Chapter 4: Problem 15
Complete and balance each combustion equation. a) \(\mathrm{C}_{4} \mathrm{H}_{9} \mathrm{OH}+\mathrm{O}_{2} \rightarrow\) ? b) \(\mathrm{CH}_{3} \mathrm{NO}_{2}+\mathrm{O}_{2} \rightarrow ?\)
Short Answer
Expert verified
a) \( 2\mathrm{C}_4 \mathrm{H}_9 \mathrm{OH} + 13\mathrm{O}_2 \rightarrow 8\mathrm{CO}_2 + 10\mathrm{H}_2O \).
b) \( 2\mathrm{CH}_3 \mathrm{NO}_2 + 3\mathrm{O}_2 \rightarrow 2\mathrm{CO}_2 + 3\mathrm{H}_2O + \mathrm{N}_2 \).
Step by step solution
01
Understand Combustion Reaction
Combustion reactions involve a hydrocarbon (or related compound) reacting with oxygen to produce carbon dioxide and water. The general formula for a combustion reaction is: \[ \text{Hydrocarbon} + O_2 \rightarrow CO_2 + H_2O \]
02
Write Unbalanced Equation for A
For the compound \( \mathrm{C}_4 \mathrm{H}_9 \mathrm{OH} \), which is butanol, we write the unbalanced equation: \[ \mathrm{C}_4 \mathrm{H}_9 \mathrm{OH} + \mathrm{O}_2 \rightarrow \mathrm{CO}_2 + \mathrm{H}_2O \]
03
Balance Equation for A
To balance the equation, start by balancing the carbon atoms. There are 4 carbon atoms in \( \mathrm{C}_4 \mathrm{H}_9 \mathrm{OH} \), so we need 4 \( \mathrm{CO}_2 \): \[ \mathrm{C}_4 \mathrm{H}_9 \mathrm{OH} + \mathrm{O}_2 \rightarrow 4\mathrm{CO}_2 + \mathrm{H}_2O \] Next, balance the hydrogen atoms. There are 10 hydrogen atoms in \( \mathrm{C}_4 \mathrm{H}_9 \mathrm{OH} \), so we need 5 \( \mathrm{H}_2O \): \[ \mathrm{C}_4 \mathrm{H}_9 \mathrm{OH} + \mathrm{O}_2 \rightarrow 4\mathrm{CO}_2 + 5\mathrm{H}_2O \] Now, balance the oxygen atoms. There are a total of 13 oxygen atoms needed (8 from \( 4 \mathrm{CO}_2 \) and 5 from \( 5 \mathrm{H}_2O \)), and since \( \mathrm{O}_2 \) is a diatomic molecule, we need \( 13/2 \) or 6.5 \( \mathrm{O}_2 \). To avoid fractions, multiply the entire equation by 2: \[ 2\mathrm{C}_4 \mathrm{H}_9 \mathrm{OH} + 13\mathrm{O}_2 \rightarrow 8\mathrm{CO}_2 + 10\mathrm{H}_2O \]
04
Write Unbalanced Equation for B
For the compound \( \mathrm{CH}_3 \mathrm{NO}_2 \), we write the unbalanced equation: \[ \mathrm{CH}_3 \mathrm{NO}_2 + \mathrm{O}_2 \rightarrow \mathrm{CO}_2 + \mathrm{H}_2O + \mathrm{N}_2 \] Note: In combustion, nitrogen usually forms \( \mathrm{N}_2 \) gas.
05
Balance Equation for B
To balance the equation, start by balancing the carbon atoms. There is 1 carbon atom in \( \mathrm{CH}_3 \mathrm{NO}_2 \), so we keep 1 \( \mathrm{CO}_2 \): \[ \mathrm{CH}_3 \mathrm{NO}_2 + \mathrm{O}_2 \rightarrow \mathrm{CO}_2 + \mathrm{H}_2O + \mathrm{N}_2 \] Next, balance the hydrogen atoms. There are 3 hydrogen atoms in \( \mathrm{CH}_3 \mathrm{NO}_2 \), so we need \( 1.5 \mathrm{H}_2O \). To avoid fractions initially: \[ 2\mathrm{CH}_3 \mathrm{NO}_2 + \mathrm{O}_2 \rightarrow 2\mathrm{CO}_2 + 3\mathrm{H}_2O + \mathrm{N}_2 \] Now, balance nitrogen. There are 2 nitrogen atoms in 2 molecules of \( \mathrm{CH}_3 \mathrm{NO}_2 \), so we have \( \mathrm{N}_2 \): \[ 2\mathrm{CH}_3 \mathrm{NO}_2 + \mathrm{O}_2 \rightarrow 2\mathrm{CO}_2 + 3\mathrm{H}_2O + \mathrm{N}_2 \] Finally, balance the oxygen atoms. We need 7 oxygen atoms (4 from 2 \( \mathrm{CO}_2 \), 3 from 3 \( \mathrm{H}_2O \)). Since each \( \mathrm{CH}_3 \mathrm{NO}_2 \) contributes 2 oxygen atoms, we need 3 more from \( \mathrm{O}_2 \), or 1.5 \( \mathrm{O}_2 \) per molecule of \( \mathrm{CH}_3 \mathrm{NO}_2 \), leading to: \[ 3\mathrm{O}_2 \] Thus, the balanced equation is: \[ 2\mathrm{CH}_3 \mathrm{NO}_2 + 3\mathrm{O}_2 \rightarrow 2\mathrm{CO}_2 + 3\mathrm{H}_2O + \mathrm{N}_2 \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Chemical Equation Balancing
Balancing chemical equations is a fundamental skill in chemistry. It ensures that the law of conservation of mass is obeyed—meaning matter is neither created nor destroyed in a reaction. Every chemical equation represents a reaction, and balancing ensures that the number of each type of atom on the reactant side equals the number on the product side. Here's how it works:
- Identify each type of atom present in the reactants and products.
- Count how many atoms of each type you have on both sides.
- Add coefficients (whole numbers placed before compounds) to ensure equal numbers of each atom on both sides.
- Check your work by recounting atoms to confirm balance.
Hydrocarbon Combustion
Hydrocarbon combustion is a specific type of chemical reaction where a hydrocarbon reacts with oxygen gas to produce carbon dioxide and water. These reactions are a vital part of energy production, as seen in engines and power plants. The basic form for any combustion of hydrocarbon can be generalized as:
\[ \text{Hydrocarbon} + O_2 \rightarrow CO_2 + H_2O \]
Key points to understand this reaction include:
\[ \text{Hydrocarbon} + O_2 \rightarrow CO_2 + H_2O \]
Key points to understand this reaction include:
- "Hydrocarbons" consist mainly of carbon (C) and hydrogen (H), often accompanied by other elements like oxygen in alcohols (e.g., butanol).
- The reaction with O\(_2\) is highly exothermic, meaning it releases energy, often in the form of heat and light.
- For a complete combustion, enough oxygen must be present to ensure that the hydrocarbons are entirely converted into CO\(_2\) and water.
Stoichiometry
Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. When a chemical equation is balanced, stoichiometry allows us to use the coefficients to determine proportions. This means we can calculate precisely how much of each reactant is needed to produce a desired amount of product. Here's how to apply it:
- Use the balanced equation to determine the mole ratio between reactants and products.
- Convert masses or volumes of substances into moles, using their molecular weights.
- Apply the mole ratios to calculate unknown quantities, whether it's amount of a reactant needed or the amount of product formed.