To determine which of the chemical equations has the same number of atoms in the reactants as in the products, we'll need to balance each equation.
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CH₄ + 2 O₂ → CO₂ + 2 H₂O
- Reactants: 1 C (from CH₄) + 4 H (from CH₄) + 4 O (from 2 O₂) = 1 C + 4 H + 4 O
- Products: 1 C (from CO₂) + 4 H (from 2 H₂O) + 2 O (from CO₂ and 2 H₂O) = 1 C + 4 H + 4 O
- This equation is balanced—same number of atoms in reactants and products.
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Li₂CO₃ → Li₂O + CO₂
- Reactants: 2 Li + 1 C + 3 O = 2 Li + 1 C + 3 O
- Products: 2 Li + 1 O + 1 C + 2 O = 2 Li + 1 C + 3 O
- This equation is also balanced.
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Zn + 2 HCl → H₂ + ZnCl₂
- Reactants: 1 Zn + 2 H + 2 Cl = 1 Zn + 2 H + 2 Cl
- Products: 1 H + 1 H + 1 Zn + 2 Cl = 1 Zn + 2 H + 2 Cl
- This equation is balanced.
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CO₂ + H₂O → CH₂O + O₂
- Reactants: 1 C + 2 O + 2 H = 1 C + 2 O + 2 H
- Products: 1 C + 2 H + 1 O + 2 O = 1 C + 2 H + 3 O
- This equation is not balanced—there's an extra O in the products.
Based on the analysis above:
- The first equation (CH₄ + 2 O₂ → CO₂ + 2 H₂O) is balanced.
- The second equation (Li₂CO₃ → Li₂O + CO₂) is balanced.
- The third equation (Zn + 2 HCl → H₂ + ZnCl₂) is balanced.
- The fourth equation (CO₂ + H₂O → CH₂O + O₂) is not balanced.
Therefore, the first three reactions have the same number of atoms in the reactants as in the products.