Question

Which of the following statements is true?
A. The total mass of the system remains same in a chemical change
B. A chemical change is permanent and irreversible
C. A physical change is temporary and reversible
D. All of the above

Answer 1

Hint: By principle of conservation of mass, the total mass before and after reaction does not change. But the phases of the molecules may change based on the conditions. The shape, phase, size of the individual materials of the reaction may change but can be reversed back if the conditions change. But once the reaction is done, the products cannot be turned to reactant again.

Complete step by step solution:
A chemical reaction takes place where reactants completely convert into products. Altogether new sets of molecules are created out of the molecules in the reactants. But by principle of conservation of mass the total mass of the reactants remains the same as the mass of the products after the chemical reaction. Thus options A and B are correct. A physical change involves change in the shape, size, form the material in which the reactants and products are in. Even the phase change of the material comes under the umbrella of physical changes. Physical changes means that there is no change in the molecular structure of the material but the matter can be in any form based on the conditions. These changes are reversible. Therefore, we can say that option D is the correct answer.

Note: When we say chemical changes are irreversible it is because once the products are created out of reactants then it requires another set of chemical reactions to bring back the original products. Whereas in physical changes, the melting, mixing of material can be reversible without changing the individual chemical composition.