According to the kinetic molecular theory, which of the following samples contains particles that are vibrating fastest?

• A. Steam at 120 °C
• B. Liquid water at 0 °C
• C. Liquid water at 25 °C
• D. Ice at -10 °C

Answer: (A)

Verified step by step guidance

1. Recall that according to the kinetic molecular theory, the average kinetic energy of particles is directly proportional to the absolute temperature (in Kelvin). This means particles move faster at higher temperatures.
2. Convert all given temperatures from Celsius to Kelvin using the formula: \(T(K) = T(^\circ C) + 273.15\).
3. Compare the Kelvin temperatures of each sample: steam at 120 °C, liquid water at 0 °C, liquid water at 25 °C, and ice at -10 °C.
4. Understand that particles in the gas phase (steam) generally have higher kinetic energy and move faster than those in liquid or solid phases at the same temperature, because gases have more freedom of movement.
5. Conclude that since steam at 120 °C has the highest temperature and is in the gas phase, its particles are vibrating (moving) fastest compared to the other samples.