The conservation of mass means that matter cannot be made or destroyed during a chemical reaction. This idea is really important for understanding how things change in our everyday lives.

Key Points:

• Mass Before Reaction: The total mass of the stuff you start with (the reactants) should be the same as the total mass of what you end up with (the products).

• Example: Let's look at burning methane gas. When methane ($CH_4$) burns with oxygen ($O_2$), it creates carbon dioxide ($CO_2$) and water ($H_2O$). The total mass of methane and oxygen before burning equals the mass of carbon dioxide and water after burning.

• Numbers:

  • If you have 1 mole of methane ($16 \text{ g}$) and mix it with $64 \text{ g}$ of oxygen, you get $44 \text{ g}$ of carbon dioxide and $36 \text{ g}$ of water.
  • So, before the reaction, you have a total of $80 \text{ g}$. After the reaction, you still have $80 \text{ g}$. This shows how mass stays the same.

This idea helps us understand how mass is important in keeping things stable and changing in our world.