Chapter 3

• What does the law of conservation of mass state?

  No atoms can be created or destroyed
• What does the law of conservation of mass imply about reactants and products?

  Their masses must be exactly the same
• How do we balance symbol equations?

  By ensuring mass of reactants equals products
• What do small subscript numbers in chemical formulae indicate?

  Number of atoms in a molecule
• What does the large number in front of a molecular formula represent?

  Number of molecules in the reaction
• What does 'mr' stand for in chemistry?

  Relative formula mass
• How do you calculate relative formula mass?

  Add individual atomic masses of atoms
• How do you calculate the percentage by mass of an element in a compound?

  Mass of element divided by total mass
• Why might a reaction appear to change mass when a gas is involved?

  Gases may escape or enter the system
• What happens to the balance reading when a metal burns in oxygen?

  The reading increases due to oxygen mass
• What occurs during the thermal decomposition of a metal carbonate?

  It produces metal oxide and carbon dioxide
• What is uncertainty in scientific measurements?

  Range of possible values around a reading
• How do you calculate percentage uncertainty?

  Range of values divided by mean value
• What is the chemical symbol for moles?

  mole
• What is Avogadro's number?

  $6.02 \times 10^{23}$
• How many molecules are in one mole of any substance?

  Exactly one mole of molecules
• What is a limiting reactant?

  The reactant that limits product formation
• What is a solution in chemistry?

  Mixture of solute in a solvent
• How do you calculate the concentration of a solution?

  Amount of solute divided by volume of solvent
• What is the standard unit for measuring concentration?

  Grams per decimeter cubed
• How does concentration change with solute mass or solvent volume?

  Higher mass or lower volume increases concentration
• What are the standard conditions for room temperature and pressure?

  20°C and 1 atmospheric pressure
• What volume does one mole of gas occupy at standard conditions?

  24 dm³
• What are the implications of the law of conservation of mass in chemical reactions?

  • Mass of reactants equals mass of products
  • No atoms are lost or gained
  • Essential for balancing equations
• What factors affect the concentration of a solution?

  • Mass of solute
  • Volume of solvent
  • Relationship: Higher mass or lower volume increases concentration