Which of the following chemical equations is unbalanced?

• A. H_2 + H_2 + O_2 ightarrow H_2O + H_2O
• B. C + O_2 ightarrow CO_2
• C. Sr + O_2 ightarrow 2SrO
• D. 6H_2 + 3O_2 ightarrow 6H_2O

Answer: (A)

Verified step by step guidance

1. Step 1: Understand that a balanced chemical equation has the same number of atoms of each element on both sides of the reaction arrow.
2. Step 2: For each equation, count the number of atoms of each element on the reactant side and compare it to the number on the product side.
3. Step 3: For the equation \(H_2 + H_2 + O_2 \rightarrow H_2O + H_2O\), count the atoms: Reactants have 4 hydrogen atoms (2 + 2) and 2 oxygen atoms; Products have 4 hydrogen atoms (2 per \(H_2O\) times 2) but only 2 oxygen atoms total (1 per \(H_2O\) times 2). Check if these counts match.
4. Step 4: Repeat the atom count for the other equations: \(C + O_2 \rightarrow CO_2\), \(Sr + O_2 \rightarrow 2SrO\), and \$6H_2 + 3O_2 \rightarrow 6H_2O$, verifying that the number of atoms for each element is equal on both sides.
5. Step 5: Identify which equation does not have equal numbers of atoms on both sides, indicating it is unbalanced.