chemistry

• mass

  Quantity of matter in an object
• molar mass

  Mass of one mole of a substance
• relative atomic mass or relative molecular / formula mass

  Ratio of the average mass of the atoms in a sample of an element to the mass of one atom of carbon-12
• molar gas volume, taken as 24 dm3 at room temperature and pressure, r.t.p.

  The volume occupied by one mole of any gas at room temperature and pressure
• Electrolysis

  The decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current
• Anode

  The positive electrode in an electrolytic cell
• Cathode

  The negative electrode in an electrolytic cell
• Electrolyte

  The molten or aqueous substance that undergoes electrolysis
• Describe the transfer of charge during electrolysis

  1. Movement of electrons in the external circuit

  2. Loss or gain of electrons at the electrodes

  3. Movement of ions in the electrolyte
• Products formed during electrolysis of

  • Molten lead(II) bromide
  • Concentrated aqueous sodium chloride
  • Dilute sulfuric acid
• Metals or hydrogen are formed at the cathode and non-metals (other than hydrogen) are formed at the anode
• Metal objects are electroplated to improve their appearance and resistance to corrosion
• Products formed during electrolysis of aqueous copper(II) sulfate

  • Using inert carbon/graphite electrodes
  • Using copper electrodes
• Hydrogen-oxygen fuel cell

  Uses hydrogen and oxygen to produce electricity with water as the only chemical product
• Hydrogen-oxygen fuel cells

  • Advantages and disadvantages compared to gasoline/petrol engines in vehicles
• Exothermic reaction

  Transfers thermal energy to the surroundings leading to an increase in the temperature of the surroundings
• Endothermic reaction

  Takes in thermal energy from the surroundings leading to a decrease in the temperature of the surroundings
• Reaction pathway diagrams can show exothermic and endothermic reactions
• Enthalpy change, ∆H

  The transfer of thermal energy during a reaction. ∆H is negative for exothermic reactions and positive for endothermic reactions
• Activation energy, Ea

  The minimum energy that colliding particles must have to react
• Draw and label reaction pathway diagrams for exothermic and endothermic reactions

  1. Reactants

  2. Products

  3. Enthalpy change of the reaction, ∆H

  4. Activation energy, Ea
• Bond breaking is an endothermic process and bond making is an exothermic process
• Physical change

  A change in the physical properties of a substance without any change in its chemical composition
• Chemical change

  A change that results in the formation of one or more new substances with different properties
• Changing the concentration of solutions

  Affects the rate of reaction
• Changing the pressure of gases

  Affects the rate of reaction
• Changing the surface area of solids

  Affects the rate of reaction
• Changing the temperature

  Affects the rate of reaction
• Adding or removing a catalyst, including enzymes

  Affects the rate of reaction
• A catalyst increases the rate of a reaction and is unchanged at the end of a reaction
• Describe practical methods for investigating the rate of a reaction

  1. Change in mass of a reactant or a product

  2. Formation of a gas
• Collision theory

  • Number of particles per unit volume
  • Frequency of collisions between particles
  • Kinetic energy of particles
  • Activation energy, Ea
• Changing the concentration of solutions

  Affects the rate of reaction (using collision theory)
• A catalyst decreases the activation energy, Ea, of a reaction
• Reversible reaction

  A chemical reaction that can proceed in both the forward and reverse directions
• Describe how changing the conditions can change the direction of a reversible reaction

  1. Effect of heat on hydrated compounds

  2. Addition of water to anhydrous compounds
• Equilibrium

  In a closed system, when the rate of the forward reaction is equal to the rate of the reverse reaction and the concentrations of reactants and products are no longer changing
• Predict and explain how the position of equilibrium is affected by

  1. Changing temperature

  2. Changing pressure

  3. Changing concentration

  4. Using a catalyst
• Symbol equation for the production of ammonia in the Haber process: N2(g) + 3H2(g) ⇌ 2NH3(g)
• Sources of hydrogen (methane) and nitrogen (air) in the Haber process