase movement.
• Pressure exerted by gas is due to the collisions of particles with the walls of their container, creating a uniform pressure in all directions.

This theory not only explains why gases fill their containers but also underlies the principles behind gas laws, such as Boyle's Law and Charles's Law.

Gas Pressure Measurement

Measuring the pressure of a gas involves understanding the force that the gas particles exert on the container walls. Pressure is defined as force per unit area, which in the context of gases translates to the frequency and force of particle collisions. Various tools and units can be used to measure gas pressure, such as:

• Barometer: Commonly used for measuring atmospheric pressure, indicating how much the air weighs.
• Manometer: Used to measure the pressure of gases in a closed container, comparing it to atmospheric pressure.
• Units: Common units for pressure include atmospheres (atm), pascals (Pa), and millimeters of mercury (mmHg).

When measuring gas pressure, it’s crucial to ensure that the container is completely sealed. Otherwise, leaks can lead to inaccurate readings by allowing gas to escape and thus reducing the pressure inside the container.

Mass of Gases

Determining the mass of a gas can seem perplexing due to its lack of definite shape and volume. However, it is quite straightforward through indirect means. By weighing a container both filled with the gas and empty, you can calculate the gas's mass by finding the difference between the two measurements.

• First, weigh the container without the gas to get a baseline mass.
• Next, fill the container with gas and weigh it again.
• The difference between these two weights gives you the mass of the gas.

This method is particularly useful because gases can be challenging to handle directly due to their invisible nature and tendency to escape. It's important to ensure that the container is well-sealed to prevent any gas from leaking out during the weighing process.