3.4 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, meaning no atoms are created or destroyed
• What changes during a chemical reaction according to the conservation of mass?

  Only the bonds between atoms change
• 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 measured on 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 mass of magnesium oxide is higher than that of magnesium alone
• How much magnesium oxide is formed from one gram of magnesium?

  About 1.6 grams of magnesium oxide
• Why might the weight of products seem to decrease when decomposing calcium carbonate?

  Because the gaseous CO2 may float off into the air
• What is the effect of conducting an experiment in a sealed container regarding gas reactions?

  The mass of reactants and products will balance perfectly
• What are the key points to remember about the conservation of mass in chemical reactions?

  • Mass is always conserved in a chemical reaction.
  • Mass may appear to change if a gas is involved.
  • If mass seems to increase, a gas is likely a reactant.
  • If mass seems to decrease, a gas is likely a product.
  • Conduct experiments in a sealed container to avoid mass loss.