conservation of mass

• CONSERVATION OF MASS:


  • No atoms are CREATED or DESTROYED in a chemical reaction.
  • Meaning the mass of the reactants EQUALS the mass of the products.
  • A balanced chemical equation obeys this law, showing the same number & types of atoms on both sides.
• For the reaction 2Ca + O2 → 2CaO

  • There're 2 calcium atoms & 2 oxygen atoms before & after the reaction, showing that mass is conserved.
• • If mass INCREASES, it could be due to a gas from the air becoming part of the product in an unsealed container.
  • If mass DECREASES, a gas may have formed & ESCAPED from the reaction mixture in a non-enclosed system.
• When Sodium reacts with Oxygen:

  The mass of the Sodium appears to increase.

  • Because the Oxygen in the air COMBINES with the Sodium to form Sodium Oxide.
  • The Oxygen’s mass can not be measured as it is a gas, but after it combines, it's a part of the solid so it CAN be weighed.

  
• When Calcium Carbonate is heated in a THERMAL decomposition reaction:

  It releases Carbon Dioxide GAS which escapes.

  • Meaning it can’t be weighed.
  • So when you weigh the products, the mass appears to decrease as the mass of the Carbon Dioxide is not measured once it escapes.