Kit Library / Science / Chemistry
⚡ Topic Learning KitShared by a Veda learner · Generated with Veda AI
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Atoms don't vanish—they just switch partners.
In any chemical reaction, the total mass of reactants equals the total mass of products. Atoms are rearranged, not created or destroyed.
↳ The law of conservation of mass is the reason we balance chemical equations.
One law, one simple statement.
↳ The law applies to closed systems where no matter escapes.
A French chemist cracked the code.
Antoine Lavoisier established the law of conservation of mass in the late 18th century through careful quantitative experiments.
↳ Lavoisier's precise measurements proved mass is conserved in reactions.
Watch mass balance before your eyes.
↳ Real reactions obey the law—account for all reactants and products.
Escaping gas doesn't break the law.
↳ In open systems, gases can escape, but total mass is still conserved if you include them.
Balance atoms, not just mass.
↳ Balancing equations is a direct application of conservation of mass.
From baking to breathing.
Conservation of mass explains why a sealed bag of reactants weighs the same after a reaction, and why burning fuels requires accounting for gases.
↳ The law is fundamental to cooking, industry, and environmental science.
Balance first, then calculate.
In exams, if a chemical equation is unbalanced, any mass calculation will be wrong. Always balance the equation first.
↳ Balancing equations is a prerequisite for stoichiometry problems.
Reactants in, products out—mass unchanged.
Think of atoms as LEGO bricks: you can build different structures, but the number and type of bricks stay the same.
↳ Atoms are conserved; only their arrangement changes.
Find the missing mass easily.
↳ Use conservation of mass to find unknown quantities in reactions.
Mass-energy is the bigger law.
In nuclear reactions, a tiny amount of mass is converted to energy (E=mc²), so mass alone isn't conserved—but mass-energy is.
↳ Conservation of mass holds for chemical reactions, but nuclear reactions involve mass-energy equivalence.
Where did the gas go?
↳ The law applies to closed systems; open systems require accounting for escaping matter.
Both conserve mass.
↳ Mass is conserved in both physical and chemical changes.
He lost his head, but not his law.
Antoine Lavoisier, who established the law, was guillotined during the French Revolution—but his scientific legacy endures.
↳ Lavoisier's work laid the foundation for modern chemistry.
One equation, one check.
For any reaction, quickly verify: total mass of reactants = total mass of products. If not, you've missed a product or the equation is unbalanced.
↳ A simple mass balance check catches many errors.
The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. The total mass of reactants equals the total mass of products, forming the foundation for balancing chemical equat…
Full explanation, worked examples & memory tricks in the app
All 17 questions, laddered from warm-up to topper-level, each with its answer and the reasoning behind it.
Q1. Which statement best describes the law of conservation of mass?
BeginnerB · Matter is neither created nor destroyed in a closed system.
The law states that in a closed system, matter is neither created nor destroyed; total mass before equals total mass after.
Q2. In any chemical reaction, the total mass of the reactants is:
BeginnerB · Equal to the total mass of the products
Because atoms are rearranged and not lost or gained, the mass of reactants equals the mass of products.
Q3. During a chemical reaction, atoms of the reactants are:
BeginnerB · Rearranged to form new products
Atoms are simply rearranged during a reaction; none are created or destroyed.
Q4. Which change is an example of conservation of mass in a physical change?
BeginnerC · Ice melting into water with the same mass
Melting is a physical change; the water molecules are simply rearranged, so the mass of ice equals the mass of melted water.
Q5. Which scientist is credited with establishing the law of conservation of mass?
BeginnerB · Antoine Lavoisier
Lavoisier's experiments in the late 18th century provided early strong evidence for the law.
Q6. Antoine Lavoisier is credited with establishing the law of conservation of mass in the late 18th century.
BeginnerA · True
Antoine Lavoisier is credited with establishing the law of conservation of mass in the late 18th century.
Q7. A student burns a candle inside a sealed jar and weighs it before and after. What is observed?
IntermediateD · The mass stays the same because all products remain inside
In a sealed container, gases such as carbon dioxide and water vapour remain trapped, so total mass is conserved.
Q8. Vinegar and baking soda react in an open flask, and the mass appears to decrease. What is the most likely reason?
IntermediateA · Carbon dioxide gas escaped from the flask
In an open system, escaping carbon dioxide carries mass away, causing an apparent mass loss.
Q9. Why must chemical equations be balanced?
IntermediateB · To show that the number of each type of atom is equal on both sides
Balancing reflects the conservation of atoms, and therefore mass, in a chemical reaction.
Q10. A learner says 'weight is conserved in a chemical reaction.' What is the correct response?
IntermediateD · It is mass that is conserved; weight depends on gravity
Mass is the amount of matter (kg); weight is a force (N) that depends on gravity. Conservation applies to mass.
Q11. In the reaction $2H_2 + O_2 \rightarrow 2H_2O$, how many oxygen atoms are on each side?
IntermediateC · 2
The left side has $O_2$ (2 oxygen atoms); the right side has $2H_2O$ (2 oxygen atoms). Both sides have 2.
Q12. Which condition is required to verify conservation of mass experimentally?
IntermediateA · The system must be closed so no matter escapes or enters
A closed system prevents matter from entering or leaving, allowing accurate mass comparison.
Q13. Which statement about nuclear reactions and conservation of mass is correct?
AdvancedB · A small amount of mass converts to energy, so mass is not exactly conserved
In nuclear reactions, mass-energy equivalence ($E=mc^2$) means a tiny amount of mass converts to energy; for chemistry, mass conservation is an excellent approximation.
Q14. A sealed flask contains vinegar and baking soda before reaction. After reaction, the total mass is unchanged. Which best explains this?
AdvancedC · All products, including carbon dioxide gas, remain inside the closed flask
In a closed system, gases cannot escape, so the total mass of reactants equals the total mass of products.
Q15. In the combustion of methane $CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$, which atom count is correct on both sides?
AdvancedB · 1 C, 4 H, 4 O
Counting: left has 1 C, 4 H, 4 O; right has 1 C (in $CO_2$), 4 H (in $2H_2O$), and 4 O (2 in $CO_2$ + 2 in $2H_2O$).
Q16. Why is conservation of mass important in industrial chemical production?
AdvancedA · It allows calculation of reactant and product quantities because no mass is lost
Industries use the law to calculate yields and control processes, such as in the Haber process for ammonia.
Q17. A sealed container holds 10 g of reactants that undergo a chemical reaction. After the reaction, the mass of the products is measured to be 8 g. Which of the following statements best explains this discrepancy?
AdvancedA · The reaction produced a gas that escaped the sealed container.
The correct option is that the reaction produced a gas that escaped the sealed container. In a closed system, mass should be conserved, but if gases escape, it can lead to a decrease in measured mass, demonstrating the importance of maintaining a closed system during reactions.
18 flashcards in this kit — the app reviews them with spaced repetition so the right card returns on the right day.
Every game is built from this kit's own content — scores feed your mastery, so playing counts as studying.
Word Match
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True False
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Memory Match
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Flashcard Battle
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Speed Quiz
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Guess Term
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Sequence Builder
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Categorization
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Revision Battle
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