Question

In which chemical equation is the number of atoms in the reactants the same as the number of atoms in the products?
1. Li2CO3 → LiO + CO2
2. Zn + 2HCl → H2 + ZnCl2
3. CH4 + O2 → CO2 + 2H2O
4. CO2 + H2O → CH2OH + O2

Answer 1

To determine which chemical equation has the same number of atoms in the reactants as in the products, we should count the number of atoms for each element in the reactants and products of each equation.

1. **Li2CO3 → LiO + CO2**
- Reactants: 2 Li, 1 C, 3 O (total: 6 atoms)
- Products: 1 Li, 1 C, 2 O + 1 Li, 2 O (total: 4 atoms; Li: 1, C: 1, O: 4)
- (6 vs. 4) Not balanced.

2. **Zn + 2HCl → H2 + ZnCl2**
- Reactants: 1 Zn, 2 H, 2 Cl (total: 5 atoms)
- Products: 1 H, 2 Cl + 2 H (total: 4 atoms; Zn: 1, H: 2, Cl: 2)
- (5 vs. 4) Not balanced.

3. **CH4 + O2 → CO2 + 2H2O**
- Reactants: 1 C, 4 H, 2 O (total: 7 atoms)
- Products: 1 C + 2 O (from CO2), 2 H, 1 O (from 2 H2O) (total: 7 atoms; C: 1, H: 4, O: 3)
- (7 vs. 7) Balanced.

4. **CO2 + H2O → CH2OH + O2**
- Reactants: 1 C, 2 O (from CO2), 2 H, 1 O (from H2O) (total: 5 atoms)
- Products: 1 C, 2 H, 1 O (from CH2OH), 2 O (from O2) (total: 5 atoms; C: 1, H: 2, O: 3)
- (5 vs. 5) Not balanced.

Upon reviewing the calculations, the third equation (CH4 + O2 → CO2 + 2H2O) has the same number of atoms in the reactants as in the products.

**Final answer: 3. CH4 + O2 → CO2 + 2H2O**