Which of the following describes what happens as the temperature of a gas in a balloon increases, according to the kinetic molecular theory?

• A. The gas molecules decrease in size.
• B. The gas molecules move more slowly.
• C. The number of gas molecules in the balloon increases.
• D. The average kinetic energy of the gas molecules increases.

Answer: (D)

Verified step by step guidance

1. Recall the kinetic molecular theory, which explains the behavior of gas particles in terms of their motion and energy.
2. Understand that the size of gas molecules is considered constant and does not change with temperature, so the statement about molecules decreasing in size is incorrect.
3. Recognize that as temperature increases, the average speed of gas molecules increases, so they do not move more slowly; this eliminates that option.
4. Note that the number of gas molecules in a closed balloon remains constant unless gas is added or removed, so the number does not increase with temperature.
5. Conclude that increasing temperature leads to an increase in the average kinetic energy of gas molecules, which is directly proportional to temperature according to the equation \(\text{KE}_{\text{avg}} = \frac{3}{2}RT\), where \(R\) is the gas constant and \(T\) is the temperature in Kelvin.