NCEA Level 2 Chemistry Practice Exam 2025 – Your All-in-One Study Guide for Success!

The balanced chemical equation for the complete combustion of methane, which is CH₄, involves the reaction of methane with oxygen to produce carbon dioxide and water. In a balanced equation, the number of atoms of each element must be the same on both the reactant and product sides.

In the case of option B, the equation is:

CH₄ + 2 O₂ → CO₂ + 2 H₂O

Here’s how this balance works out:

- On the left (reactants), we have one carbon atom from CH₄, four hydrogen atoms from CH₄, and two molecules of O₂ provide four oxygen atoms.

- On the right (products), CO₂ contributes one carbon atom, while 2 H₂O contributes two hydrogen atoms (from each molecule, two hydrogen atoms total). Additionally, the two water molecules contribute two oxygen atoms, and CO₂ adds another two oxygen atoms, bringing the total for oxygen to four.

Thus, every atom is accounted for: one carbon on both sides, four hydrogens from the reaction, and four oxygens from the oxygen gas converted into carbon dioxide and water.

This balancing confirms that option B accurately represents the combustion of methane, ensuring that the law of conservation of mass