Humber Admissions Practice Test

What does the Law of Conservation of Mass state?

1. Mass increases during reactions

2. Mass changes form but is conserved

3. Mass is created during chemical reactions

4. Mass can be destroyed in reactions

The correct answer is: Mass changes form but is conserved

The Law of Conservation of Mass is a fundamental principle in chemistry that states that mass cannot be created or destroyed in a closed system during a chemical reaction. This means that the total mass of reactants before the reaction occurs will be equal to the total mass of products after the reaction has taken place. Although matter can change forms (for example, from solid to liquid) or be rearranged during a chemical reaction, the overall mass remains the same, demonstrating that it is conserved. This principle is key in understanding chemical reactions and balances, as it implies that all atoms present before a reaction must also be accounted for after the reaction has occurred. This concept is crucial for stoichiometry calculations, where one can predict the quantities of reactants needed and products formed based on this conservation. The other choices inaccurately represent the law. For example, the suggestion that mass increases during reactions contradicts this principle, as it suggests the creation of mass. Similarly, the idea that mass can be created or destroyed during reactions undermines the foundational concept of mass conservation that underpins chemical science.