Explain why the thermal decomposition of a metal carbonate may appear to lose mass when carbon dioxide escapes.

During the thermal decomposition of a metal carbonate, the compound breaks down into a metal oxide and carbon dioxide gas. As the carbon dioxide gas escapes into the atmosphere, the total mass of the remaining solid product appears to decrease, even though no atoms are lost in the reaction.

This question tests the understanding of mass changes in chemical reactions, specifically focusing on the escape of gas. It highlights the concept of conservation of mass, as students must connect the loss of mass to the release of carbon dioxide, demonstrating their grasp of the particle model and chemical processes.