Why is it difficult to experimentally prove the law of conservation of mass when a chemical reaction produces a gas?

• A. Because the gas may escape from the reaction vessel, making it hard to measure its mass accurately.
• B. Because the law of conservation of mass does not apply to reactions involving gases.
• C. Because gases do not have mass and therefore cannot be measured.
• D. Because gases always react with the atmosphere, changing their mass.

Answer: (A)

Verified step by step guidance

1. Understand the law of conservation of mass: it states that in a closed system, the total mass of reactants equals the total mass of products during a chemical reaction.
2. Recognize that when a chemical reaction produces a gas, the gas may escape from the reaction vessel if it is not perfectly sealed.
3. If the gas escapes, the system is no longer closed, and the mass measured inside the vessel will appear to decrease, even though the total mass (including the escaped gas) remains constant.
4. This loss of gas from the system makes it difficult to experimentally verify the law of conservation of mass because the escaping gas's mass is not accounted for in the measurement.
5. Therefore, to accurately prove the law of conservation of mass in reactions producing gases, the reaction must be conducted in a closed system that prevents gas from escaping.