Which one of the following equations is the balanced chemical equation for the given reaction? Fe + H2O → Fe3O4 + H2
3Fe + 4H 2 O→ Fe 3 O 4 + 4H 2
Understanding Balanced Chemical Equations
A balanced chemical equation represents a chemical reaction where the number of atoms of each element is the same on both the reactant side (left side) and the product side (right side). This follows the law of conservation of mass, which states that mass cannot be created or destroyed in a chemical reaction. Balancing ensures that the total mass of the reactants equals the total mass of the products.
The Given Unbalanced Reaction
The reaction provided is between iron (Fe) and water (H2O) to produce iron(II,III) oxide (Fe3O4) and hydrogen gas (H2):
\(\text{Fe} + \text{H}_2\text{O} \rightarrow \text{Fe}_3\text{O}_4 + \text{H}_2\)
This equation is unbalanced because the number of atoms of each element is not equal on both sides.
Steps to Balance the Chemical Equation
To balance the chemical equation, we adjust the coefficients (the numbers placed in front of the chemical formulas) until the number of atoms of each element is equal on both sides. We cannot change the subscripts in the chemical formulas.
Let's count the atoms in the unbalanced equation:
| Element | Number of atoms in Reactants (\(\text{Fe} + \text{H}_2\text{O}\)) | Number of atoms in Products (\(\text{Fe}_3\text{O}_4 + \text{H}_2\)) |
|---|---|---|
| Fe | 1 | 3 |
| H | 2 | 2 |
| O | 1 | 4 |
We can see that the number of Fe and O atoms is not balanced.
Let's balance the atoms following a common strategy, such as balancing metals first, then non-metals (excluding H and O), then O, and finally H. Or, pick the molecule with the most atoms or elements to start.
- The molecule \(\text{Fe}_3\text{O}_4\) has the most atoms. It has 3 Fe atoms and 4 O atoms.
- Balance Fe atoms: There are 3 Fe atoms in \(\text{Fe}_3\text{O}_4\) on the product side, but only 1 Fe atom in the reactants. To balance Fe, place a coefficient of 3 in front of Fe in the reactants: \(\text{3Fe} + \text{H}_2\text{O} \rightarrow \text{Fe}_3\text{O}_4 + \text{H}_2\) Now the counts are: Reactants (3 Fe, 2 H, 1 O), Products (3 Fe, 2 H, 4 O). Fe is balanced.
- Balance O atoms: There are 4 O atoms in \(\text{Fe}_3\text{O}_4\) on the product side, but only 1 O atom in \(\text{H}_2\text{O}\) in the reactants. To balance O, place a coefficient of 4 in front of \(\text{H}_2\text{O}\) in the reactants: \(\text{3Fe} + \text{4H}_2\text{O} \rightarrow \text{Fe}_3\text{O}_4 + \text{H}_2\) Now the counts are: Reactants (3 Fe, \(4 \times 2 = 8\) H, \(4 \times 1 = 4\) O), Products (3 Fe, 2 H, 4 O). Fe and O are balanced.
- Balance H atoms: Now, hydrogen is unbalanced. There are 8 H atoms in the reactants (\(4 \times \text{H}_2\text{O}\)) and only 2 H atoms in \(\text{H}_2\) in the products. To balance H, place a coefficient of 4 in front of \(\text{H}_2\) in the products: \(\text{3Fe} + \text{4H}_2\text{O} \rightarrow \text{Fe}_3\text{O}_4 + \text{4H}_2\)
Verifying the Balanced Equation
Let's count the atoms on both sides of the proposed balanced equation: \(3\text{Fe} + 4\text{H}_2\text{O} \rightarrow \text{Fe}_3\text{O}_4 + 4\text{H}_2\)
| Element | Number of atoms in Reactants (\(3\text{Fe} + 4\text{H}_2\text{O}\)) | Number of atoms in Products (\(\text{Fe}_3\text{O}_4 + 4\text{H}_2\)) |
|---|---|---|
| Fe | \(3 \times 1 = 3\) | 3 |
| H | \(4 \times 2 = 8\) | \(4 \times 2 = 8\) |
| O | \(4 \times 1 = 4\) | 4 |
The number of atoms for each element is equal on both sides of the equation. Therefore, the equation is balanced.
The balanced chemical equation is: \(3\text{Fe} + 4\text{H}_2\text{O} \rightarrow \text{Fe}_3\text{O}_4 + 4\text{H}_2\).
Checking Other Options
- Option 1: \(\text{Fe} + 4\text{H}_2\text{O} \rightarrow \text{Fe}_3\text{O}_4 + \text{H}_2\) (Fe: 1 vs 3, O: 4 vs 4, H: 8 vs 2) - Unbalanced.
- Option 2: \(3\text{Fe} + \text{H}_2\text{O} \rightarrow \text{Fe}_3\text{O}_4 + 2\text{H}_2\) (Fe: 3 vs 3, O: 1 vs 4, H: 2 vs 4) - Unbalanced.
- Option 4: \(3\text{Fe} + 4\text{H}_2\text{O} \rightarrow \text{Fe}_3\text{O}_4 + \text{H}_2\) (Fe: 3 vs 3, O: 4 vs 4, H: 8 vs 2) - Unbalanced.
Only the equation \(3\text{Fe} + 4\text{H}_2\text{O} \rightarrow \text{Fe}_3\text{O}_4 + 4\text{H}_2\) correctly shows the same number of atoms of each element on both sides.
Revision Table: Key Concepts in Balancing Equations
| Concept | Description |
|---|---|
| Law of Conservation of Mass | Total mass of reactants equals total mass of products. Atoms are rearranged, not created or destroyed. |
| Reactants | Substances that start a chemical reaction (left side of the arrow). |
| Products | Substances that are formed in a chemical reaction (right side of the arrow). |
| Coefficients | Numbers placed in front of chemical formulas to balance the equation. They multiply the number of atoms of each element in the formula. |
| Subscripts | Numbers written below and to the right of an element symbol in a chemical formula. They indicate the number of atoms of that element in one molecule. Subscripts must never be changed when balancing. |
Additional Information: Significance of Balancing
Balancing chemical equations is crucial for several reasons in chemistry:
- Stoichiometry: Balanced equations provide the mole ratios between reactants and products. These ratios are used to calculate the amounts of substances consumed or produced in a reaction.
- Predicting Yields: Knowing the balanced equation allows chemists to predict the theoretical yield of a product based on the amount of starting material.
- Understanding Reaction Mechanisms: While a balanced equation shows the overall change, understanding how atoms rearrange helps in studying reaction mechanisms.
- Safety and Efficiency: In industrial processes, precise amounts of reactants are needed for efficient and safe production, guided by balanced equations.
The reaction between iron and steam (high-temperature water) to produce iron(II,III) oxide and hydrogen gas is a significant one, especially in the history of materials science and in certain types of hydrogen production processes.
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