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Ch.7 Chemical Reactions: Energy, Rate and Equilibrium
McMurry - Fundamentals of General, Organic, and Biological Chemistry 8th Edition
McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoMcMurry 8th EditionCh.7 Chemical Reactions: Energy, Rate and EquilibriumProblema 74c
Capitolo 7, Problema 74c

Methanol, CH3OH, is used as race car fuel.
c. How many kilojoules are released by burning 50.0 g of methanol?

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1
Determine the balanced chemical equation for the combustion of methanol. The reaction is: CH3OHl+3⁢O2g→2H2Og+2CO2g. This equation shows that methanol reacts with oxygen to produce water and carbon dioxide.
Find the molar mass of methanol, CH3OH. Add the atomic masses of its elements: Carbon (C) = 12.01 g/mol, Hydrogen (H) = 1.008 g/mol (×4), and Oxygen (O) = 16.00 g/mol. The molar mass is: 12.01+(4⁢1.008)+16.00 g/mol.
Convert the given mass of methanol (50.0 g) to moles using the formula: n=mM, where m is the mass (50.0 g) and M is the molar mass of methanol.
Determine the energy released per mole of methanol burned. This value is typically provided in the problem or can be found in a reference table. For example, the combustion of methanol releases approximately 726⁢kJ per mole.
Calculate the total energy released by multiplying the moles of methanol (from step 3) by the energy released per mole (from step 4). Use the formula: E=n⁢∆H, where E is the total energy, n is the number of moles, and ∆H is the energy released per mole.

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Combustion Reaction

A combustion reaction is a chemical process in which a substance reacts rapidly with oxygen, releasing energy in the form of heat and light. In the case of methanol (CH3OH), its combustion produces carbon dioxide (CO2) and water (H2O), along with a significant amount of energy. Understanding this reaction is crucial for calculating the energy released when burning a specific mass of methanol.
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Common Types of Alkane Reactions Concept 1

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). For methanol, the molar mass is approximately 32.04 g/mol. Knowing the molar mass allows us to convert grams of methanol into moles, which is essential for determining the amount of energy released during combustion based on stoichiometric calculations.
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Calculating Molar Mass

Heat of Combustion

The heat of combustion is the amount of energy released when one mole of a substance is completely burned in oxygen. For methanol, the heat of combustion is about -726 kJ/mol. This value is critical for calculating the total energy released when a specific mass of methanol is combusted, as it provides a direct relationship between the amount of fuel and the energy produced.
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Heat Capacity
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Sketch an energy diagram for a system in which the forward reaction has Eact = +25 kcal/mol (+105 kJ/mol) and the reverse reaction has Eact = +35 kcal/mol (+146 kJ/mol).

a. Is the forward process endergonic or exergonic?

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For the evaporation of water, H2O(l) → H2O(g), at 100°C, ∆H = +9.72 kcal/mol (+40.7 kJ/mol).

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