Question

Which balanced equation represents a chemical change?

1. H₂O(ℓ) + energy → H₂O(g)
2. 2H₂O(ℓ) + energy → 2H₂(g) + O₂(g)
3. H₂O(ℓ) → H₂O(s) + energy
4. H₂O(g) → H₂O(ℓ) + energy

Answer 1

Option 2 represents a chemical change, where water is separated into hydrogen and oxygen gas. Options 1, 3, and 4 depict physical changes. Equations a and c are not balanced, while equation b is balanced.

Step-by-step explanation:

The question asks which balanced equation represents a chemical change. A chemical change is a process where substances transform into different substances with new chemical properties. Out of the given options, the balanced equation that represents a chemical change is Option 2: 2H2O(ℓ) + energy → 2H2(g) + O2(g). This equation describes the electrolysis of water, a chemical process that separates water into hydrogen and oxygen gas. In contrast, Options 1, 3, and 4 describe physical changes where only the state of water changes, not its chemical composition.

Now, to address the other part of the question regarding the balance of chemical equations. The given chemical equations are:

• a. 2Hg(ℓ) + O2(g) → Hg2O2 (s)
• b. C2H4(g) + 2O2(g) → 2CO2(g) + 2H2O(l)
• c. Mg(NO3)2(s) + 2Li(s) → Mg(s) + 2LiNO3(s)

To determine if the chemical equations are balanced, we compare the number of atoms of each element on both sides of the reaction. Equation b is balanced as written. Equations a and c are not balanced as the number of atoms for each element on the reactant and product sides do not match.