The Law of Conservation of Mass
The Law of Conservation of Mass
- The Law of Conservation of Mass states that no matter is lost or gained during a chemical reaction.
- Mass is always conserved, therefore the total mass of the reactants is equal to the total mass of the products, which is why all chemical equations must be balanced
- The sum of the relative atomic/molecular masses of the reactants will be the same as the sum of the relative atomic/ molecular masses of the products, taking into account the stoichiometry (balancing)
- Changes of state do not affect the conservation of mass, but can appear to do so if gaseous products are allowed to escape
- If the reaction flask is closed and no other substance can enter or leave the system, then the total mass of the reaction flask will remain constant
- This can be demonstrated using many reactions including precipitation reactions, in which two solutions react to form an insoluble solid called a precipitate
- For example, the reaction between calcium chloride and sodium sulfate produces a precipitate of calcium sulfate.
- If carried out in a closed system then the mass before and after the reaction will be the same
- The balanced equation is:
- This can be demonstrated using many reactions including precipitation reactions, in which two solutions react to form an insoluble solid called a precipitate
CaCl2 (aq) + Na2SO4 (aq) ⟶ CaSO4 (s) + 2NaCl (aq)
Diagram showing the conservation of mass in a precipitation reaction