I keep getting “Temperature and molecular kinetic energy” questions wrong in Kinetic Theory of Gases. What's the trap?
saying every molecule has the same speed at a given temperature.
The usual trap: saying every molecule has the same speed at a given temperature. How to avoid it: same average energy, lighter molecules move faster. Go back to the definition — For an ideal gas, absolute temperature measures average translational kinetic energy per molecule: 3k_BT/2. At the same temperature, light and heavy molecules have the same average translational energy but different rms speeds.
Key point
Temperature and molecular kinetic energy
Common mistake
saying every molecule has the same speed at a given temperature.
Memory tip
same average energy, lighter molecules move faster.
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