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Ch.10 - Gases
Chapter 10, Problem 82c2

(c) Calculate the most probable speeds of Cl2 molecules at 300 K.

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Identify the formula for the most probable speed of a gas molecule, which is given by \( v_p = \sqrt{\frac{2kT}{m}} \), where \( v_p \) is the most probable speed, \( k \) is the Boltzmann constant, \( T \) is the temperature in Kelvin, and \( m \) is the mass of a single molecule.
Convert the molar mass of \( \text{Cl}_2 \) from grams per mole to kilograms per molecule. The molar mass of \( \text{Cl}_2 \) is approximately 70.9 g/mol. Use Avogadro's number \( 6.022 \times 10^{23} \) to find the mass of one molecule.
Substitute the values into the formula: \( k = 1.38 \times 10^{-23} \text{ J/K} \), \( T = 300 \text{ K} \), and the calculated mass of a \( \text{Cl}_2 \) molecule.
Calculate the expression under the square root to find the most probable speed.
Ensure the units are consistent throughout the calculation to obtain the speed in meters per second (m/s).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Kinetic Molecular Theory

Kinetic Molecular Theory explains the behavior of gases in terms of particles in constant motion. It posits that the temperature of a gas is directly related to the average kinetic energy of its molecules. This theory helps in understanding how temperature influences the speed of gas molecules, which is crucial for calculating the most probable speed.
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Most Probable Speed

The most probable speed of gas molecules is the speed at which the largest number of molecules are moving at a given temperature. It can be calculated using the formula v_mp = sqrt(2kT/m), where v_mp is the most probable speed, k is the Boltzmann constant, T is the temperature in Kelvin, and m is the mass of a molecule. This concept is essential for determining the speed of Cl2 molecules at 300 K.
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Most Probable Speed Example

Molar Mass and Gas Constant

Molar mass is the mass of one mole of a substance, which is critical for converting between grams and moles in calculations. For Cl2, the molar mass is approximately 70.9 g/mol. The gas constant (R) is used in various gas equations and relates to the behavior of gases under different conditions, aiding in the calculation of molecular speeds.
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