Chapter 1 · Question 5
Balance the following equation using the hit-and-trial method and write the final balanced equation with state symbols: . Why is H₂O written with the state symbol (g) in the balanced form?
Q5
Balance the following equation using the hit-and-trial method and write the final balanced equation with state symbols: . Why is H₂O written with the state symbol (g) in the balanced form?
Answer Revealed
Direct Answer:
Using the hit-and-trial method: Initial skeletal equation . Step I — balance oxygen: add coefficient 4 to H₂O → . Step II — balance hydrogen: add coefficient 4 to H₂ → . Step III — balance iron: add coefficient 3 to Fe → . Final balanced equation with state symbols: . H₂O is written as (g) because steam (water vapour) is used in this reaction.
Simple Explanation
Walk through the balancing step by step: Start with . There are 4 O on right vs 1 on left, so put 4 before H₂O. Now hydrogen has 8 atoms on left vs 2 on right, so put 4 before H₂. Now Fe is 1 on left vs 3 on right, so put 3 before Fe. The balanced equation: . The state symbols are (s) for solid metals and (g) for gases — the water is steam (g) in this reaction.
Exam-Ready Structure
The systematic step-by-step balancing of illustrates the hit-and-trial method: 1. List initial atom counts: LHS has Fe=1, H=2, O=1. RHS has Fe=3, H=2, O=4. Oxygen and iron are unbalanced. 2. Start with the compound having the maximum number of atoms — on the product side has 4 oxygen atoms. 3. To balance oxygen, multiply by 4: . Now LHS: O=4 (balanced), H=8. 4. To balance hydrogen (8 on LHS, 2 on RHS), multiply by 4: . Now H=8 on both sides (balanced). 5. To balance iron (1 on LHS, 3 on RHS), multiply Fe by 3: . 6. Final check — LHS: Fe=3, H=8, O=4. RHS: Fe=3, H=8, O=4. Balanced. 7. State symbols — iron is a solid metal (s), steam is gaseous water (g), (magnetite) is a solid (s), and hydrogen is a gas (g). The final form: . H₂O is written as (g) because this reaction uses steam. This notation makes the equation more informative by specifying the condition of each reactant and product.
Key Points
- Step-wise approach: balance oxygen first (multiply H₂O by 4), then hydrogen (multiply H₂ by 4), then iron (multiply Fe by 3)
- Always start with the compound containing the most atoms ( has 7 atoms)
- State symbols: (s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous solution
- Final:
- is (g) because steam, not liquid water, is used in this reaction
Common Mistakes
- Changing the subscripts within or to balance (only coefficients can be changed)
- Writing for this reaction — the reaction uses steam, so the state symbol must be (g)
Related Questions
Q4
State the law of conservation of mass. Why must a chemical equation be balanced? Give an example of an unbalanced (skeletal) equation and show how it is balanced.
Q3