Ch.3 - Chemical Reactions and Reaction Stoichiometry

Problem 115b

Chapter 3, Problem 115b

The thermite reaction, Fe₂O₃ + Al → Al₂O₃ + Fe produces so much heat that the Fe product melts. This reaction is used industrially to weld metal parts under water, where a torch cannot be employed. It is also a favorite chemical demonstration in the lecture hall (on a small scale). (b) Calculate how many grams of aluminum are needed to completely react with 500.0 g of Fe₂O₃ in this reaction.

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Write the balanced chemical equation for the thermite reaction: \( \text{Fe}_2\text{O}_3 + 2\text{Al} \rightarrow \text{Al}_2\text{O}_3 + 2\text{Fe} \).

Calculate the molar mass of \( \text{Fe}_2\text{O}_3 \) using the atomic masses of Fe and O.

Determine the number of moles of \( \text{Fe}_2\text{O}_3 \) in 500.0 g by dividing the mass by its molar mass.

Use the stoichiometry of the balanced equation to find the moles of Al needed. According to the equation, 1 mole of \( \text{Fe}_2\text{O}_3 \) reacts with 2 moles of Al.

Calculate the mass of Al required by multiplying the moles of Al by the molar mass of Al.

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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 chemists to calculate how much of each substance is needed or produced based on balanced chemical equations. In the thermite reaction, understanding stoichiometry is essential to determine the amount of aluminum required to react with a given mass of iron(III) oxide.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is crucial for converting between the mass of a substance and the number of moles, which is necessary for stoichiometric calculations. For the thermite reaction, knowing the molar masses of Fe2O3 and Al allows for accurate calculations of how much aluminum is needed to react with 500.0 g of iron(III) oxide.

Balanced Chemical Equation

A balanced chemical equation represents a chemical reaction with equal numbers of each type of atom on both sides of the equation. This balance is essential for applying stoichiometry, as it indicates the exact proportions of reactants and products involved. In the thermite reaction, the balanced equation Fe2O3 + 2Al → Al2O3 + 2Fe shows that two moles of aluminum are required for every mole of iron(III) oxide, guiding the calculation of aluminum needed.

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Textbook Question

The source of oxygen that drives the internal combustion engine in an automobile is air. Air is a mixture of gases, principally N₂(79%) and O₂(20%). In the cylinder of an automobile engine, nitrogen can react with oxygen to produce nitric oxide gas, NO. As NO is emitted from the tailpipe of the car, it can react with more oxygen to produce nitrogen dioxide gas. (b) Both nitric oxide and nitrogen dioxide are pollutants that can lead to acid rain and global warming; collectively, they are called 'NOx' gases. In 2009, the United States emitted an estimated 19 million tons of nitrogen dioxide into the atmosphere. How many grams of nitrogen dioxide is this?

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Textbook Question

The source of oxygen that drives the internal combustion engine in an automobile is air. Air is a mixture of gases, principally N₂(79%) and O₂(20%). In the cylinder of an automobile engine, nitrogen can react with oxygen to produce nitric oxide gas, NO. As NO is emitted from the tailpipe of the car, it can react with more oxygen to produce nitrogen dioxide gas. (c) The production of NOx gases is an unwanted side reaction of the main engine combustion process that turns octane, C₈H₁₈, into CO₂ and water. If 85% of the oxygen in an engine is used to combust octane and the remainder used to produce nitrogen dioxide, calculate how many grams of nitrogen dioxide would be produced during the combustion of 500 g of octane.

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Textbook Question

The thermite reaction, Fe2O3 + Al S Al2O3 + Fe produces so much heat that the Fe product melts. This reaction is used industrially to weld metal parts under water, where a torch cannot be employed. It is also a favorite chemical demonstration in the lecture hall (on a small scale). (d) If you performed the reverse reaction— aluminum oxide plus iron makes iron oxide plus aluminum—would that reaction have heat as a reactant or a product?

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Textbook Question

One of the most bizarre reactions in chemistry is called the Ugi reaction: R1C(=O)R2 + R3 - NH2 + R4COOH + R5NC S R4C(=O)N(R3)C(R1R2)C=ONHR5 + H2O

(a) Write out the balanced chemical equation for the Ugi reaction, for the case where R = CH3CH2CH2CH2CH2CH2— (this is called the hexyl group) for all compounds.

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