WALKTHROUGH
LAW OF CONSERVATION OF MASS
After a chemical reaction is complete, the mass of the new substance will equal the
mass of the original substance.
Pages
6
Inquiry points
Suggested time
3
15 min
1
Explore the change in mass of mercury
heated in air.
Answers
D
D
T
T
1IP
•
•
•
•
Mass: 2.00
Mass (bell jar + element): 642.00
Final mass after heating: 642.00
Remove the bell jar to find the
mass of the product: 2.16
Talking point!
The law of conservation of mass works on a large scale, and is a good rule to
use in keeping track of particles in chemical reactions. It isn’t perfect, however.
The German physicist Albert Einstein was famous for the equation E = mc2, which
describes a relationship between mass and energy. In fact, it shows they are
interchangable. Adding energy also adds mass to an object. Removing energy
removes mass.
The c stands for the speed of light, which is a pretty big number. The fact it’s
squared makes it much bigger. So energy is equal to mass multiplied by a really,
really big number. Adding or removing energy from chemicals in a chemical
reaction won’t make a significant difference to the product’s mass, but on a tiny
level the mass of the reactants isn’t exactly the same as the mass of the product.
ACTIVITY: LAW OF CONSERVATION OF MASS
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WALKTHROUGH
2
Explore this
T...
Consider why the mass increased.
Read about the chemist Antoine
Lavoisier.
Answers
• greater than
T...
1IP
• The product includes the mass
of oxygen.
• equal to
3
Consider how chemical reactions are
balanced at a molecular level.
Answers
1IP
ACTIVITY: LAW OF CONSERVATION OF MASS
• Add mercury x 2
• Add oxygen x 1
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intoscience.com