Final answer:
The correct coefficient for O2 that demonstrates the Law of Conservation of Mass is 1. By balancing the equation with this coefficient, the number of atoms of each element on both sides is equal, thus adhering to the law that matter is neither created nor destroyed.
Step-by-step explanation:
To determine which coefficient for O2 demonstrates the Law of Conservation of Mass in a chemical equation, we must balance the equation such that the number of atoms of each element is equal on both sides. For balancing the given equation, 2 H2(g) + O2(g) → 2 H2O(l), we can see that by placing a coefficient of 1 in front of O2, we achieve a balance of four hydrogen atoms and two oxygen atoms on both sides. This satisfies the Law of Conservation of Mass, which states that matter cannot be created or destroyed in a chemical reaction, only rearranged. The mass of reactants equals the mass of products, and in this case, both sides have equal numbers of each atom.
An example of the Law of Conservation of Mass in action is the baking of bread dough, where despite the release of gases and aromas during baking, the total mass of the ingredients before and after remains the same if no matter is lost to the surroundings. When magnesium burns in air, the mass of magnesium oxide produced is exactly equal to the mass of magnesium and oxygen that reacted. Likewise, when Antoine Lavoisier conducted his famous experiment with tin and air, the mass of the sealed flask and contents remained the same after heating, demonstrating the law.