Conservation of Mass

• What is one of the most important concepts in chemistry?

  The idea of conservation of mass
• What does the conservation of mass mean in a chemical reaction?


  Mass is always conserved; no atoms are created or destroyed
• In the reaction of sodium and chlorine, how many sodium chlorides are formed if there are two chlorine atoms?


  Two sodium chlorides
• What principle is used every time you balance a chemical equation?


  The principle of conservation of mass
• How do you compare the total relative formula masses of each side in a chemical reaction?


  By calculating the sum of the masses of the reactants and products
• What is the total relative formula mass on the left side of the sodium and chlorine reaction?


  117
• If 2.3 grams of sodium reacts with 3.5 grams of chlorine gas, what is the mass of sodium chloride produced?


  1. 8 grams
• What happens to the mass during a chemical reaction when using a set of scales?


  The mass should stay the same throughout the entire reaction
• What is an important exception to the conservation of mass rule?


  The mass might seem to change if a gas is involved
• What happens when magnesium reacts with oxygen to form magnesium oxide?


  The relative formula mass of magnesium oxide is higher than that of magnesium
• If one gram of magnesium forms how much magnesium oxide?


  About 1.6 grams
• Why might the weight of products seem to have decreased when decomposing calcium carbonate?


  Because the gaseous CO2 would float off into the air
• What happens to the mass if the experiment is conducted in a sealed container?

  The mass would stay the same because all gases would be trapped
• What is the conservation of mass principle in chemical reactions?


  • Mass is always conserved in a chemical reaction
  • No atoms are created or destroyed
  • Changes occur only in the bonds between atoms
• What should you do to avoid mass measurement issues in reactions involving gases?

  • Conduct experiments in a sealed container
  • This ensures all reactants and products are accounted for
• What are the implications of conducting a reaction in an open vs. sealed container?

  • Open container: gas may escape, leading to apparent mass loss
  • Sealed container: all reactants and products are measured, mass remains constant
• What happens to the mass of reactants and products when a gas is involved?


  • Mass may appear to increase if a gas is a reactant
  • Mass may appear to decrease if a gas is a product