Complete And Balance Each Of The Following Reactions

Balancing chemical equations is a fundamental skill in chemistry. A balanced equation accurately represents the number of atoms and molecules involved in a chemical reaction, ensuring the law of conservation of mass is upheld. The process can seem daunting at first, but with a systematic approach and understanding of the principles, it becomes a manageable and even enjoyable task. This comprehensive guide will walk you through the process of balancing chemical equations, including various reaction types, with clear examples and explanations to build your confidence and mastery.

Understanding Chemical Equations

Before diving into the balancing process, it's essential to understand the components of a chemical equation:

Reactants: The substances that are initially involved in the reaction (on the left side of the equation).
Products: The substances that are formed as a result of the reaction (on the right side of the equation).
Coefficients: The numbers placed in front of the chemical formulas of reactants and products. These numbers indicate the relative amounts of each substance involved in the reaction. Coefficients are the only values you can change when balancing an equation.
Subscripts: The numbers within a chemical formulas that indicate the number of atoms of each element in a molecule. You cannot change subscripts when balancing equations. Changing subscripts alters the chemical identity of the substance.
States of Matter: Often indicated in parentheses after each formula: (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous (dissolved in water). These states do not affect the balancing process but provide additional information about the reaction.
Arrow (→): Represents the direction of the reaction, indicating that reactants are transformed into products.

The Goal of Balancing:

The primary goal of balancing a chemical equation is to ensure that the number of atoms of each element is the same on both sides of the equation. This adheres to the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction.

The Systematic Approach to Balancing

Here's a step-by-step approach to balancing chemical equations effectively:

Write the Unbalanced Equation: Identify the reactants and products and write the chemical formulas for each. Make sure you write correct chemical formulas, as this is the base of your chemical equation.
Count Atoms: Count the number of atoms of each element on both the reactant and product sides of the equation. List each element and the corresponding number of atoms.
Balance Elements One at a Time: Begin by balancing the elements that appear in only one reactant and one product. It's often helpful to start with metals and then move on to nonmetals. Leave hydrogen and oxygen for last, as they often appear in multiple compounds.
Use Coefficients: Place coefficients in front of the chemical formulas to adjust the number of atoms of each element. Remember, you can only change the coefficients, not the subscripts.
Check Your Work: After adjusting the coefficients, recount the number of atoms of each element on both sides of the equation. Verify that the equation is balanced – the number of atoms of each element should be the same on both sides.
Simplify Coefficients (If Necessary): If all the coefficients are divisible by a common factor, divide them by that factor to obtain the simplest whole-number ratio.
Include States of Matter (Optional): Add the states of matter (s, l, g, aq) to each compound if the information is provided.

Balancing Different Types of Reactions

Let's apply these steps to balance various types of chemical reactions, including synthesis, decomposition, single displacement, double displacement, and combustion reactions.

1. Synthesis Reactions

In a synthesis reaction, two or more reactants combine to form a single product.

Example: Sodium (Na) reacts with chlorine gas (Cl₂) to form sodium chloride (NaCl).

Unbalanced Equation:

Na (s) + Cl₂ (g) → NaCl (s)
Count Atoms:
- Reactants: Na = 1, Cl = 2
- Products: Na = 1, Cl = 1
Balance Chlorine: Place a coefficient of 2 in front of NaCl to balance the chlorine atoms.

Na (s) + Cl₂ (g) → 2 NaCl (s)
Balance Sodium: Now, there are 2 sodium atoms on the product side, so place a coefficient of 2 in front of Na on the reactant side.

2 Na (s) + Cl₂ (g) → 2 NaCl (s)
Check Your Work:
- Reactants: Na = 2, Cl = 2
- Products: Na = 2, Cl = 2
The equation is now balanced.

2. Decomposition Reactions

In a decomposition reaction, a single reactant breaks down into two or more products.

Example: Potassium chlorate (KClO₃) decomposes into potassium chloride (KCl) and oxygen gas (O₂).

Unbalanced Equation:

KClO₃ (s) → KCl (s) + O₂ (g)
Count Atoms:
- Reactants: K = 1, Cl = 1, O = 3
- Products: K = 1, Cl = 1, O = 2
Balance Oxygen: To balance oxygen, find the least common multiple (LCM) of 3 and 2, which is 6. Place a coefficient of 2 in front of KClO₃ and a coefficient of 3 in front of O₂.

2 KClO₃ (s) → KCl (s) + 3 O₂ (g)
Balance Potassium and Chlorine: Now, there are 2 potassium and 2 chlorine atoms on the reactant side, so place a coefficient of 2 in front of KCl on the product side.

2 KClO₃ (s) → 2 KCl (s) + 3 O₂ (g)
Check Your Work:
- Reactants: K = 2, Cl = 2, O = 6
- Products: K = 2, Cl = 2, O = 6
The equation is now balanced.

3. Single Displacement Reactions

In a single displacement reaction, one element replaces another element in a compound.

Example: Zinc (Zn) reacts with hydrochloric acid (HCl) to form zinc chloride (ZnCl₂) and hydrogen gas (H₂).

Unbalanced Equation:

Zn (s) + HCl (aq) → ZnCl₂ (aq) + H₂ (g)
Count Atoms:
- Reactants: Zn = 1, H = 1, Cl = 1
- Products: Zn = 1, H = 2, Cl = 2
Balance Hydrogen and Chlorine: Place a coefficient of 2 in front of HCl to balance the hydrogen and chlorine atoms.

Zn (s) + 2 HCl (aq) → ZnCl₂ (aq) + H₂ (g)
Check Your Work:
- Reactants: Zn = 1, H = 2, Cl = 2
- Products: Zn = 1, H = 2, Cl = 2
The equation is now balanced.

4. Double Displacement Reactions

In a double displacement reaction, the positive and negative ions of two compounds exchange places.

Example: Silver nitrate (AgNO₃) reacts with sodium chloride (NaCl) to form silver chloride (AgCl) and sodium nitrate (NaNO₃).

Unbalanced Equation:

AgNO₃ (aq) + NaCl (aq) → AgCl (s) + NaNO₃ (aq)
Count Atoms:
- Reactants: Ag = 1, N = 1, O = 3, Na = 1, Cl = 1
- Products: Ag = 1, N = 1, O = 3, Na = 1, Cl = 1
Notice that all elements are already balanced.
Balanced Equation:

AgNO₃ (aq) + NaCl (aq) → AgCl (s) + NaNO₃ (aq)

This equation is already balanced!

5. Combustion Reactions

Combustion reactions involve the rapid reaction between a substance with an oxidant, usually oxygen, to produce heat and light. Combustion reactions often involve hydrocarbons (compounds containing carbon and hydrogen) and produce carbon dioxide (CO₂) and water (H₂O). Balancing combustion reactions can be trickier than other types, so a specific strategy is helpful:

Balance Carbon: Balance the carbon atoms first. Place a coefficient in front of CO₂ to match the number of carbon atoms in the hydrocarbon.
Balance Hydrogen: Balance the hydrogen atoms next. Place a coefficient in front of H₂O to match the number of hydrogen atoms in the hydrocarbon.
Balance Oxygen: Balance the oxygen atoms last. Count the total number of oxygen atoms on the product side (from both CO₂ and H₂O) and place a coefficient in front of O₂ to match this number.
Adjust Coefficients (If Necessary): If the coefficient for O₂ is a fraction, multiply all coefficients in the equation by 2 to obtain whole numbers.

Example: Combustion of methane (CH₄)

Unbalanced Equation:

CH₄ (g) + O₂ (g) → CO₂ (g) + H₂O (g)
Balance Carbon: There is 1 carbon atom on both sides, so carbon is already balanced.
Balance Hydrogen: There are 4 hydrogen atoms on the reactant side, so place a coefficient of 2 in front of H₂O.

CH₄ (g) + O₂ (g) → CO₂ (g) + 2 H₂O (g)
Balance Oxygen: Now, there are 2 oxygen atoms in CO₂ and 2 oxygen atoms in 2 H₂O, for a total of 4 oxygen atoms on the product side. Place a coefficient of 2 in front of O₂ on the reactant side.

CH₄ (g) + 2 O₂ (g) → CO₂ (g) + 2 H₂O (g)
Check Your Work:
- Reactants: C = 1, H = 4, O = 4
- Products: C = 1, H = 4, O = 4
The equation is now balanced.

Example: Combustion of ethane (C₂H₆)

Unbalanced Equation:

C₂H₆ (g) + O₂ (g) → CO₂ (g) + H₂O (g)
Balance Carbon: There are 2 carbon atoms on the reactant side, so place a coefficient of 2 in front of CO₂.

C₂H₆ (g) + O₂ (g) → 2 CO₂ (g) + H₂O (g)
Balance Hydrogen: There are 6 hydrogen atoms on the reactant side, so place a coefficient of 3 in front of H₂O.

C₂H₆ (g) + O₂ (g) → 2 CO₂ (g) + 3 H₂O (g)
Balance Oxygen: Now, there are 4 oxygen atoms in 2 CO₂ and 3 oxygen atoms in 3 H₂O, for a total of 7 oxygen atoms on the product side. To get 7 oxygen atoms on the reactant side, we would need a coefficient of 3.5 in front of O₂.

C₂H₆ (g) + 3.5 O₂ (g) → 2 CO₂ (g) + 3 H₂O (g)
Adjust Coefficients: Since we want whole number coefficients, multiply all coefficients by 2:

2 C₂H₆ (g) + 7 O₂ (g) → 4 CO₂ (g) + 6 H₂O (g)
Check Your Work:
- Reactants: C = 4, H = 12, O = 14
- Products: C = 4, H = 12, O = 14
The equation is now balanced.

Advanced Tips and Tricks

Polyatomic Ions: If a polyatomic ion (such as SO₄²⁻, NO₃⁻, PO₄³⁻) remains unchanged on both sides of the equation, treat it as a single unit when balancing.
Fractional Coefficients: As seen in the combustion example, you may need to use fractional coefficients temporarily. To eliminate fractions, multiply the entire equation by the denominator of the fraction.
Trial and Error: Sometimes, balancing an equation requires a bit of trial and error. Don't be afraid to erase and try different coefficients until you find the right combination.
Practice, Practice, Practice: The more you practice balancing chemical equations, the easier it will become.

Common Mistakes to Avoid

Changing Subscripts: Remember, never change the subscripts in a chemical formula. This changes the identity of the substance.
Incorrect Chemical Formulas: Make sure you have the correct chemical formulas for all reactants and products. A mistake in the formula will make it impossible to balance the equation correctly.
Forgetting to Check: Always double-check your work after balancing to ensure that the number of atoms of each element is the same on both sides of the equation.

Examples and Exercises

Here are some additional examples and exercises for you to practice:

Example 1: Balance the following equation:

Fe₂O₃ (s) + CO (g) → Fe (s) + CO₂ (g)

Balanced Equation: Fe₂O₃ (s) + 3 CO (g) → 2 Fe (s) + 3 CO₂ (g)

Example 2: Balance the following equation:

C₆H₁₂O₆ → C₂H₅OH + CO₂

Balanced Equation: C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂

Exercises:

Balance: N₂ (g) + H₂ (g) → NH₃ (g)
Balance: Mg (s) + O₂ (g) → MgO (s)
Balance: H₂SO₄ (aq) + NaOH (aq) → Na₂SO₄ (aq) + H₂O (l)
Balance: C₄H₁₀ (g) + O₂ (g) → CO₂ (g) + H₂O (g)

FAQ

Q: Why is balancing chemical equations important?

Balancing chemical equations is crucial because it ensures that the equation accurately represents the conservation of mass in a chemical reaction. It also provides the correct stoichiometric ratios between reactants and products, which are essential for quantitative calculations in chemistry.

Q: What if I can't balance an equation?

If you're struggling to balance an equation, double-check that you have the correct chemical formulas for all reactants and products. Also, make sure you're following a systematic approach, starting with elements that appear in only one reactant and one product. If you're still having trouble, try using a different strategy or seeking help from a tutor or online resource.

Q: Is there an easier way to balance complex equations?

For complex equations, you can use algebraic methods or matrix methods to solve for the coefficients. These methods involve setting up a system of equations based on the conservation of atoms and solving for the unknown coefficients. However, for most introductory chemistry courses, the trial-and-error method is sufficient.

Q: Can I change the subscripts in a chemical formula to balance an equation?

No, you should never change the subscripts in a chemical formula when balancing an equation. Changing the subscripts changes the chemical identity of the substance. You can only adjust the coefficients in front of the chemical formulas.

Conclusion

Balancing chemical equations is a fundamental skill in chemistry that requires a systematic approach and a solid understanding of chemical principles. By following the steps outlined in this guide and practicing regularly, you can master the art of balancing equations and gain a deeper understanding of chemical reactions. Remember to always double-check your work and avoid common mistakes. With persistence and practice, you'll become proficient at balancing even the most complex chemical equations.