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Ch.21 - Organic Chemistry
Chapter 21, Problem 95

What is the minimum amount of hydrogen gas, in grams, required to completely hydrogenate 15.5 kg of 2-butene?

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1
Identify the chemical reaction involved: The hydrogenation of 2-butene (C4H8) involves adding hydrogen (H2) to convert it into butane (C4H10). The balanced chemical equation is: C4H8 + H2 -> C4H10.
Calculate the molar mass of 2-butene (C4H8) and hydrogen gas (H2). Use the atomic masses: C = 12.01 g/mol and H = 1.008 g/mol.
Determine the number of moles of 2-butene in 15.5 kg. Convert the mass from kilograms to grams, then use the molar mass of 2-butene to find the moles.
Use the stoichiometry of the balanced equation to find the moles of hydrogen gas needed. According to the equation, 1 mole of C4H8 reacts with 1 mole of H2.
Convert the moles of hydrogen gas to grams using the molar mass of H2. This will give you the minimum amount of hydrogen gas required.

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 chemists to calculate the amounts of substances consumed and produced in a reaction based on balanced chemical equations. Understanding stoichiometry is essential for determining how much hydrogen gas is needed to react with a given amount of 2-butene.
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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 crucial for converting between the mass of a substance and the number of moles, which is necessary for stoichiometric calculations. For this question, knowing the molar mass of hydrogen gas (H2) and 2-butene (C4H8) will enable the calculation of the required mass of hydrogen for complete hydrogenation.
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Hydrogenation Reaction

Hydrogenation is a chemical reaction that involves the addition of hydrogen (H2) to an unsaturated compound, such as alkenes or alkynes, converting them into saturated compounds. In the case of 2-butene, hydrogenation will convert it into butane. Understanding the nature of this reaction helps in determining the stoichiometric coefficients needed to calculate the amount of hydrogen required for the complete reaction.
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