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Ch.3 - Mass Relationships in Chemical Reactions
Chapter 3, Problem 2

What are the coefficients in the balanced equation for the combustion of ethanol? (LO 3.2) (a) 1, 3, 2, 3 (b) 2, 3, 4, 3 (c) 2, 7, 4, 6 (d) 1, 4, 2, 3

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1
Identify the chemical formula for ethanol, which is \( \text{C}_2\text{H}_5\text{OH} \).
Write the unbalanced chemical equation for the combustion of ethanol: \( \text{C}_2\text{H}_5\text{OH} + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} \).
Balance the carbon atoms: There are 2 carbon atoms in ethanol, so place a coefficient of 2 in front of \( \text{CO}_2 \).
Balance the hydrogen atoms: There are 6 hydrogen atoms in ethanol, so place a coefficient of 3 in front of \( \text{H}_2\text{O} \).
Balance the oxygen atoms: Count the total oxygen atoms needed on the right side and adjust the coefficient of \( \text{O}_2 \) accordingly.

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Key Concepts

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

Combustion Reaction

A combustion reaction is a chemical process in which a substance (usually a hydrocarbon) reacts with oxygen to produce carbon dioxide and water, releasing energy in the form of heat and light. In the case of ethanol (C2H5OH), the balanced equation must account for the complete combustion of the molecule, ensuring that all atoms are conserved in the products.
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Balancing Chemical Equations

Balancing chemical equations involves adjusting the coefficients of reactants and products to ensure that the number of atoms of each element is the same on both sides of the equation. This is crucial for obeying the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. The coefficients represent the relative amounts of each substance involved.
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Stoichiometry

Stoichiometry is the quantitative relationship between the amounts of reactants and products in a chemical reaction. It allows chemists to predict how much of each substance is consumed or produced based on the balanced equation. Understanding stoichiometry is essential for determining the correct coefficients in a balanced equation, such as that for the combustion of ethanol.
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