Ch.3 - Chemical Reactions and Reaction Stoichiometry

Problem 103

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Chapter 3, Problem 103

A mixture of N21g2 and H21g2 reacts in a closed container to form ammonia, NH31g2. The reaction ceases before either reactant has been totally consumed. At this stage 3.0 mol N2, 3.0 mol H2, and 3.0 mol NH3 are present. How many moles of N2 and H2 were present originally?

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insert step 1> Write the balanced chemical equation for the reaction: N_2(g) + 3H_2(g) \rightarrow 2NH_3(g).

insert step 2> Use the stoichiometry of the reaction to set up relationships between the moles of reactants and products. For every 1 mole of N_2, 3 moles of H_2 are required to produce 2 moles of NH_3.

insert step 3> Let x be the initial moles of N_2 and y be the initial moles of H_2.

insert step 4> Set up the equations based on the stoichiometry and the information given: x - a = 3.0 (moles of N_2 remaining), y - 3a = 3.0 (moles of H_2 remaining), and 2a = 3.0 (moles of NH_3 formed).

insert step 5> Solve the system of equations to find the initial moles of N_2 (x) and H_2 (y).

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Key Concepts

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

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It allows us to calculate the amounts of substances consumed and produced in a reaction based on balanced chemical equations. In this case, understanding the stoichiometric ratios of nitrogen (N2), hydrogen (H2), and ammonia (NH3) is essential to determine the original amounts of reactants.

Limiting Reactant

The limiting reactant is the substance that is completely consumed in a chemical reaction, thus determining the maximum amount of product that can be formed. In this scenario, identifying which reactant (N2 or H2) limits the formation of NH3 is crucial for calculating the initial moles of each reactant. The limiting reactant concept helps in understanding how much of each reactant was present before the reaction reached equilibrium.

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 this problem, the reaction between N2 and H2 to form NH3 reaches a point where the amounts of all species remain unchanged. Recognizing that the reaction has not gone to completion but has reached a state of equilibrium is vital for determining the initial amounts of N2 and H2.

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Textbook Question

A method used by the U.S. Environmental Protection Agency (EPA) for determining the concentration of ozone in air is to pass the air sample through a 'bubbler' containing sodium iodide, which removes the ozone according to the following equation: O31g2 + 2 NaI1aq2 + H2O1l2¡ O21g2 + I21s2 + 2 NaOH1aq2 (b) How many grams of sodium iodide are needed to remove 1.3 mg of O3?

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Textbook Question

The fat stored in a camel's hump is a source of both energy and water. Calculate the mass of H2O produced by the metabolism of 1.0 kg of fat, assuming the fat consists entirely of tristearin 1C57H110O62, a typical animal fat, and assuming that during metabolism, tristearin reacts with O2 to form only CO2 and H2O.

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Open Question

When hydrocarbons are burned in a limited amount of air, both CO and CO2 form. When 0.450 g of a particular hydrocarbon was burned in air, 0.467 g of CO, 0.733 g of CO2, and 0.450 g of H2O were formed. (a) What is the empirical formula of the compound? (b) How many grams of O2 were used in the reaction? (c) How many grams would have been required for complete combustion?

Textbook Question

A mixture containing KClO3, K2CO3, KHCO3, and KCl was heated, producing CO2, O2, and H2O gases according to the following equations: 2 KClO31s2¡2 KCl1s2 + 3 O21g2 2 KHCO31s2¡K2O1s2 + H2O1g2 + 2 CO21g2 K2CO31s2¡K2O1s2 + CO21g2 The KCl does not react under the conditions of the reaction. If 100.0 g of the mixture produces 1.80 g of H2O, 13.20 g of CO2, and 4.00 g of O2, what was the composition of the original mixture? (Assume complete decomposition of the mixture.) How many grams of K2CO3 were in the original mixture?

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Open Question

Boron nitride, BN, is an electrical insulator with remarkable thermal and chemical stability. Its density is 2.1 g/cm3. It can be made by reacting boric acid, H3BO3, with ammonia. The other product of the reaction is water. (b) If you made 225 g of boric acid react with 150 g of ammonia, what mass of BN could you make? (d) One application of BN is as a thin film for electrical insulation. If you take the mass of BN from part (b) and make a 0.4 mm thin film from it, what area, in cm2, would it cover?

Textbook Question

Viridicatumtoxin B, C30H31NO10, is a natural antibiotic compound. It requires a synthesis of 12 steps in the laboratory. Assuming all steps have equivalent yields of 85%, which is the final percent yield of the total synthesis?

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