Helium-neon (HeNe)lasers contain a low-pressure mixture of He and Ne gases.How many times greater is the root-mean-square speed of He atoms than Ne atoms in a HeNe laser?

Question

Quizplus · Accepted Answer

The root-mean-square speed of a gas is given by the formula v = √(3kT/m), where k is Boltzmann constant, T is the temperature, and m is the mass of the gas particle. Since He and Ne have different atomic masses but are at the same temperature, their root-mean-square speeds will be different. The ratio of their speeds can be found as follows:

v(He) / v(Ne) = √(m(Ne) / m(He))
We can look up the masses of He and Ne and find:

v(He) / v(Ne) = √(20.18 / 4.00) = 2.24
Therefore, the speed of He atoms is 2.24 times greater than that of Ne atoms. Rounded to one significant figure, the answer is 2.2, so the correct choice is C).

Helium-Neon (HeNe)lasers Contain a Low-Pressure Mixture of He and Ne