Question

Which of the following is not a characteristics of a chemical change?

• A. It is a permanent change
• B. Exchange of energy take place
• C. No new substance is formed
• D. The change is irreversible

Answer 1

The correct option is C

No new substance is formed

Chemical change: Chemical change is a chemical reaction that is accompanied by a change in the composition of matter.

The explanation for the correct answer

Option C

• In a chemical change atoms in reactants rearrange among themselves to form one or more new products with different characteristics than the reactants.
• Example: Hydrogen(${\mathrm{H}}_2$) and Oxygen(${\mathrm{O}}_2$) combine to form a water molecule(${\mathrm{H}}_2\mathrm{O}$).
• Chemical equation:

$\underset{\mathrm{Hydrogen}}{2{\mathrm{H}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)}$

The explanation for the incorrect answers

Option A

• Chemical changes are permanent.
• Since the original composition of substance changes, one or more new substances are formed in a chemical change.
• Example: Cooking, digestion of food, and burning of wood are permanent chemical changes.

Option B

• The exchange of energy that takes place during the chemical reaction.
• During chemical reaction energy is either supplied or released.
• Chemical reaction that releases energy in the form of heat is called an exothermic reaction.
• Rusting is an example of an exothermic reaction.
• A reaction that absorbs energy from its surroundings in the form of heat is called an endothermic reaction.
• Evaporation of water, baking bread, and frying egg are examples of an endothermic reaction.

Option D

• All the chemical changes are irreversible.
• Once the chemical properties of a substance are changed, it becomes another substance.
• Thus, it cannot return to its original state.
• Example: Baking a cake, cooking an egg, and iron rusting are irreversible chemical changes.

Conclusion: Hence option C is correct.