Chapter 5: Problem 69
Methanol, ethanol, and
Short Answer
Expert verified
The heats of combustion are: methanol -724 kJ/mol, ethanol -1370 kJ/mol, n-propanol -2010 kJ/mol.
Step by step solution
01
Determine Molar Mass of Methanol
The molecular formula of methanol is . To find the molar mass, add the atomic masses of each element: .
02
Calculate Heat of Combustion for Methanol
Given that 1.00 g of methanol releases , convert this to per mole using the molar mass: .
03
Determine Molar Mass of Ethanol
The molecular formula of ethanol is . Calculate the molar mass: .
04
Calculate Heat of Combustion for Ethanol
Given that 1.00 g of ethanol releases , convert this to per mole using the molar mass: .
05
Determine Molar Mass of n-Propanol
The molecular formula of -propanol is . Calculate the molar mass: .
06
Calculate Heat of Combustion for n-Propanol
Given that 1.00 g of -propanol releases , convert this to per mole using the molar mass: .
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Molar Mass
The molar mass is a crucial concept in chemistry that helps us understand how much one mole of a given substance weighs. It is expressed in grams per mole ( ). To calculate the molar mass, you add the atomic masses of all the atoms in a molecule. This is particularly important when working with heat of combustion as it allows us to convert energy values from per gram to per mole.
This conversion shows more accurately how much energy is released when a full mole of a substance undergoes combustion. Knowing the molar mass makes it easier to measure and predict outcomes in chemical reactions.
This conversion shows more accurately how much energy is released when a full mole of a substance undergoes combustion. Knowing the molar mass makes it easier to measure and predict outcomes in chemical reactions.
Alcohols
Alcohols are a group of organic compounds characterized by the presence of one or more hydroxyl ( ) groups attached to a carbon atom. They are widely used in various applications, from industrial solvents to alcoholic beverages.
- Methanol (
) is often used as a solvent and fuel. - Ethanol (
) is commonly found in alcoholic drinks. - n-Propanol (
) is used in pharmaceuticals and cosmetics.
Enthalpy Change
Enthalpy change, denoted as , is a measure of the total heat content in a chemical reaction. It's an important thermodynamic property that reflects the heat absorbed or released at constant pressure. For combustion reactions, the heat of combustion is the enthalpy change when one mole of a substance is burned completely in oxygen. It's usually a negative value, signifying that the process releases energy to the surroundings, i.e., it is exothermic.
Enthalpy changes help gauge reaction favorability and feasibility in industrial processes.
Enthalpy changes help gauge reaction favorability and feasibility in industrial processes.
Methanol
Methanol, with the chemical formula , is the simplest alcohol. It has a molar mass of 32.04 g/mol and is a light, volatile, colorless, flammable liquid with a distinctive alcohol-like odor. Methanol is used in the production of formaldehyde and acetic acid. Being toxic, it must be handled with care.
In combustion, methanol releases , highlighting its potential use as a fuel source.
In combustion, methanol releases
Ethanol
Ethanol ( ) is a common alcohol with numerous uses, including in beverages, as a fuel additive, and as a biomedical solvent. It has a molar mass of 46.08 g/mol.
Ethanol's heat of combustion is . This value shows the energy potential when ethanol completely burns, which is why it is often considered as a biofuel. Its energy release makes it a potential candidate for blending with gasoline.
Ethanol's heat of combustion is
n-Propanol
n-Propanol, or 1-propanol ( ), is an alcohol that finds its applications in the manufacturing of cosmetics and antiseptics. With a molar mass of 60.10 g/mol, this primary alcohol is also used as a solvent and intermediate in chemical synthesis.
The exothermic combustion of n-propanol results in a heat release of , making it more energy-dense than methanol and ethanol.
The exothermic combustion of n-propanol results in a heat release of
Chemical Reactions
Chemical reactions involve the transformation of substances in which reactants are converted into products. They obey the law of conservation of mass, meaning the mass of the products in a chemical reaction must equal the mass of the reactants.
In the context of combustion, alcohols react with oxygen to produce carbon dioxide and water, releasing energy. The balanced chemical equations help predict the stoichiometry of the reaction and the amount of energy transferred.
In the context of combustion, alcohols react with oxygen to produce carbon dioxide and water, releasing energy. The balanced chemical equations help predict the stoichiometry of the reaction and the amount of energy transferred.