Mass and the Mole

• What state of matter has particles that are far apart?

  Gas
• How do gas particles move?

  Quickly in all directions
• What is the relative formula mass (M) calculated from?

  Sum of all relative atomic masses
• What does the percentage mass of an element in a compound represent?

  Mass of element divided by M_r of compound
• What is a balanced equation?

  Same number of atoms on both sides
• What does the equation 2Mg + O₂ → 2MgO illustrate?

  Balanced equation with 2 magnesium and 2 oxygen
• What is conserved in a chemical reaction?

  Mass of reactants and products
• What is one mole equal to?

  6.02 × 10²³ particles
• What types of particles can be counted as one mole?

  Atoms, molecules, ions, or electrons
• How is the mass in grams of one mole of atoms determined?

  It equals the A_r of the element
• How is the mass in grams of one mole of molecules calculated?

  It equals the M_r of the compound
• How do you calculate the number of moles?

  Number of moles = mass in g / M_r
• What happens to mass in an unsealed reaction vessel during a reaction?

  Mass can change due to gas escape
• What causes a decrease in mass during a reaction?

  A gas escapes the reaction vessel
• What causes an increase in mass during a reaction?

  A gas from the air is a reactant
• What gas is produced in the thermal decomposition of calcium carbonate?

  CO₂ gas
• What happens when magnesium reacts with O₂ gas?

  It produces a solid
• What are the key concepts of quantitative chemistry?

  • Relative Formula Mass (M)
  • Balanced Equations
  • Conservation of Mass
  • The Mole and Avogadro's constant
  • Calculating moles from mass
• What are the implications of mass changes in chemical reactions?

  • Decrease in mass: gas escapes
  • Increase in mass: gas enters
  • Mass is conserved overall