Which Of The Following Are Balanced Equations

Which of the Following Are Balanced Equations? A Complete Guide to Identifying and Verifying Chemical Balance

When studying chemistry, one of the first skills you must master is recognizing whether a chemical equation is balanced. A balanced equation obeys the law of conservation of mass, meaning the number of each type of atom on the reactant side equals the number on the product side. If you encounter a list of equations and are asked, “which of the following are balanced equations?” you need a reliable method to evaluate each one quickly and accurately. This article walks you through the concept, provides step‑by‑step procedures, offers plenty of examples, and includes practice problems so you can confidently answer that question every time.

Understanding Balanced Chemical Equations

A chemical equation is a symbolic representation of a reaction, showing the reactants that combine to form the products. For the equation to be scientifically valid, it must be balanced. Balancing ensures that mass is neither created nor destroyed during the reaction, reflecting the fundamental principle that atoms are conserved.

In a balanced equation:

• Each element’s atom count is identical on both sides.
• Coefficients (the numbers placed before formulas) may be adjusted to achieve balance, but subscripts within a chemical formula cannot be changed because they define the substance’s identity.
• The total charge must also be balanced in ionic or redox reactions.

If any of these conditions fail, the equation is unbalanced and does not correctly depict the reaction’s stoichiometry.

Steps to Check if an Equation Is Balanced

Follow this systematic procedure to determine whether a given equation is balanced. You can apply it to simple molecular equations, ionic equations, or even complex redox reactions.

1. List All Elements Present

Write down every distinct element that appears in the reactants and products. If the reaction involves polyatomic ions that remain unchanged, you may treat the entire ion as a single unit to simplify counting.

2. Count Atoms of Each Element on Both Sides

For each element (or polyatomic ion), tally the number of atoms contributed by every molecule or ion. Remember to multiply subscripts by the coefficient in front of the formula.

3. Compare the Tallies

If the counts match for every element (or ion), the equation is balanced. If any mismatch exists, the equation is unbalanced.

4. Adjust Coefficients (If You Need to Balance It)

When you are tasked with balancing an unbalanced equation, start with the most complex molecule, adjust coefficients to match atom counts, and proceed iteratively. Never change subscripts.

5. Verify Charge Balance (For Ionic Equations)

Sum the charges of all reactants and compare to the sum of all product charges. They must be equal.

Quick Checklist- Elements: Atom counts equal? - Polyatomic ions (if unchanged): Counts equal?

• Charge: Net charge equal?
• Coefficients: Smallest whole‑number set preferred?

If you answer “yes” to all, you have a balanced equation.

Common Examples and Non‑Examples

Below are several equations frequently encountered in introductory chemistry. Examine each to see why it is balanced or not.

Example 1: Combustion of Methane

[ \text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O} ]

• Carbon: 1 (reactant) = 1 (product)
• Hydrogen: 4 (reactant) = 2×2 = 4 (product)
• Oxygen: 2×2 = 4 (reactant) = 2 (in CO₂) + 2×1 (in H₂O) = 4

All counts match → Balanced.

Example 2: Formation of Ammonia (Haber Process)

[ \text{N}_2 + 3\text{H}_2 \rightarrow 2\text{NH}_3 ]

• Nitrogen: 2 = 2
• Hydrogen: 3×2 = 6 = 2×3 = 6

Balanced.

Example 3: Unbalanced Equation – Sodium Chloride Formation

[ \text{Na} + \text{Cl}_2 \rightarrow \text{NaCl} ]

• Sodium: 1 = 1 (OK)
• Chlorine: 2 (reactant) ≠ 1 (product)

Chlorine atoms are not conserved → Unbalanced. The balanced version is (2\text{Na} + \text{Cl}_2 \rightarrow 2\text{NaCl}).

Example 4: Ionic Equation – Precipitation of Silver Chloride

[ \text{Ag}^+ (aq) + \text{Cl}^- (aq) \rightarrow \text{AgCl} (s) ]

• Silver: 1 = 1
• Chloride: 1 = 1
• Charge: (+1) + (‑1) = 0; product is neutral → 0

Balanced.

Example 5: Redox Reaction – Reaction of Zinc with Hydrochloric Acid

[ \text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2 ]

• Zinc: 1 = 1
• Hydrogen: 2×1 = 2 = 2 (in H₂)
• Chlorine: 2 = 2 Balanced.

These illustrations show how a quick atom‑by‑atom check reveals the balance status.

Practice Problems: Which of the Following Are Balanced Equations?

Now apply the method to a set of equations. For each, decide Yes (balanced) or No (unbalanced). The answer key follows the list.

Practice Problems: Which of theFollowing Are Balanced Equations? (Continued)

Now apply the method to a set of equations. For each, decide Yes (balanced) or No (unbalanced). The answer key follows the list.

Answers Explained

1. C₂H₆ + ⁷/₂O₂ → 2CO₂ + 3H₂O

   • Carbon: 2 (reactant) = 2 (product)
   • Hydrogen: 6 (reactant) = 6 (product)
   • Oxygen: ⁷/₂ × 2 = 7 (reactant) = 2 (in CO₂) + 3 (in H₂O) = 5? Wait, 2+3=5, but we need 7. No, this is unbalanced.
     (Correction: The oxygen count is incorrect. 2CO₂ has 4 O atoms, 3H₂O has 3 O atoms, total 7 O atoms. Reactant O₂ has 7 atoms (7/2 molecules × 2 atoms each). So it is balanced. Verdict: Yes.)
     (Note: The initial explanation in the answer key was incorrect. The equation is balanced as written. The oxygen atoms: 7/2 O₂ provides 7 O atoms. Products: 2CO₂ (4 O) + 3H₂O (3 O) = 7 O atoms. All other atoms match. It is the balanced equation for ethane combustion, often written with a fraction for O₂.)

2. Fe + O₂ → Fe₂O₃

   • Iron: 1 (reactant) ≠ 2 (product)
   • Oxygen: 2 (reactant) ≠ 3 (product)
   • Charge: Not applicable (elements).
   • Polyatomic Ions: Not applicable.
   • Coefficients: Smallest whole number set? Not yet balanced.
   • Conclusion: Iron atoms and oxygen atoms are not conserved. Unbalanced.

3. 2KClO₃ → 2KCl + 3O₂

   • Potassium: 2 = 2
   • Chlorine: 2 = 2
   • Oxygen: 3×2 = 6 (reactant) = 3 (in O₂)
   • Charge: Not applicable (all neutral