Which of the Following Is a Correctly Balanced Equation?
Balancing chemical equations is a fundamental skill in chemistry that ensures the law of conservation of mass is obeyed. Now, when atoms are conserved, the number of atoms of each element on the reactant side must equal the number on the product side. This article walks through the logic behind balancing equations, demonstrates common pitfalls, and provides a step‑by‑step analysis of several sample reactions to determine which one is correctly balanced The details matter here..
Short version: it depends. Long version — keep reading.
Introduction
In chemistry, an equation is more than a symbolic representation; it is a statement of a chemical transformation that must satisfy a strict rule: mass conservation. Here's the thing — an unbalanced equation can lead to erroneous predictions about stoichiometry, energy changes, and product yields. Which means, chemists routinely check that every equation is balanced before using it in calculations or experimental design.
It sounds simple, but the gap is usually here.
The question “Which of the following is a correctly balanced equation?But ” is a typical problem found in textbooks and exams. It tests not only memorization of reaction types but also the ability to apply algebraic reasoning to count atoms. Below, we break down the balancing process, illustrate it with concrete examples, and explain how to spot the correct answer among a set of alternatives.
The Balancing Process Explained
1. Write the Skeleton Equation
The skeleton equation lists the reactants and products without coefficients:
[ \text{A} + \text{B} \rightarrow \text{C} + \text{D} ]
2. Count Atoms of Each Element
Create a table that tallies the number of atoms for every element on both sides. Take this case: in the reaction between nitrogen and hydrogen to form ammonia:
[ \text{N}_2 + \text{H}_2 \rightarrow \text{NH}_3 ]
The counts are:
| Element | Reactants | Products |
|---|---|---|
| N | 2 | 1 |
| H | 2 | 3 |
3. Assign Coefficients
Introduce variables (e.g., (a, b, c, d)) as coefficients in front of each compound.
[ \begin{cases} 2a = c \ 2b = 3c \end{cases} ]
Solve for the smallest whole‑number coefficients that satisfy all equations Simple, but easy to overlook..
4. Verify the Balance
After assigning coefficients, recalculate the atom counts to confirm equality on both sides. If any element is unbalanced, adjust coefficients and repeat And that's really what it comes down to..
Common Mistakes to Avoid
| Mistake | Why It Happens | How to Fix It |
|---|---|---|
| Using fractions | Some students stop at fractional coefficients. Consider this: | |
| Neglecting to balance all elements | Focus may drift to the most obvious imbalance. | Systematically check every element, even those that appear balanced at first glance. |
| Ignoring stoichiometric constraints | For reactions involving polyatomic ions, the overall charge may be overlooked. | Multiply all coefficients by the least common denominator to obtain whole numbers. Think about it: |
| Assuming the first solution is correct | Multiple sets of coefficients can satisfy the equations. | Choose the set with the smallest whole numbers (the simplest form). |
Sample Reactions and Analysis
Below are four reactions commonly presented in coursework. We will determine which one is correctly balanced.
-
Reaction A
[ \text{C}_2\text{H}_6 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} ] -
Reaction B
[ 2\text{Fe} + 3\text{O}_2 \rightarrow 2\text{Fe}_2\text{O}_3 ] -
Reaction C
[ \text{NaOH} + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O} ] -
Reaction D
[ 4\text{H}_2\text{O} \rightarrow 2\text{H}_2 + 2\text{O}_2 ]
Let’s examine each one.
Reaction A: Ethane Combustion
Skeleton:
[
\text{C}_2\text{H}_6 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O}
]
Atom Counts (before coefficients):
| Element | Reactants | Products |
|---|---|---|
| C | 2 | 1 |
| H | 6 | 2 |
| O | 2 | 3 |
Assign Coefficients:
Let (a) be the coefficient for (\text{C}_2\text{H}_6), (b) for (\text{O}_2), (c) for (\text{CO}_2), (d) for (\text{H}_2\text{O}).
Equations: [ \begin{aligned} 2a &= c \ 6a &= 2d \ 2b &= 3c + d \end{aligned} ]
Choosing (a = 1) gives (c = 2) and (d = 3). Plugging into the oxygen equation: [ 2b = 3(2) + 3 = 9 \Rightarrow b = 4.5 ] Since coefficients must be whole numbers, multiply all by 2: [ 2\text{C}_2\text{H}_6 + 9\text{O}_2 \rightarrow 4\text{CO}_2 + 6\text{H}_2\text{O} ]
And yeah — that's actually more nuanced than it sounds Simple, but easy to overlook..
Conclusion:
Reaction A as written is not balanced. The correct balanced form requires coefficients 2, 9, 4, and 6.
Reaction B: Iron Oxidation
Skeleton:
[
2\text{Fe} + 3\text{O}_2 \rightarrow 2\text{Fe}_2\text{O}_3
]
Check Atom Counts:
| Element | Reactants | Products |
|---|---|---|
| Fe | (2 \times 1 = 2) | (2 \times 2 = 4) |
| O | (3 \times 2 = 6) | (2 \times 3 = 6) |
Fe is unbalanced: 2 vs. 4. To balance Fe, change the coefficient of Fe on the reactant side to 4:
[ 4\text{Fe} + 3\text{O}_2 \rightarrow 2\text{Fe}_2\text{O}_3 ]
Now Fe: 4 = 4, O: 6 = 6. Reaction B, as given, is not balanced Worth keeping that in mind..
Reaction C: Neutralization
Skeleton:
[
\text{NaOH} + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O}
]
Atom Counts:
| Element | Reactants | Products |
|---|---|---|
| Na | 1 | 1 |
| O | 1 | 1 |
| H | 1 + 1 = 2 | 2 |
| Cl | 1 | 1 |
All elements are balanced. Coefficients are all 1. Reaction C is correctly balanced.
Reaction D: Electrolysis of Water
Skeleton:
[
4\text{H}_2\text{O} \rightarrow 2\text{H}_2 + 2\text{O}_2
]
Atom Counts:
| Element | Reactants | Products |
|---|---|---|
| H | (4 \times 2 = 8) | (2 \times 2 = 4) + (0 = 4) |
| O | (4 \times 1 = 4) | (2 \times 2 = 4) |
Hydrogen is unbalanced (8 vs. 4). To correct, double the coefficient of (\text{H}_2):
[ 4\text{H}_2\text{O} \rightarrow 4\text{H}_2 + 2\text{O}_2 ]
Now H: 8 = 8, O: 4 = 4. Reaction D, as written, is not balanced.
Which Equation Is Correctly Balanced?
From the analysis above, Reaction C (the neutralization of sodium hydroxide with hydrochloric acid) is the only one that is already balanced with integer coefficients. The other reactions require adjustment of coefficients to satisfy mass conservation It's one of those things that adds up. Surprisingly effective..
Frequently Asked Questions
1. Why do some balanced equations use fractional coefficients?
Fractional coefficients can arise when the simplest set of integers is not immediately apparent. Multiplying all coefficients by the denominator of the fractions yields an equivalent balanced equation with whole numbers, which is the preferred form Not complicated — just consistent..
2. Do I need to balance charges in redox reactions?
Yes. In redox reactions, balancing electrons (or charges) is essential. While the atom count ensures mass conservation, charge balance ensures electrical neutrality, especially in aqueous solutions.
3. Can a balanced equation be wrong if the reaction doesn't actually occur?
A mathematically balanced equation may represent a possible reaction, but it might be kinetically unfavorable or thermodynamically impossible. Chemistry balances constraints of both mass and energy.
4. How do I handle polyatomic ions that stay together?
Treat the polyatomic ion as a single unit when counting atoms. To give you an idea, in (\text{CaSO}_4), count one calcium, one sulfur, and four oxygens as one compound.
5. Is there software that can balance equations automatically?
Yes, many computational tools and calculators can balance equations. That said, understanding the underlying principles is crucial for interpreting results and troubleshooting errors.
Conclusion
Balancing chemical equations is a disciplined exercise that reinforces the conservation of mass principle. By systematically counting atoms, assigning coefficients, and verifying balance, chemists can confidently write equations that reflect real chemical processes. But among the sample reactions examined, Reaction C stands out as the correctly balanced equation. Mastery of this skill not only prepares students for academic assessments but also equips them with a foundational tool for research, industry, and everyday problem-solving in chemistry But it adds up..
