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Ch.15 - Chemical Equilibrium
Chapter 15, Problem 76b

A sample of nitrosyl bromide (NOBr) decomposes according to the equation 2 NOBr(𝑔) ⇌ 2 NO(𝑔) + Br2(𝑔) An equilibrium mixture in a 5.00-L vessel at 100°C contains 3.22 g of NOBr, 3.08 g of NO, and 4.19 g of Br2. (b) What is the total pressure exerted by the mixture of gases?

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1
Calculate the number of moles of each gas present in the mixture using the formula: number of moles (n) = mass (g) / molar mass (g/mol). The molar masses are: NOBr = 106.92 g/mol, NO = 30.01 g/mol, Br<sub>2</sub> = 159.808 g/mol.
Use the ideal gas law to find the total number of moles of gas in the vessel. The ideal gas law is PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the gas constant (0.0821 L·atm/mol·K), and T is the temperature in Kelvin.
Convert the temperature from Celsius to Kelvin by adding 273.15 to the Celsius temperature.
Calculate the total pressure using the ideal gas law rearranged to solve for P: P = (nRT) / V. Substitute the total number of moles calculated, the gas constant, the temperature in Kelvin, and the volume of the vessel.
Ensure all units are consistent when substituting values into the ideal gas law equation to calculate the pressure in atmospheres.

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Key Concepts

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

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 is essential for calculating the total pressure of a gas mixture, as it allows us to determine how the quantities of gases present affect the overall pressure in a given volume.
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Molar Mass and Mass to Moles Conversion

To find the total pressure exerted by the gas mixture, it is necessary to convert the mass of each gas into moles using their respective molar masses. This conversion is crucial because the Ideal Gas Law requires the number of moles (n) to calculate pressure, making it a fundamental step in solving the problem.
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Dalton's Law of Partial Pressures

Dalton's Law states that the total pressure of a gas mixture is equal to the sum of the partial pressures of each individual gas. This principle is important for determining the total pressure in the vessel, as it allows us to calculate the contribution of each gas based on its mole fraction and the total number of moles present.
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Related Practice
Textbook Question

When 2.00 mol of SO2Cl2 is placed in a 2.00-L flask at 303 K, 56% of the SO2Cl2 decomposes to SO2 and Cl2: SO2Cl2(g) ⇌ SO2(g) + Cl2(g) (c) According to Le Châtelier's principle, would the percent of SO2Cl2 that decomposes increase, decrease or stay the same if the mixture were transferred to a 15.00-L vessel?

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Open Question
The value of the equilibrium constant Kc for the reaction N2(g) + 3 H2(g) ⇌ 2 NH3(g) changes in the following manner as a function of temperature: Temperature (°C) Kc 300 9.6 400 0.50 500 0.058. (b) Use the standard enthalpies of formation given in Appendix C to determine the ΔH for this reaction at standard conditions. Does this value agree with your prediction from part (a)?
Open Question
A sample of nitrosyl bromide (NOBr) decomposes according to the equation 2 NOBr(g) ⇌ 2 NO(g) + Br2(g). An equilibrium mixture in a 5.00-L vessel at 100 _x001F_C contains 3.22 g of NOBr, 3.08 g of NO, and 4.19 g of Br2. (a) Calculate Kc.
Textbook Question

A sample of nitrosyl bromide (NOBr) decomposes according to the equation 2 NOBr(g) ⇌ 2 NO(g) + Br2(g) An equilibrium mixture in a 5.00-L vessel at 100°C contains 3.22 g of NOBr, 3.08 g of NO, and 4.19 g of Br2. (c) What was the mass of the original sample of NOBr?

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Open Question
Consider the hypothetical reaction A1g2 Δ 2 B1g2. A flask is charged with 0.75 atm of pure A, after which it is allowed to reach equilibrium at 0 _x001F_C. At equilibrium, the partial pressure of A is 0.36 atm. (a) What is the total pressure in the flask at equilibrium?
Open Question

Consider the hypothetical reaction A(g) ⇌ 2 B(g). A flask is charged with 0.75 atm of pure A, after which it is allowed to reach equilibrium at 0°C. At equilibrium, the partial pressure of A is 0.36 atm. (a) What is the total pressure in the flask at equilibrium?