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\(\bullet$$\bullet\) A flask contains a mixture of neon (Ne), krypton (Kr), and radon \((\mathrm{Rn})\) gases. Compare (a) the average kinetic energies of the three types of atoms; (b) their root-mean-square speeds. (Hint: The periodic table in Appendix C shows the molar mass (in \(\mathrm{g} / \mathrm{mol}\) ) of each element.)

Short Answer

Expert verified
(a) All have the same average kinetic energy. (b) Ne has the highest and Rn has the lowest root-mean-square speed.

Step by step solution

01

Understand the Kinetic Energy of Gas Particles

The average kinetic energy for a gas particle is given by the equation \( KE = \frac{3}{2}kT \), where \( k \) is the Boltzmann constant, and \( T \) is the temperature in Kelvin. Note that this equation is solely dependent on temperature, not the type of gas.
02

Assess Average Kinetic Energies

Since the equation \( KE = \frac{3}{2}kT \) is independent of the type of gas, all three types of gases in the flask (Ne, Kr, Rn) have the same average kinetic energy, provided they are at the same temperature.
03

Calculate Root-Mean-Square Speed Formula

The root-mean-square speed \( v_{rms} \) can be calculated using \( v_{rms} = \sqrt{\frac{3kT}{m}} \) where \( k \) is the Boltzmann constant, \( T \) is temperature in Kelvin, and \( m \) is the mass of the gas particle.
04

Convert Molar Mass to Kilograms for Calculation

Look up the molar mass of each gas: Ne (20.18 g/mol), Kr (83.8 g/mol), Rn (222 g/mol). Convert these to kilograms: Ne (0.02018 kg/mol), Kr (0.0838 kg/mol), Rn (0.222 kg/mol).
05

Compare Root-Mean-Square Speeds

Calculate the \( v_{rms} \) for each gas using their converted molar masses and the equation \( v_{rms} = \sqrt{\frac{3kT}{m}} \). Since \( m \) is in the denominator, gases with lower masses (Ne) will have higher \( v_{rms} \) compared to heavier gases (Kr, Rn). Therefore, \( v_{rms, Ne} > v_{rms, Kr} > v_{rms, Rn} \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Average Kinetic Energy
The average kinetic energy of gas particles is a key concept in the kinetic theory of gases. It relates directly to the temperature of the gas. Given by the formula \( KE = \frac{3}{2}kT \), this equation tells us that the average kinetic energy (KE) depends only on the absolute temperature (\(T\)) of the system. Here, \(k\) is known as the Boltzmann constant, a fundamental constant in physics.

An important implication of this formula is that the average kinetic energy does not depend on the type of gas particle. Whether you have neon, krypton, or radon in a flask, as long as they are at the same temperature, they will each have the same average kinetic energy. This is because the equation is "blind" to changes in the particle type or mass. Understanding this helps in studying gas behavior and making predictions about how different gases will react under similar conditions.
Root-Mean-Square Speed
The root-mean-square (RMS) speed is a measure to understand how fast gas particles are moving. It provides a statistical speed value that considers varying speeds of particles within a gas. The formula to calculate the root-mean-square speed is \( v_{rms} = \sqrt{\frac{3kT}{m}} \).

This formula is similar to the average kinetic energy equation but with a critical difference: it includes the particle's mass (m) in the calculation. The numerator, \(3kT\), remains constant for a given temperature, but as the mass increases, the RMS speed decreases. Thus, - Lower molar mass gases, like neon, will have higher RMS speeds.- Heavier gases like krypton and radon will have lower RMS speeds compared to lighter gases when at the same temperature.This means in a mixed gas environment, lighter atoms move faster than heavier ones. This knowledge can be applied in practical applications like gas diffusion and effusion.
Gas Particle Molar Mass
The molar mass of a gas particle is a crucial factor affecting its behavior according to the kinetic theory of gases. It refers to the mass of one mole of a gas particle and is typically expressed in grams per mole (g/mol). In the context of calculating the root-mean-square speed of gas particles, knowing the molar mass is vital because it must be converted into kilograms per mole (kg/mol) to ensure consistent units in the equation \( v_{rms} = \sqrt{\frac{3kT}{m}} \).

Here's why molar mass matters:- Lighter gases (those with a smaller molar mass) will have higher RMS speeds because the denominator \(m\) in the RMS speed equation is smaller.- Heavier gases, with larger molar masses, translate to lower speeds at the same temperature.For instance, comparing the molar masses of neon (20.18 g/mol), krypton (83.8 g/mol), and radon (222 g/mol), it's clear that neon will move the fastest and radon the slowest, because the lighter the gas particle, the faster it moves according to its kinetic properties.

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Most popular questions from this chapter

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