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Ch.4 - Chemical Quantities & Aqueous Reactions
Chapter 4, Problem 27

Calculate how many moles of NO2 form when each quantity of reactant completely reacts. Reaction: 2 N2O5(g) → 4 NO2(g) + O2(g) a. 15.2 g N2O5 b. 6.8 mol N2O5 c. 2.87 kg N2O5

Verified step by step guidance
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Step 1: Identify the balanced chemical equation. The reaction given is 2 N2O5(g) → 4 NO2(g) + O2(g). This tells us that 2 moles of N2O5 produce 4 moles of NO2.
Step 2: For part (a), convert the mass of N2O5 to moles. Use the molar mass of N2O5, which is approximately 108.01 g/mol. Calculate the moles of N2O5 by dividing the given mass (15.2 g) by the molar mass.
Step 3: Use the stoichiometry of the reaction to find the moles of NO2 produced. From the balanced equation, 2 moles of N2O5 produce 4 moles of NO2. Use this ratio to convert moles of N2O5 to moles of NO2.
Step 4: For part (b), directly use the given moles of N2O5 (6.8 mol) and apply the stoichiometric ratio from the balanced equation to find the moles of NO2.
Step 5: For part (c), convert the mass of N2O5 from kilograms to grams (2.87 kg = 2870 g). Then, follow the same process as in Step 2 to convert grams to moles, and use the stoichiometric ratio to find the moles of NO2.

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 reactants and products in a chemical reaction. It allows us to calculate the amount of substances consumed and produced in a reaction based on balanced chemical equations. In this case, the stoichiometric coefficients from the balanced equation (2 N2O5 → 4 NO2 + O2) indicate that 2 moles of N2O5 produce 4 moles of NO2, establishing a direct ratio for calculations.
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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 grams and moles, allowing us to determine how many moles of a substance are present in a given mass. For N2O5, the molar mass can be calculated by summing the atomic masses of nitrogen and oxygen, which is necessary for the calculations in parts a and c of the question.
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Conversion Factors

Conversion factors are ratios that express how one unit relates to another, facilitating the conversion between different units of measurement. In this context, conversion factors are used to convert grams of N2O5 to moles using its molar mass, and to convert kilograms to grams. Understanding how to apply these factors is crucial for accurately determining the number of moles of NO2 produced from the given quantities of N2O5.
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