Conservation of Mass
- Mass cannot be created or destroyed, but it can be rearranged
- The Law of conservation of mass states the mass must state the same over time
- During chemical processes, the atoms in chemical compounds are rearranged to form new ones
- The principle of mass conservation can be used to calculate the amount of products or the amount of reactants for a given chemical equation
Worked example
The following chemical reaction is carried in a chemical reactor:
2H2 + O2 → 2H2O
If 4 g of hydrogen gas were used during the reaction, and 36 g of water were collected at the end of the reaction. How much oxygen gas reacted?
Answer:
- Step 1: Count the amount of grams of reactants and products. If there is an unknown mass, place it as an unknown (x)
|
Mass of the reactants (g) |
Mass of the products (g) |
|
4 + x |
36 |
- Step 2: Set up a mathematical equation using the law of conservation of mass
mass of reactants = mass of products
4 + x = 36
- Step 3: Solve the equation to find the unknown mass of oxygen
4 + x = 36
x = 36-4 =32
- 32 g of O2 reacted
