Final answer:
The correct answer to the chemical reaction question in a closed system is that the total mass of the particles in the system stays the same, due to the law of conservation of mass.
Step-by-step explanation:
When methane reacts with oxygen in a closed system to form carbon dioxide and water, one of the foundational principles of chemical reactions is conserved: the law of conservation of mass. As the reaction progresses, neither the total number of particles nor the total mass of the particles increases or decreases. The total mass of the system remains constant according to this law.
In a balanced chemical equation, the number of atoms for each element is the same on the reactant side as on the product side. For the reaction between methane (CH₄) and oxygen (O₂), yielding carbon dioxide (CO₂) and water (H₂O), even though the number and type of molecules may change, the total mass is conserved.
Therefore, the correct answer is:
C. The total mass of the particles in the system stays the same.