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Ch.10 - Gases
Chapter 10, Problem 81b

(b) Calculate the rms speed of NF3 molecules at 25 °C.

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Identify the formula for the root mean square (rms) speed: \( v_{\text{rms}} = \sqrt{\frac{3RT}{M}} \), where \( R \) is the ideal gas constant, \( T \) is the temperature in Kelvin, and \( M \) is the molar mass in kg/mol.
Convert the given temperature from Celsius to Kelvin by adding 273.15 to the Celsius temperature.
Determine the molar mass of NF<sub>3</sub> by adding the atomic masses of nitrogen (N) and fluorine (F) from the periodic table: \( M = M_N + 3 \times M_F \).
Convert the molar mass from grams per mole to kilograms per mole by dividing by 1000.
Substitute the values of \( R \), \( T \), and \( M \) into the rms speed formula and solve for \( v_{\text{rms}} \).

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Key Concepts

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

Root Mean Square (RMS) Speed

The root mean square speed is a measure of the average speed of particles in a gas. It is calculated using the formula v_rms = sqrt(3RT/M), where R is the ideal gas constant, T is the temperature in Kelvin, and M is the molar mass of the gas in kg/mol. This concept is crucial for understanding the kinetic energy and behavior of gas molecules.
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Ideal Gas Law

The ideal gas law relates the pressure, volume, temperature, and number of moles of a gas through the equation PV = nRT. This law assumes that gas molecules do not interact and occupy no volume, which simplifies calculations involving gas properties. Understanding this law is essential for deriving the RMS speed in the context of gas behavior.
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Temperature Conversion

Temperature must be expressed in Kelvin for calculations in thermodynamics and gas laws. To convert Celsius to Kelvin, add 273.15 to the Celsius temperature. This conversion is necessary when calculating RMS speed, as the temperature directly influences the kinetic energy and speed of gas molecules.
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Related Practice
Textbook Question

Suppose you have two 1-L flasks, one containing N2 at STP, the other containing CH4 at STP. How do these systems compare with respect to (a) number of molecules?

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Textbook Question

Suppose you have two 1-L flasks, one containing N2 at STP, the other containing CH4 at STP. How do these systems compare with respect to (b) density?

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Textbook Question

Suppose you have two 1-L flasks, one containing N2 at STP, the other containing CH4 at STP. How do these systems compare with respect to (c) average kinetic energy of the molecules?

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Textbook Question

(c) Calculate the most probable speed of an ozone molecule in the stratosphere, where the temperature is 270 K.

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Textbook Question

Which one or more of the following statements are true? (a) O2 will effuse faster than Cl2. (b) Effusion and diffusion are different names for the same process. (c) Perfume molecules travel to your nose by the process of effusion. (d) The higher the density of a gas, the shorter the mean free path.

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Textbook Question

At constant pressure, the mean free path 1l2 of a gas molecule is directly proportional to temperature. At constant temperature, l is inversely proportional to pressure. If you compare two different gas molecules at the same temperature and pressure, l is inversely proportional to the square of the diameter of the gas molecules. Put these facts together to create a formula for the mean free path of a gas molecule with a proportionality constant (call it Rmfp, like the ideal-gas constant) and define units for Rmfp.

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