Why can a lower measured mass after gas escapes from an open container give a wrong conclusion?
Answer and explanation
Correct answer: Because the gas mass is not included in the later measurement.
The conservation-of-mass law applies to a complete, closed system. In an open container, the gas produced may escape into the surroundings before the final weighing. The balance then measures only the remaining material, not the escaped gas, so the observed mass is lower even though total mass has been conserved. Therefore A is correct. Mass is not destroyed, the reaction need not stop, and a chemical reaction does not become physical merely because gas escapes.
Frequently asked questions
What is the correct answer to this question?
Because the gas mass is not included in the later measurement.
Why is this the correct answer?
The conservation-of-mass law applies to a complete, closed system. In an open container, the gas produced may escape into the surroundings before the final weighing. The balance then measures only the remaining material, not the escaped gas, so the observed mass is lower even though total mass has been conserved. Therefore A is correct. Mass is not destroyed, the reaction need not stop, and a chemical reaction does not become physical merely because gas escapes.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Chemical Reactions and Equations.
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