Q1. [1] medium exam-ready
Assertion (A): A chemical equation must be balanced to be used for stoichiometric calculations.
Reason (R): According to the law of conservation of mass, the total mass of reactants must equal the total mass of products in any chemical reaction.
(A) Both A and R are true and R is the correct explanation of A.
(B) Both A and R are true but R is not the correct explanation of A.
(C) A is true but R is false.
(D) A is false but R is true.
- A Both A and R are true and R is the correct explanation of A.
- B Both A and R are true but R is not the correct explanation of A.
- C A is true but R is false.
- D A is false but R is true.
Generated by claude-sonnet-4-6 · 2026-06-26 00:53 · grounding rag
Model Answer
(A) Both A and R are true and R is the correct explanation of A.
A chemical equation must be balanced because the law of conservation of mass states that total mass of reactants equals total mass of products, ensuring equal number of atoms on both sides.
Source: Chapter 1, Section 1.1.2 Balanced Chemical Equations
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Explanation
- A is true: A balanced equation is essential for stoichiometric calculations so that correct mole ratios are used.
- R is true: The law of conservation of mass is correctly stated.
- R correctly explains A: We balance equations specifically because of this law — atoms (and hence mass) must be conserved. The textbook explicitly states: "the total mass of the elements present in the products has to be equal to the total mass of the elements present in the reactants... Hence, we need to balance a skeletal chemical equation."
- Option (B) would be wrong here because R is not just true but is the direct reason why balancing is necessary.