Overview
This lecture explains the law of conservation of mass, illustrating how mass remains constant through physical and chemical changes.
Conservation of Mass: Fundamental Concept
- The law of conservation of mass states that matter cannot be created or destroyed during physical or chemical changes.
- When water boils and turns to steam, the total mass remains unchanged if all vapor is collected.
- Gas may be less dense than liquid, but the mass stays the same because molecules simply move apart, not disappear.
- No individual water molecule is lost or altered during phase changes—only their arrangement and movement changes.
Conservation in Chemical Reactions
- Chemical reactions also obey the law of conservation of mass; all atoms present at the start remain after the reaction.
- Balanced chemical equations reflect equal numbers of each atom type on both sides.
- No atoms are created or destroyed during chemical reactions.
Everyday Examples of Conservation
- Rusting of a copper pipe increases its mass because oxygen from air (which has mass) bonds to the copper.
- Atmospheric gases, although invisible and low-mass, contribute mass when they react with other materials.
- When food is eaten, it is broken down by enzymes; matter from food is converted into new cells, energy, or waste, not lost.
Key Terms & Definitions
- Conservation of Mass — The principle that mass in a closed system remains constant, regardless of physical or chemical changes.
- Phase Change — The transformation of matter from one state (solid, liquid, gas) to another without changing molecular composition.
- Chemical Reaction — A process where substances (reactants) are transformed into new substances (products) with no loss of matter.
Action Items / Next Steps
- Review examples of conservation of mass in textbook readings.
- Practice balancing chemical equations to reinforce understanding of atom conservation.