Conservation of Mass
The law of conservation of mass says that atoms are neither created nor destroyed in a chemical reaction, so total mass stays the same.
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The law of conservation of mass says that atoms are neither created nor destroyed in a chemical reaction, so total mass stays the same.
- Mass of reactants equals mass of products
- Apparent mass changes come from gases escaping
- Underpins balanced equations
🧠 Quick quiz
Three questions. Score 2 or more to complete the topic.
What is Conservation of Mass?
Within Chemistry, which covers atoms, bonding, reactions, the periodic table, organic chemistry and the chemistry of everyday life, this topic explains Conservation of Mass. Chemistry links what you can see in the lab to the particles and bonds behind it, so each topic here shows that link in a model.
Check that you can explain Conservation of Mass in your own words and give one example from everyday life. If you can do that, you have understood the core idea.
Understanding Conservation of Mass helps you explain why substances behave as they do, from cleaning products and food to medicines.
Conservation of Mass in detail
The law of conservation of mass states that in a chemical reaction the total mass of reactants equals the total mass of products, because atoms are rearranged, not created or destroyed. In a closed system, the mass does not change.
Apparent changes in mass happen when a gas is gained or lost: magnesium burning in air gains mass because it combines with oxygen, and a carbonate losing carbon dioxide appears to lose mass in an open container. Mass-balance calculations rely on this law, and it is the reason equations must be balanced.
How the interactive helps you understand Conservation of Mass
Watch the reaction model in the interactive. Use any sliders or buttons it offers to change the values and see how the reaction model responds.
Before you change anything, predict the result. Then change one value at a time and check whether your prediction was right. This is a quick way to build a correct mental model of Conservation of Mass.
Real-life uses and examples
- Read a chemical equation or diagram and work out what Conservation of Mass shows.
- Explain Conservation of Mass in an exam by linking the particles involved to what you observe.
- Use Conservation of Mass to explain what happens in a lab experiment and why.
Common mistakes to avoid
- Describing what happens without explaining the particles or bonds involved.
- Mixing up the names of substances or ions when you describe Conservation of Mass.
- Learning the definition without testing it. Use the quiz and the interactive to check that you can apply the idea.
Frequently asked questions about Conservation of Mass
What is Conservation of Mass?
The law of conservation of mass says that atoms are neither created nor destroyed in a chemical reaction, so total mass stays the same.
What are the most important points about Conservation of Mass?
The main points are: Mass of reactants equals mass of products; Apparent mass changes come from gases escaping; Underpins balanced equations.
Why is Conservation of Mass useful?
Understanding Conservation of Mass helps you explain why substances behave as they do, from cleaning products and food to medicines.
How can I practise Conservation of Mass?
Open the interactive at the top of this page and change the controls one at a time. Predict the result before each change, then take the three-question quiz. A score of two or more marks the topic as complete on this device.
Which topics are related to Conservation of Mass?
Related topics in Chemistry include Reacting Masses, Molar Volume of Gases, Strong and Weak Acids.