According to the kinetic molecular theory, how does the average speed of water molecules change as the temperature of the water increases?

• A. The average speed of the molecules increases.
• B. The average speed of the molecules decreases.
• C. The average speed of the molecules fluctuates randomly.
• D. The average speed of the molecules remains constant.

Answer: (A)

Verified step by step guidance

1. Recall that the kinetic molecular theory relates the temperature of a substance to the average kinetic energy of its molecules.
2. Understand that the average kinetic energy (KE) of molecules is directly proportional to the absolute temperature (in Kelvin), expressed as \(KE_{avg} = \frac{3}{2} k_B T\), where \(k_B\) is the Boltzmann constant and \(T\) is the temperature.
3. Recognize that the kinetic energy of a molecule is also related to its mass (\(m\)) and average speed (\(v_{avg}\)) by the equation \(KE_{avg} = \frac{1}{2} m v_{avg}^2\).
4. Combine these relationships to see that as temperature \(T\) increases, the average kinetic energy increases, which means the average speed \(v_{avg}\) of the molecules must increase to satisfy \(\frac{1}{2} m v_{avg}^2 \propto T\).
5. Conclude that increasing the temperature of water increases the average speed of its molecules according to the kinetic molecular theory.