Question

Which of the following statements is correct? (a) Heat is produced by the collision of gas molecules against one another. (b) When a gas is heated at constant volume, the molecules collide with one another more often.

Short answer

Only statement (b) is correct.

Step-by-step solution

Identify the Topic

The exercise involves the behavior of gas molecules, specifically under conditions of heat and volume, and it aligns with principles of the kinetic molecular theory.

Analyze Statement (a)

Statement (a) claims that heat is produced by the collision of gas molecules against one another. According to kinetic molecular theory, the temperature of a gas is related to the average kinetic energy of the molecules, not the collision itself. Thus, statement (a) is incorrect. Heat is a form of energy transfer, often resulting from temperature differences, but not directly produced by collisions.

Analyze Statement (b)

Statement (b) suggests that when a gas is heated at constant volume, molecules collide with one another more often. According to the kinetic molecular theory, when the temperature of a gas increases, the average kinetic energy of the gas molecules increases, leading to more frequent and energetic collisions. Hence, statement (b) is correct.

Key concepts

Gas Behavior

Understanding the behavior of gases is fundamental in the field of chemistry and physics. The kinetic molecular theory helps explain this behavior by providing a model where gas molecules are in constant, random motion. These molecules move in straight lines until they collide with either other molecules or the walls of their container.

• Gases expand to fill their containers because the molecules are constantly moving.
• The pressure exerted by a gas results from the collisions of its molecules with the container walls.

It is important to know that the individual collisions are not the source of heat. Instead, these collisions are crucial for defining other properties like pressure and temperature. Each molecule moves independently unless it's involved in a collision, meaning that gas molecules are usually far apart compared to the size of the molecules themselves.

Temperature Effects on Gases

Temperature is a vital factor that influences how gases behave. In the kinetic molecular theory, temperature is directly related to the average kinetic energy of the gas molecules. When the temperature of a gas increases, here's what happens:

• The molecules move faster owing to an increase in kinetic energy.
• This results in more frequent and more forceful collisions with the walls of the container.

When we refer to heating a gas at constant volume, we're saying the container's size doesn't change. So, as the gas's temperature rises, even if the space isn't expanding, the molecules still gain energy and collide more often. By experiencing more collisions, the pressure inside the container tends to increase if the volume is kept constant. This observation supports why statement (b) in the exercise is correct.

Energy Transfer in Gases

Energy transfer in gases involves the movement of heat, which is essentially energy in transit. According to the kinetic molecular theory, heat is not just produced by molecule collisions. Instead, heat is a form of energy transferred between substances or systems because of a temperature difference.

• When two systems at different temperatures come into contact, energy flows from the hotter to the cooler one until thermal equilibrium is reached.
• In the case of gases, this means faster-moving (hotter) molecules can transfer some of their kinetic energy to slower-moving (cooler) ones when they collide.

It's crucial to understand that energy transfer as heat concerns the overall kinetic energy of many molecules, not the individual collisions. Therefore, while collisions are a part of this process, they serve as mechanisms for energy distribution rather than its generation.