Question detail
In a thermal decomposition reaction of a metal carbonate, why does it appear to lose mass?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations
Question
- A. The metal carbonate absorbs heat
- B. Carbon dioxide gas escapes into the atmosphere
- C. The metal carbonate gains mass from the surroundings
- D. The reaction is incomplete
Answer
Carbon dioxide gas escapes into the atmosphere
Explanation
As carbon dioxide gas is produced and escapes, the total mass of the remaining substances appears to decrease.
Common mistake
Misunderstanding Mass Change
Students often think that mass is lost when a gas escapes during a reaction, rather than understanding that the total mass remains constant.
To fix this, students should remember that the law of conservation of mass states that no atoms are lost or created, and they should consider the mass of the gas that escapes as part of the total mass of the system. Keep the correction anchored to Mass changes when a reactant or product is a gas; check formula, substitution, calculation, final answer, and unit where relevant.
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