To balance the chemical equation for the combustion of heptane (C7H16), we first need to determine the number of atoms involved in the reactants and products.
The unbalanced equation is:
\[ C_7H_{16} + O_2 \rightarrow CO_2 + H_2O \]
Counting Atoms
- Reactants:
- In C7H16:
- Carbon (C): 7
- Hydrogen (H): 16
- In O2:
- Oxygen (O): 2 (but we will balance this later)
- In C7H16:
Total initial atoms in reactants:
- C: 7
- H: 16
- O: (to be determined)
This gives us a total of 7 + 16 + 2 = 25 atoms (including O2 before balancing).
- Products:
- Each CO2 contains:
- Carbon (C): 1
- Oxygen (O): 2
- Each H2O contains:
- Hydrogen (H): 2
- Oxygen (O): 1
- Each CO2 contains:
Balancing the Equation
To balance the combustion reaction:
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Since there are 7 carbons in the reactant, we need 7 CO2:
\[ C_7H_{16} + O_2 \rightarrow 7 CO_2 + H_2O \]
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Since there are 16 hydrogens in the reactant, we need 8 H2O (because 2 H in each H2O):
\[ C_7H_{16} + O_2 \rightarrow 7 CO_2 + 8 H_2O \]
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Now count the oxygen in the products:
- From 7 CO2: 7 * 2 = 14 O
- From 8 H2O: 8 * 1 = 8 O
- Total oxygen needed: 14 + 8 = 22 O
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Since each O2 molecule has 2 O: \[ \frac{22}{2} = 11 \text{ O2} \]
The balanced equation is:
\[ C_7H_{16} + 11 O_2 \rightarrow 7 CO_2 + 8 H_2O \]
Total Atom Count
Now, re-count the total number of atoms in the balanced equation:
- Reactants:
- C: 7
- H: 16
- O: 22 (from 11 O2)
Total in reactants: 7 + 16 + 22 = 45 atoms
- Products:
- C: 7 (from 7 CO2)
- H: 16 (from 8 H2O)
- O: 22 (14 from 7 CO2 and 8 from 8 H2O)
Total in products: 7 + 16 + 22 = 45 atoms
Conclusion
The question, however, asked about the total number of atoms in the unbalanced equation. Before balancing, we counted 25 atoms.
Therefore, for your specific response options, if they refer to the total in the unbalanced state, the correct answer is 25 atoms.
Please confirm if you need clarification or a different part of this reaction!