Ch.3 - Chemical Reactions and Reaction Stoichiometry

Problem 73a

Chapter 3, Problem 73a

(a) Define the terms limiting reactant and excess reactant.

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The limiting reactant in a chemical reaction is the substance that is completely consumed first, limiting the amount of product that can be formed. It determines the maximum amount of product that can be produced in the reaction.

To identify the limiting reactant, compare the mole ratio of the reactants used in the reaction to the mole ratio in the balanced chemical equation.

The excess reactant is the substance that remains after the reaction has gone to completion. It is present in a greater amount than necessary to completely react with the limiting reactant.

To find the excess reactant, calculate how much of it is left over after the reaction by subtracting the amount that reacted from the initial amount.

Understanding these concepts is crucial for stoichiometry calculations, as they help predict the quantities of products formed and reactants consumed in a chemical reaction.

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Key Concepts

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

Limiting Reactant

The limiting reactant is the substance in a chemical reaction that is completely consumed first, thus determining the maximum amount of product that can be formed. It limits the extent of the reaction because once it is used up, the reaction cannot proceed further, regardless of the amounts of other reactants present.

Excess Reactant

The excess reactant is the substance that remains after the reaction has gone to completion. It is present in a greater quantity than necessary to react with the limiting reactant. Understanding which reactant is in excess helps in calculating the efficiency of the reaction and the amount of leftover material.

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It involves using balanced chemical equations to calculate the amounts of substances consumed and produced, which is essential for identifying limiting and excess reactants.

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Textbook Question

Detonation of nitroglycerin proceeds as follows: 4 C3H5N3O91l2¡ 12 CO21g2 + 6 N21g2 + O21g2 + 10 H2O1g2 (a) If a sample containing 2.00 mL of nitroglycerin 1density = 1.592 g>mL2 is detonated, how many moles of gas are produced?

The combustion of one mole of liquid octane, CH3(CH2)6CH3, produces 5470 kJ of heat. Calculate how much heat is produced if 1.000 gallon of octane is combusted.

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Textbook Question

(b) Why are the amounts of products formed in a reaction determined only by the amount of the limiting reactant?

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Textbook Question

(c) Why should you base your choice of which compound is the limiting reactant on its number of initial moles, not on its initial mass in grams?

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Textbook Question

(a) Define the terms theoretical yield, actual yield, and percent yield.

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