Question detail
For Mass changes when a reactant or product is a gas, which option best supports this Unit 4.3 objective: Use a balanced symbol equation to explain observed mass changes in a non-enclosed system?
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 mass decreases because gas escapes.
- B. The mass increases due to gas uptake.
- C. The mass remains constant regardless of gas production.
- D. The mass changes only if the reaction is exothermic.
Answer
The correct option is The mass decreases because gas escapes..
Explanation
The correct option is The mass decreases because gas escapes.. The mass decreases because gas escapes. is correct because it directly supports the approved learning objective to use a balanced symbol equation to explain observed mass changes in a non-enclosed system. The reasoning belongs to Mass changes when a reactant or product is a gas within Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations, so it should not be confused with nearby quantitative ideas such as mass, moles, concentration, yield, atom economy, or gas volume unless those are named in the objective. Use the focus term mass change to keep the answer aligned with AQA GCSE Chemistry 8462 Unit 4.3. The other options are weaker because they either use the wrong formula, the wrong unit, a vague relationship, or the wrong quantitative context.
Common mistake
Misunderstanding Mass Changes
Students often think that mass is lost when a gas escapes in a reaction, without considering the balanced equation.
To fix this, students should use a balanced symbol equation to account for all reactants and products, ensuring they recognize that the total mass remains constant even if a gas is released. 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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