Reactions and moles - Higher

• What is the mole in chemistry?

  The mole is the unit for amount of substance.
• How can the number of particles in a substance be found?

  Using the Avogadro constant.
• What does the mass of a product depend on in a chemical reaction?

  It depends upon the mass of the limiting reactant.
• What are reactants in a chemical reaction?

  • Substances present at the start of a chemical reaction.
  • They are consumed during the reaction to form products.
• What is a limiting reactant?

  The limiting reactant is the reactant that is completely used up in a chemical reaction.
• What does it mean if a substance is in excess in a chemical reaction?

  A substance is in excess if there is more than enough of it to react with another reactant.
• How is mass defined in chemistry?

  Mass is the amount of matter an object contains.
• What is a product in a chemical reaction?

  A product is a substance formed in a chemical reaction.
• How does the mass of product formed relate to the limiting reactant?

  The mass of product formed depends upon the mass of the limiting reactant.
• What is the formula to calculate the maximum mass of product formed in a reaction?

  • Use the balanced equation.
  • Use the mass of the limiting reactant.
  • Use the relative atomic mass (A_r) or relative formula mass (M_r) values.
• How do you calculate the amount of magnesium in 12 g?

  Amount of magnesium = \(\frac{12}{24} = 0.5 \text{ mol}\)
• How much hydrogen can be produced from 0.5 mol of magnesium?

  0.5 mol of magnesium produces 0.5 mol of hydrogen.
• What is the mass of hydrogen produced from 0.5 mol?

  Mass of H₂ = M_r × amount = \(2 \times 0.5 = 1 \text{ g}\)
• How do you calculate the maximum mass of carbon dioxide from 1.0 g of calcium carbonate?

  Mass of CO₂ = M_r × amount = \(44 \times 0.01 = 0.44 \text{ g}\)
• What are the steps to deduce a balanced equation from experimental masses?

  1. Write the formulae of the substances.
  2. Calculate the amounts of each substance.
  3. Divide both by the smaller amount to find the ratio.
  4. Write the balanced equation.
• What is the balanced equation for the reaction of magnesium and oxygen?

  2Mg + O₂ → 2MgO
• What is the relative atomic mass (A_r)?

  A_r is the mean relative mass of the atoms of the different isotopes in an element.
• What is the relative formula mass (M_r)?

  M_r is the sum of the relative atomic masses of the atoms in a chemical formula.
• How can balancing numbers in a chemical equation be determined?

  By using masses found by experiment.
• What is the purpose of a balanced chemical equation?

  It ensures the number of units of each element is the same on both sides of the arrow.
• What is the significance of the limiting reactant in a chemical reaction?

  The limiting reactant determines how much product is made.
• What happens when the limiting reactant is all used up?

  The reaction finishes because there is nothing left to react with.
• What is the role of excess reactants in a chemical reaction?

  Excess reactants are not completely consumed and remain after the reaction.