Ch.3 - Chemical Reactions and Reaction Stoichiometry

Problem 115c

Chapter 3, Problem 115c

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). (c) This reaction produces 852 kJ of heat per mole of Fe₂O₃ reacted. How many grams of Fe₂O₃ are needed to produce 1.00 × 10⁴ kJ of heat?

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Identify the given information: The reaction produces 852 kJ of heat per mole of Fe2O3 reacted, and we need to produce 1.00 × 10^4 kJ of heat.

Set up a proportion to find the number of moles of Fe2O3 needed: \( \frac{1 \text{ mole of Fe2O3}}{852 \text{ kJ}} = \frac{x \text{ moles of Fe2O3}}{1.00 \times 10^4 \text{ kJ}} \). Solve for \( x \).

Calculate the number of moles of Fe2O3 required using the proportion: \( x = \frac{1.00 \times 10^4 \text{ kJ}}{852 \text{ kJ/mole}} \).

Determine the molar mass of Fe2O3. The molar mass is calculated by adding the atomic masses of 2 Fe atoms and 3 O atoms: \( 2 \times 55.85 \text{ g/mol} + 3 \times 16.00 \text{ g/mol} \).

Convert the moles of Fe2O3 to grams using the molar mass: \( \text{grams of Fe2O3} = \text{moles of Fe2O3} \times \text{molar mass of Fe2O3} \).

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Key Concepts

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

Thermochemical Equations

Thermochemical equations represent the heat changes associated with chemical reactions. They indicate the amount of heat released or absorbed during a reaction, typically expressed in kilojoules per mole. Understanding these equations is crucial for calculating the energy changes in reactions, such as the thermite reaction, where a specific amount of heat is produced per mole of reactant.

Stoichiometry

Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. It allows us to calculate the amounts of substances consumed and produced based on balanced chemical equations. In the context of the thermite reaction, stoichiometry helps determine how many grams of Fe2O3 are needed to produce a desired amount of heat, using the molar mass and the heat produced per mole.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is essential for converting between the mass of a substance and the number of moles. In this problem, knowing the molar mass of Fe2O3 allows us to calculate how many grams are required to produce a specific amount of heat, linking the energy produced to the physical quantity of the reactant.

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Molar Mass Concept

Related Practice

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 → 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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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 theUgi reaction:R1C(=O)R2 + R3 - NH2 + R4COOH + R5NC SR4C(=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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