Summary Questions

• In a reaction, how does the mass of products compare with the mass of reactants?

  The mass of products equals the mass of reactants.
• Why might the mass of a reaction that occurs in an open vessel appear to decrease?

  Because gases may escape into the atmosphere.
• What is the charge on an ion?

  An ion can have a positive or negative charge.
• What is the change in charge in the reaction of magnesium and oxygen gas to form magnesium oxide?

  The charge changes from 0 to +2 for magnesium and from 0 to -2 for oxygen.
• Write a balanced ionic equation using ion composition?

  Mg²⁺ + O²⁻ → MgO
• What is shown by an ionic equation?

  An ionic equation shows the ions involved in a chemical reaction.
• What type of chemical equation would you use to show how electrons are transferred in a reaction?

  A half-equation is used to show electron transfer.
• What does Avogadro's constant represent?

  Avogadro's constant represents the number of particles in one mole, approximately $6.022 \times 10^{23}$.
• Give the formula that links the number of moles with mass and relative formula mass.

  Number of moles = mass / relative formula mass.
• How can you tell if a limiting reactant limits a reaction?

  If one reactant is completely consumed before the others, it is the limiting reactant.
• What is meant by the limiting reactant from a balanced equation and the masses of reactants present?

  The limiting reactant is the reactant that runs out first, determining the maximum amount of product formed.
• What is the difference between an endothermic and an exothermic reaction?

  An endothermic reaction absorbs energy, while an exothermic reaction releases energy.
• Sketch a reaction profile for an exothermic reaction.

  Exothermic reaction profile shows reactants higher than products with a downward slope.
• Sketch a reaction profile for an endothermic reaction.

  Endothermic reaction profile shows products higher than reactants with an upward slope.
• What is meant by the term activation energy?

  Activation energy is the minimum energy required to start a chemical reaction.
• How is energy released when bonds are broken when they are made?

  Energy is released when bonds are formed and absorbed when bonds are broken.
• How would you calculate the overall energy change in a reaction from the bond energies?

  Overall energy change = energy of bonds broken - energy of bonds formed.
• What is: a) an acid b) a base c) an alkali?

  An acid is a proton donor, a base is a proton acceptor, and an alkali is a soluble base.
• Name two ways that you could measure the pH of a solution.

  Using pH paper or a pH meter.
• What are the reactants and products of a neutralisation reaction?

  The reactants are an acid and a base, and the products are salt and water.
• Sketch a titration curve to show how the pH of a solution of acid changes as a base is added.

  The titration curve shows a sharp increase in pH at the equivalence point.
• Write an equation to show the ionisation of ethanoic acid (CH₃COOH), a weak acid, in solution.

  CH₃COOH ⇌ CH₃COO⁻ + H⁺
• Write a balanced equation for the reaction of hydrochloric acid with aluminium.

  2HCl + 2Al → 2AlCl₃ + 3H₂
• Write a balanced equation to show how copper chloride (CuCl₂) is made from copper oxide (CuO) and hydrochloric acid.

  CuO + 2HCl → CuCl₂ + H₂O
• Outline how you could make lead chloride (PbCl₂) using a precipitation reaction.

  Mix lead nitrate and sodium chloride solutions to form lead chloride precipitate.
• Give the half definitions of: a) oxidation, b) reduction.

  Oxidation is loss of electrons, reduction is gain of electrons.
• What is a redox reaction?

  A redox reaction involves both oxidation and reduction processes.
• When a molten ionic compound decomposes during electrolysis, at which electrode does the metal form?

  The metal forms at the cathode during electrolysis.
• Outline how you would set up an electrochemical cell using copper sulfate solution and inert electrodes.

  Place inert electrodes in copper sulfate solution and connect them to a power source.
• Why do the masses of non-inert electrodes change during electrolysis?

  The masses change due to the gain or loss of ions during the electrolysis process.