When iron metal reacts with sulfuric acid, it produces iron (III) sulfate and hydrogen gas.

Question

Balance the equation: Fe + H2SO4 → Fe2(SO4)3 + H2
Describe why it is necessary to balance chemical equations.
Explain why coefficients can be included to and changed in a chemical equation, but subscripts cannot be changed.

Answer 1

Balancing the Equation

To balance the chemical equation for the reaction of iron (Fe) with sulfuric acid (H₂SO₄) to produce iron(III) sulfate (Fe₂(SO₄)₃) and hydrogen gas (H₂), we start with the unbalanced equation:

\[ \text{Fe} + \text{H}_2\text{SO}_4 \rightarrow \text{Fe}_2(\text{SO}_4)_3 + \text{H}_2 \]

1. Count the atoms for each element on both sides of the equation:

   • Left:
     • Fe: 1
     • H: 2
     • S: 1
     • O: 4
   • Right:
     • Fe: 2
     • H: 2
     • S: 3
     • O: 12

2. Balance the iron (Fe) by placing a coefficient of 2 before Fe on the left side:

   \[ 2\text{Fe} + \text{H}_2\text{SO}_4 \rightarrow \text{Fe}_2(\text{SO}_4)_3 + \text{H}_2 \]

3. Now we have:

   • Left:
     • Fe: 2
     • H: 2
     • S: 1
     • O: 4
   • Right:
     • Fe: 2
     • H: 2
     • S: 3
     • O: 12

4. To balance sulfur (S), add a coefficient of 3 before H₂SO₄:

   \[ 2\text{Fe} + 3\text{H}_2\text{SO}_4 \rightarrow \text{Fe}_2(\text{SO}_4)_3 + 3\text{H}_2 \]

5. Check the atom balance again:

   • Left:
     • Fe: 2
     • H: 6
     • S: 3
     • O: 12
   • Right:
     • Fe: 2
     • H: 6
     • S: 3
     • O: 12

Now, the equation is balanced:

\[ 2\text{Fe} + 3\text{H}_2\text{SO}_4 \rightarrow \text{Fe}_2(\text{SO}_4)_3 + 3\text{H}_2 \]

Importance of Balancing Chemical Equations

Why it is necessary to balance chemical equations: Balancing chemical equations is crucial because it reflects the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. Balancing ensures that the same number of each type of atom is present on both the reactant and product sides of the equation, indicating that all reactants and products are accounted for and that the reaction is accurate from a stoichiometric perspective.

Coefficients vs. Subscripts

Why coefficients can be changed, but subscripts cannot:

• Coefficients are numbers placed before compounds in a chemical equation to indicate the number of molecules or moles of that compound participating in the reaction. Adjusting coefficients allows chemists to satisfy the requirement of balancing atoms across the equation while still representing the same molecular formulas.

• Subscripts, on the other hand, indicate the actual number of atoms present within a single molecule of a compound. Changing a subscript alters the chemical identity of the substance; for example, changing H₂O (water) to H₂O₂ changes it to hydrogen peroxide, which has entirely different properties. Therefore, subscripts must remain constant to accurately represent the actual molecules involved in the reaction.