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The average kinetic energy of a molecule of an ideal gas is directly proportional to its

  1. A.Pressure
  2. B.Volume
  3. C.Absolute temperature
  4. D.Molar mass

Correct answer

C. Absolute temperature

Explanation

The correct answer is C, absolute temperature. The kinetic theory gives the average kinetic energy of a molecule as three halves of the product of the Boltzmann constant and the absolute temperature, and for one mole as three halves of RT. Temperature is therefore a direct measure of the average kinetic energy of random molecular motion, and at the same temperature a hydrogen molecule and an oxygen molecule have the same average kinetic energy even though the hydrogen molecule moves much faster. A, pressure depends on how often and how hard molecules strike the walls, which involves the number density as well, so it is not the measure of molecular energy. B, volume does not appear in the expression at all. D, molar mass affects the speed of the molecules, not their average kinetic energy; a heavier molecule simply moves more slowly to carry the same energy.

Read the full article: Gas Laws and Kinetic Theory of Gases: Formulas and PYQs

Practice Questions

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Q1.General ScienceEasy

Boyle's law states that at constant temperature, the volume of a fixed mass of gas is

  1. A.Directly proportional to its pressure
  2. B.Inversely proportional to its pressure
  3. C.Independent of its pressure
  4. D.Proportional to the square of its pressure
Show answer
Correct answer: B. Inversely proportional to its pressure

Boyle's law, established in 1662, says that for a fixed mass of gas at constant temperature the product of pressure and volume stays constant, so doubling the pressure halves the volume.

Q2.General ScienceEasy

A hot air balloon rises because warm air

  1. A.Becomes denser than the surrounding air
  2. B.Expands and becomes less dense than the surrounding air
  3. C.Loses its mass on heating
  4. D.Has a lower specific heat than cold air
Show answer
Correct answer: B. Expands and becomes less dense than the surrounding air

By Charles's law the volume of a fixed mass of gas at constant pressure is proportional to its absolute temperature, so heating the air inside the envelope makes it expand; some of it escapes from the open mouth, the mass of air left inside falls, its density becomes lower than…

Q3.General ScienceEasy

Absolute zero of temperature is equal to

  1. A.0 degrees Celsius
  2. B.-100 degrees Celsius
  3. C.-273.15 degrees Celsius
  4. D.-373.15 degrees Celsius
Show answer
Correct answer: C. -273.15 degrees Celsius

Extending the straight line of Charles's law backwards shows that the volume of an ideal gas would become zero at minus 273.15 degrees Celsius, and this point is taken as the zero of the kelvin or absolute scale, at which molecular motion carries its least possible energy.

Q5.General ScienceMedium

The volume occupied by one mole of an ideal gas at 273.15 K and one atmosphere pressure is about

  1. A.11.2 litres
  2. B.22.4 litres
  3. C.44.8 litres
  4. D.1 litre
Show answer
Correct answer: B. 22.4 litres

Substituting one mole, 273.15 kelvin and one atmosphere in the ideal gas equation gives a volume of 22.4 litres, the molar volume at standard temperature and pressure, and this is the figure used in mole calculations; with the modern standard pressure of one bar the value works out to about…