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Chapter 3: Problem 34

What does it mean to say a reactant is present "in excess" in a process? Can the limiting reactant be present in excess? Does the presence of an excess of a reactant affect the mass of products expected for a reaction?

Short Answer

Expert verified
A reactant is present "in excess" when it is provided in a greater amount than required to react completely with the other reaction components. The limiting reactant, which cannot be in excess, is the reactant consumed entirely during the reaction, determining the maximum amount of product formed. The presence of excess reactants doesn't directly affect the mass of products expected for the reaction, which is determined by stoichiometry and limiting reactant, but may indirectly impact real-life scenarios through factors like reaction rates or equilibrium state.

Step by step solution

01

Definition of Reactant in Excess

A reactant is said to be present "in excess" when it is provided in a greater amount than what is required to react completely with the other reactants involved in the reaction. In a chemical reaction, one reactant may be used up before the others, causing the reaction to stop. The reactant that is completely consumed and determines the amount of product formed is called the limiting reactant. The other reactants, which are not fully consumed, are said to be present in excess.
02

Limiting Reactant and Excess

No, the limiting reactant cannot be present in excess. By definition, the limiting reactant is the one that is consumed entirely during the course of the reaction and determines the maximum amount of product formed. Therefore, the limiting reactant cannot be present in amounts greater than what is required to react completely with the other reactants.
03

Excess Reactant and Mass of Products

The presence of an excess of a reactant does not affect the mass of products expected for a reaction directly. The mass of the products is determined by the stoichiometry of the reaction and the amount of the limiting reactant. Once the limiting reactant is entirely consumed, no more product can be formed even if there is an excess of the other reactants present. However, an excess of reactants might indirectly affect the mass of products in real-life scenarios by affecting factors such as the reaction rates or equilibrium state of the reaction.

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Most popular questions from this chapter

Nitric acid is produced commercially by the Ostwald process, represented by the following equations: $$ \begin{aligned} 4 \mathrm{NH}_{3}(g)+5 \mathrm{O}_{2}(g) & \longrightarrow 4 \mathrm{NO}(g)+6 \mathrm{H}_{2} \mathrm{O}(g) \\ 2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) & \longrightarrow 2 \mathrm{NO}_{2}(g) \\ 3 \mathrm{NO}_{2}(g)+\mathrm{H}_{2} \mathrm{O}(l) & \longrightarrow 2 \mathrm{HNO}_{3}(a q)+\mathrm{NO}(g) \end{aligned} $$ What mass of \(\mathrm{NH}_{3}\) must be used to produce \(1.0 \times 10^{6} \mathrm{~kg}\) \(\mathrm{HNO}_{3}\) by the Ostwald process? Assume \(100 \%\) yield in each reaction, and assume that the NO produced in the third step is not recycled.

A compound contains only carbon, hydrogen, nitrogen, and oxygen. Combustion of \(0.157 \mathrm{~g}\) of the compound produced \(0.213 \mathrm{~g} \mathrm{CO}_{2}\) and \(0.0310 \mathrm{~g} \mathrm{H}_{2} \mathrm{O} .\) In another experiment, it is found that \(0.103 \mathrm{~g}\) of the compound produces \(0.0230 \mathrm{~g} \mathrm{NH}_{3} .\) What is the empirical formula of the compound? Hint: Combustion involves reacting with excess \(\mathrm{O}_{2}\). Assume that all the carbon ends up in \(\mathrm{CO}_{2}\) and all the hydrogen ends up in \(\mathrm{H}_{2} \mathrm{O}\). Also assume that all the nitrogen ends up in the \(\mathrm{NH}_{3}\) in the second experiment.

Ascorbic acid, or vitamin \(\mathrm{C}\left(\mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{6}\right)\), is an essential vitamin. It cannot be stored by the body and must be present in the diet. What is the molar mass of ascorbic acid? Vitamin C tablets are taken as a dietary supplement. If a typical tablet contains \(500.0 \mathrm{mg}\) vitamin \(\mathrm{C}\), what amount (moles) and what number of molecules of vitamin C does it contain?

An element \(\mathrm{X}\) forms both a dichloride \(\left(\mathrm{XCl}_{2}\right)\) and a tetrachloride \(\left(\mathrm{XCl}_{4}\right)\). Treatment of \(10.00 \mathrm{~g} \mathrm{XCl}_{2}\) with excess chlorine forms \(12.55 \mathrm{~g} \mathrm{XCl}_{4}\). Calculate the atomic mass of \(\mathrm{X}\), and identify \(\mathrm{X}\).

In the production of printed circuit boards for the electronics industry, a \(0.60\) -mm layer of copper is laminated onto an insulating plastic board. Next, a circuit pattern made of a chemically resistant polymer is printed on the board. The unwanted copper is removed by chemical etching, and the protective polymer is finally removed by solvents. One etching reaction is $$\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}(a q)+4 \mathrm{NH}_{3}(a q)+\mathrm{Cu}(s) \longrightarrow 2 \mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}(a q)$$ A plant needs to manufacture 10,000 printed circuit boards, each \(8.0 \times 16.0 \mathrm{~cm}\) in area. An average of \(80 . \%\) of the copper is removed from each board (density of copper \(=8.96 \mathrm{~g} / \mathrm{cm}^{3}\) ). What masses of \(\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}\) and \(\mathrm{NH}_{3}\) are needed to do this? Assume \(100 \%\) yield.
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