According to the kinetic molecular theory, which of the following gases has molecules with the greatest average kinetic energy at 25°C?

• A. Oxygen (O2)
• B. All gases have the same average kinetic energy at the same temperature.
• C. Carbon dioxide (CO2)
• D. Hydrogen (H2)

Answer: (B)

Verified step by step guidance

1. Recall the kinetic molecular theory states that the average kinetic energy of gas molecules depends only on the temperature, not on the type or mass of the gas.
2. Write the formula for the average kinetic energy of a gas molecule: \(\text{KE}_{avg} = \frac{3}{2} k_B T\), where \(k_B\) is Boltzmann's constant and \(T\) is the absolute temperature in kelvins.
3. Note that since \(k_B\) is a constant and the temperature \(T\) is the same for all gases at 25°C, the average kinetic energy will be the same for all gases regardless of their molecular mass or identity.
4. Understand that while the average kinetic energy is the same, the speeds of the molecules differ because lighter molecules move faster to have the same kinetic energy as heavier molecules.
5. Conclude that at 25°C, oxygen (O2), carbon dioxide (CO2), and hydrogen (H2) all have the same average kinetic energy according to the kinetic molecular theory.