Which observation best supports the Law of Conservation of Mass when dry ice (solid CO_2) changes into a gas?

• A. The volume of the container increases as the dry ice sublimates.
• B. The temperature of the container decreases during the process.
• C. The total mass of the closed container and its contents remains constant before and after sublimation.
• D. The color of the container changes as the dry ice turns into gas.

Answer: (C)

Verified step by step guidance

1. Understand the Law of Conservation of Mass, which states that mass cannot be created or destroyed in a closed system during a chemical or physical change.
2. Identify that sublimation is a physical change where dry ice (solid CO_2) changes directly into carbon dioxide gas without passing through the liquid phase.
3. Recognize that in a closed container, no matter can enter or leave, so the total mass of the container plus its contents should remain constant throughout the sublimation process.
4. Evaluate the observations: changes in volume, temperature, or color do not directly indicate mass conservation, but measuring the total mass before and after sublimation in a closed system does.
5. Conclude that the observation best supporting the Law of Conservation of Mass is that the total mass of the closed container and its contents remains constant before and after the dry ice sublimates.