Kinetic theory and gas laws – MCQs (set 2)

Which one of the following does not express Boyle’s Law?

The pressure exerted by an ideal gas, maintained at a constant temperature, is inversely proportional to the volume occupied by the gas. Which of the following statements is not true?

• The average molecular kinetic energy remains constant.

• The gas must consist of identical molecules.

• The mass of gas is fixed.

• The number of molecules in the gas doesn’t change.

A mixture of helium He and hydrogen H₂ gases is maintained at a temperature of 300 K. Which of the following is correct?

• The average kinetic energy of the He molecules is greater than the average kinetic energy of the H₂ molecules.

• The average kinetic energy of the He molecules is the same as the average kinetic energy of the H₂ molecules.

• The average speed of the He molecules is greater than the average speed of the H₂ molecules.

• The average speed of the He molecules is the same as the average speed of the H₂ molecules.

The average kinetic energy of the molecules in an ideal gas is proportional to

• the number of molecules in the gas.

• the specific heat capacity of the gas.

• the temperature of the gas.

• the total mass of the gas.

Two different sized boxes, P and Q, both contain the same number of nitrogen molecules. The molecules in box P have twice the r.m.s. speed of those in box Q. Which of the following must be correct?

• The density of the gas in box P is greater than in box Q.

• The mean momentum of the molecules in box P is greater than those in box Q.

• The pressure exerted by the gas in box P is greater than that in box Q.

• The temperature of the gas in box P is greater than that in box Q.

Separate samples of methane and nitrogen gas have the same volume and each gas is at the same temperature and pressure.

• Each gas has the same mass.

• Both gases have the same number of molecules.

• Molecules of each gas have the same number of atoms.

• The densities of both gases are the same.

The absolute temperature scale is a theoretical scale proposed by Lord Kelvin. On this scale, zero is the temperature at which

• all gases become liquids.

• an ideal gas would exert no pressure.

• the Celsius temperature is −373°C.

• water freezes.

The Moon has no atmosphere because

• it is far away from the surface of the Earth.

• its surface temperature is 10°C.

• the r.m.s. velocity of the gas molecules is more than the escape velocity at the Moon’s surface.

• the escape velocity of the Moon’s surface is more than the r.m.s velocity of the molecules.

The r.m.s. speed of an ideal gas at 300 K is 1.8 km/s. What is the r.m.s. speed of the same gas at 1200 K?

• 13 km/s

• 7.2 km/s

• 3.6 km/s

• 2.5 km/s

• 1.9 km/s

What is the number of atoms of hydrogen in 34 g of ammonia gas (NH₃)? The relative atomic mass of hydrogen is 1 g·mol⁻¹, the relative atomic mass of nitrogen is 14 g·mol⁻¹.

• 5.0 × 10²³

• 3.0 × 10²³

• 3.6 × 10²⁴

• 4.0 × 10²³