Question detail
In a closed flask, magnesium reacts with oxygen and no gas escapes. Which statement correctly applies conservation of 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 total mass stays the same because atoms are rearranged, not created or destroyed.
- B. The mass increases because oxygen atoms are made during the reaction.
- C. The mass decreases because reactant atoms disappear when product forms.
- D. The mass changes unpredictably because a new substance has different properties.
Answer
The correct option is: the total mass stays the same because atoms are rearranged, not created or destroyed. This answer should be checked against the named quantitative relationship, the balanced equation where relevant, and the final unit required by the question.
Explanation
In a closed system, no matter enters or leaves, so the total mass of reactants equals the total mass of products. The atoms are conserved; they are simply rearranged into new substances. This question is about conservation of mass in a closed container, not about gas loss or measurement error.
Common mistake
Mass Misunderstanding
Students often think that the mass of products can differ from the mass of reactants in a chemical reaction.
Emphasize that according to the law of conservation of mass, the total mass of reactants must equal the total mass of products in a closed system.
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