Question

Calculate the average kinetic energies of \(\mathrm{CH}_{4}(g)\) and \(\mathrm{N}_{2}(g)\) molecules at \(273 \mathrm{~K}\) and \(546 \mathrm{~K}\).

Short answer

The average kinetic energies for CH4(g) and N2(g) at 273K and 546K are as follows: - For CH4 molecule at 273K: \(KE_{avg} = 5.65 \times 10^{-21} J\) - For CH4 molecule at 546K: \(KE_{avg} = 1.13 \times 10^{-20} J\) - For N2 molecule at 273K: \(KE_{avg} = 5.65 \times 10^{-21} J\) - For N2 molecule at 546K: \(KE_{avg} = 1.13 \times 10^{-20} J\)

Step-by-step solution

Identify the Temperature Values

We are given two temperature values, 273K and 546K. We will calculate the average kinetic energies for CH4 and N2 at these temperatures.

Calculate the Average Kinetic Energy for CH4 at 273K

Using the formula for calculating average kinetic energy, we can determine the average kinetic energy for CH4 at 273K: \(KE_{avg} = \dfrac{3}{2} k_B T \) \(KE_{avg(CH4, 273K)} = \dfrac{3}{2} (1.38 \times 10^{-23}\,\cancel{J\,K^{-1}}) (273\,\cancel{K}) \) \(KE_{avg(CH4, 273K)} = 5.65 \times 10^{-21} J\)

Calculate the Average Kinetic Energy for CH4 at 546K

Using the same formula, we can determine the average kinetic energy for CH4 at 546K: \(KE_{avg} = \dfrac{3}{2} k_B T \) \(KE_{avg(CH4, 546K)} = \dfrac{3}{2} (1.38 \times 10^{-23}\,\cancel{J\,K^{-1}}) (546\,\cancel{K}) \) \(KE_{avg(CH4, 546K)} = 1.13 \times 10^{-20} J\)

Calculate the Average Kinetic Energy for N2 at 273K

Using the formula for calculating average kinetic energy, we can determine the average kinetic energy for N2 at 273K: \(KE_{avg} = \dfrac{3}{2} k_B T \) \(KE_{avg(N2, 273K)} = \dfrac{3}{2} (1.38 \times 10^{-23}\,\cancel{J\,K^{-1}}) (273\,\cancel{K}) \) \(KE_{avg(N2, 273K)} = 5.65 \times 10^{-21} J\)

Calculate the Average Kinetic Energy for N2 at 546K

Using the same formula, we can determine the average kinetic energy for N2 at 546K: \(KE_{avg} = \dfrac{3}{2} k_B T \) \(KE_{avg(N2, 546K)} = \dfrac{3}{2} (1.38 \times 10^{-23}\,\cancel{J\,K^{-1}}) (546\,\cancel{K}) \) \(KE_{avg(N2, 546K)} = 1.13 \times 10^{-20} J\) Now we have calculated the average kinetic energies for both CH4(g) and N2(g) at 273K and 546K: - For CH4 molecule at 273K: \(KE_{avg} = 5.65 \times 10^{-21} J\) - For CH4 molecule at 546K: \(KE_{avg} = 1.13 \times 10^{-20} J\) - For N2 molecule at 273K: \(KE_{avg} = 5.65 \times 10^{-21} J\) - For N2 molecule at 546K: \(KE_{avg} = 1.13 \times 10^{-20} J\)

Key concepts

Kinetic Molecular Theory

The kinetic molecular theory is a cornerstone in the understanding of gas behaviors. It states that gases are composed of a large number of particles that are in constant, random motion. These gas molecules collide with each other and the walls of their container without losing energy in elastic collisions. The theory helps us determine the relationship between the macroscopic properties of gases, such as pressure and temperature, and the microscopic behaviors of the gas molecules themselves.

According to this theory, the temperature of a gas is proportional to the average kinetic energy of its molecules. This implies that if we increase the temperature of a gas, its molecules will move faster and, as a result, the average kinetic energy will also increase. The converse is true; a lower temperature means slower molecular motion and lower average kinetic energy.

Gas Molecules Kinetic Energy

The kinetic energy of gas molecules is the energy associated with their motion. Each individual molecule possesses translational kinetic energy as it moves in three-dimensional space. While these molecules have varying speeds, what we measure in thermodynamics is the average kinetic energy of the gas molecules. The faster they move, the greater their kinetic energy.

When calculating the average kinetic energy of gas molecules, we use the formula expressed during the exercise:\[\begin{equation}KE_{avg} = \frac{3}{2} k_B T \end{equation}\]This equation highlights that average kinetic energy is directly dependent on the absolute temperature of the gas. Thus, kinetic energy serves as a microscopic indicator of the gas's temperature.

Temperature and Kinetic Energy

There is a direct and proportional relationship between temperature and the kinetic energy of gas molecules. As temperature increases, the kinetic energy of the gas molecules also increases. This is due to the fact that temperature is a measure of the average kinetic energy of the particles in a substance.

It is crucial to note that temperature is measured on an absolute scale, such as Kelvin, where 0 K is absolute zero, the point at which particles theoretically stop moving. The step-by-step solution given for different temperatures, such as 273 K and 546 K, shows how the kinetic energy of molecules changes with the temperature. The results reveal that the average kinetic energy doubles when the temperature is doubled, demonstrating the direct proportionality between these two variables.

Boltzmann Constant

The Boltzmann constant (\[\begin{equation}k_B\end{equation}\]) is a fundamental physical constant that serves as a bridge between macroscopic and microscopic physics. It appears in the equation that relates the average kinetic energy of particles to temperature, reflecting the individual components' energies on the molecular scale.

The value of the Boltzmann constant is approximately \[\begin{equation}1.38 \times 10^{-23} J/K\end{equation}\], where J represents joules and K represents Kelvin. As indicated in the exercise, when we use the Boltzmann constant in our calculations, we can quantify the average kinetic energy per molecule in a gas. It is important to realize that this constant is a significant part of the ideal gas law and the kinetic molecular theory, providing an essential link between the temperature of a gas and the average kinetic energy of its molecules.