Law of conservation of mass

• What is the law of conservation of mass?

  No atoms are lost or made in a chemical reaction; they join together in different ways to form products.
• Why is the number of atoms of each element the same on both sides of a balanced symbol equation?

  Because atoms are not lost or made in a chemical reaction.
• What does the total mass of the products equal in a chemical reaction?

  The total mass of the products is equal to the total mass of the reactants.
• How is the sum of the relative formula masses of the reactants related to the products?

  The sum of the relative formula masses of the reactants is equal to the sum of the relative formula masses of the products.
• How can the mass of one substance in a reaction be calculated?

  • If the masses of the other substances are known, the mass can be calculated.
  • Example:
  • Calcium carbonate is made up of 28 grams of calcium oxide and 22 grams of carbon dioxide.
  • Total mass = 28 g + 22 g = 50 g of calcium carbonate.
• What happens to the total mass in a closed system during a chemical reaction?

  The total mass remains the same during the reaction.
• What is a closed system in chemistry?

  A closed system is one in which no substances can enter or leave during a reaction.
• What is an example of a closed system reaction?

  An acid-alkali neutralisation reaction in a stoppered flask.
• What occurs in a non-enclosed system during a chemical reaction?

  Substances can enter or leave the system.
• What is an example of a non-enclosed system?

  An open flask or boiling tube.
• What happens to the total mass when a gas escapes from a non-enclosed system?

  The total mass appears to decrease.
• What happens to the total mass when a gas is gained in a non-enclosed system?

  The total mass appears to increase.
• What is thermal decomposition?

  It is a type of reaction in which a compound breaks down to form two or more substances when heated.
• In the example of heating calcium carbonate, what is the mass of the solid that remained after heating?

  1. 60 g of solid remained after heating.
• Why does the mass appear to have decreased when calcium carbonate is heated?

  The mass appears to have decreased because carbon dioxide escapes to the air.
• What is the total mass of the solid and gas products in the calcium carbonate reaction?

  The total mass of the solid and gas products will be 10.0 g.