According to the kinetic molecular theory, why do the molecules of a substance move quickly at higher temperatures?

• A. Because the molecules are larger in size.
• B. Because the substance has a higher density.
• C. Because intermolecular forces become stronger.
• D. Because they have greater average kinetic energy.

Answer: (D)

Verified step by step guidance

1. Recall the kinetic molecular theory, which states that the temperature of a substance is directly related to the average kinetic energy of its molecules.
2. Understand that kinetic energy of a molecule is given by the formula \(KE = \frac{1}{2} m v^2\), where \(m\) is the mass and \(v\) is the velocity of the molecule.
3. Recognize that as temperature increases, the average kinetic energy of the molecules increases, which means the molecules move faster on average.
4. Note that molecular size, density, and intermolecular forces do not directly cause the increase in molecular speed with temperature; rather, it is the increase in kinetic energy due to temperature.
5. Conclude that the correct reason molecules move quickly at higher temperatures is because they have greater average kinetic energy.