Conservation of Mass

• Conservation of mass

  In a chemical reaction, mass is always conserved - no atoms are created or destroyed, only the bonds between atoms change
• Balancing a chemical equation

  Ensure the number of atoms of each element is the same on both sides of the equation
• Comparing total relative formula masses of reactants and products

  They are equal, demonstrating conservation of mass
• When a reaction involves a gas, the mass may appear to change because the gas can come from or float off into the air and not be measured
• Heating magnesium and it reacting with oxygen

  The mass of the product (magnesium oxide) is greater than the mass of the reactant (magnesium)
• If the experiment is done in a sealed container, the mass of the reactants and products will balance perfectly because the gaseous reactants and products are trapped
• Decomposing calcium carbonate to calcium oxide and carbon dioxide

  The mass of the products appears decreased because the carbon dioxide gas floats off
• Doing experiments in a sealed container avoids the issue of gases escaping and affecting the apparent mass