Asked in UHS MDCAT 2012 2012Moderate

H2 and O2 both are at thermal equilibrium at temperature 300 K. Oxygen molecule is 16 times massive than hydrogen. Root mean square speed of hydrogen is:

Correct answer: A. 4 root mean square of oxygen

  • A. 4 root mean square of oxygen
  • B. ¼ root mean square of oxygen
  • C. 1/16 root mean square of oxygen
  • D. 1/6 root mean square of oxygen

Explanation

At the same temperature v_rms is inversely proportional to the square root of molecular mass, since v_rms = sqrt(3kT/m). Oxygen is 16 times heavier, so v_H/v_O = sqrt(16) = 4. Hydrogen molecules move four times faster than oxygen molecules at 300 K.

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Thermal equilibrium and heat explain how temperature and energy transfer are related, while molar specific heats describe the heat required by a gas at constant volume or constant pressure. The first law connects heat supplied, work done and change in internal energy, with sign conventions kept distinct from temperature changes.

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