Conservation of mass

Question

In a sealed classroom model, substances react without measurable loss of matter. How should the combined mass of the resulting substances compare with the combined mass of the starting substances?

1. AIt should be equal.✓ Correct

   Ordinary reactions conserve total mass.

2. BIt should be greater.✗ Incorrect

   A reaction does not create additional total mass.

3. CIt should be smaller.✗ Incorrect

   The stated closed model does not lose matter.

4. DIt cannot be compared.✗ Incorrect

   The masses can be compared under conservation of mass.

Answer

A. It should be equal.

Rationale

For an ordinary chemical reaction, the total mass on each side remains the same. A sealed system retains the material being compared.