Conservation of Mass
Also known as: law of conservation of mass
A fundamental law stating that in any chemical reaction, the total mass of all reactants exactly equals the total mass of all products, because atoms are rearranged but never created or destroyed. This law is the foundation of all quantitative chemistry.
💡 Intuition
Matter can't vanish or appear from nothing. What goes in equals what comes out.
Core Idea
Atoms are rearranged into new substances — none are created or destroyed in the process.
Formal View
🔬 Example
🎯 Why It Matters
This law is the foundation of all quantitative chemistry. It is why chemical equations must be balanced, why stoichiometry works for calculating reactant and product amounts, and why mass measurements in the lab can verify reaction completeness.
⚠️ Common Confusion
Mass seems to disappear when gases escape—but it's still conserved.
How to Use Conservation of Mass
When this concept appears in chemistry, it usually controls how you interpret a representation, a quantity, or a change in a system. Students make faster progress when they can explain what conservation of mass tells them before reaching for an equation or memorized phrase.
A strong self-check is to say what conservation of mass does, what it does not do, and which nearby idea it is easiest to confuse with. That kind of explanation makes later calculations, lab reasoning, and compare pages much more reliable.
💭 Hint When Stuck
When solving mass conservation problems, set total mass of reactants equal to total mass of products. First add up the masses of all reactants. Then add up the masses of all known products. Finally, solve for the unknown mass using the equation m_{\text{reactants}} = m_{\text{products}}.
Related Concepts
Prerequisites
Next Steps
How Conservation of Mass Connects to Other Ideas
To understand conservation of mass, you should first be comfortable with chemical reaction. Once you have a solid grasp of conservation of mass, you can move on to balancing equations and stoichiometry.
Go Deeper
Frequently Asked Questions
What is Conservation of Mass in Chemistry?
A fundamental law stating that in any chemical reaction, the total mass of all reactants exactly equals the total mass of all products, because atoms are rearranged but never created or destroyed.
Why is Conservation of Mass important?
This law is the foundation of all quantitative chemistry. It is why chemical equations must be balanced, why stoichiometry works for calculating reactant and product amounts, and why mass measurements in the lab can verify reaction completeness.
What do students usually get wrong about Conservation of Mass?
Mass seems to disappear when gases escape—but it's still conserved.
What should I learn before Conservation of Mass?
Before studying Conservation of Mass, you should understand: chemical reaction.