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Ch.15 - Chemical Equilibrium
All textbooksBrown 15th EditionCh.15 - Chemical EquilibriumProblem 76c
Chapter 15, Problem 76c

A sample of nitrosyl bromide (NOBr) decomposes according to the equation 2 NOBr(𝑔) β‡Œ 2 NO(𝑔) + Br2(𝑔) An equilibrium mixture in a 5.00-L vessel at 100Β°C contains 3.22 g of NOBr, 2.46 g of NO, and 6.55 g of Br2. (c) What was the mass of the original sample of NOBr?

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1
Calculate the molar mass of NOBr using the atomic masses of nitrogen (N), oxygen (O), and bromine (Br).
Convert the given mass of NOBr at equilibrium (3.22 g) to moles using its molar mass.
Convert the given masses of NO (2.46 g) and Br_2 (6.55 g) to moles using their respective molar masses.
Use the stoichiometry of the balanced equation to determine the moles of NOBr that decomposed, based on the moles of NO and Br_2 formed.
Add the moles of NOBr at equilibrium to the moles of NOBr that decomposed to find the initial moles of NOBr, then convert this back to grams to find the original mass of the sample.

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Key Concepts

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

Chemical Equilibrium

Chemical equilibrium occurs when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. In the case of the decomposition of nitrosyl bromide (NOBr), the equilibrium expression can be used to relate the concentrations of NOBr, NO, and Br2 at a given temperature, which is essential for understanding the system's behavior.
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Stoichiometry

Stoichiometry involves the calculation of reactants and products in chemical reactions based on balanced equations. For the reaction 2 NOBr β‡Œ 2 NO + Br2, the stoichiometric coefficients indicate the molar ratios of the substances involved, which are crucial for determining the amounts of reactants and products at equilibrium and for calculating the original mass of NOBr.
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Molar Mass and Mass-to-Moles Conversion

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole. To find the original mass of NOBr, it is necessary to convert the mass of the products (NO and Br2) back to moles using their respective molar masses, and then apply stoichiometry to relate these moles back to the original amount of NOBr before decomposition.
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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) β‡Œ SO2(g) + Cl2(g) (c) According to Le ChΓ’telier'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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Textbook Question

A sample of nitrosyl bromide (NOBr) decomposes according to the equation 2 NOBr(𝑔) β‡Œ 2 NO(𝑔) + Br2(𝑔) An equilibrium mixture in a 5.00-L vessel at 100Β°C contains 3.22 g of NOBr, 2.46 g of NO, and 6.55 g of Br2. (b) What is the total pressure exerted by the mixture of gases?

Textbook Question

Consider the hypothetical reaction A(𝑔) β‡Œ 2 B(𝑔). A flask is charged with 0.75 atm of pure A, after which it is allowed to reach equilibrium at 0Β°C. At equilibrium, the partial pressure of A is 0.36 atm. (c) To maximize the yield of product B, would you make the reaction flask larger or smaller?

Textbook Question

As shown in Table 15.2, the equilibrium constant for the reaction N2(g) + 3 H2(g) β‡Œ 2 NH3(g) is Kp = 4.34 Γ— 10-3 at 300Β°C. Pure NH3 is placed in a 1.00-L flask and allowed to reach equilibrium at this temperature. There are 1.05 g NH3 in the equilibrium mixture. (b) What was the initial mass of ammonia placed in the vessel?

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