Energetics

• What are standard conditions?

  100kpa and 298K
• What is enthalpy change?

  Heat energy transferred in a reaction at constant pressure. Kj/mol-1. Break - make.
• What is an exothermic reaction?

  Gives out energy to surroundings, so temperature in reaction goes up. Products end up with less energy than reactants, so enthalpy change is negative.
• Exothermic reaction examples:

  Combustion, respiration, neutralisation, displacement and oxidation.
• Endothermic reaction examples:

  Photosynthesis, electrolysis and thermal decomposition.
• What is an endothermic reaction?

  Take in energy from surroundings, so temperature in reaction falls. Products have more energy than reactants, so enthalpy change is positive.
• What is mean bond enthalpy?

  Average energy required to break a certain type of bond (covalent) over a range of compounds.
• What is the standard enthalpy change of formation?

  Enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions.
• What is the standard enthalpy change of reaction?

  Enthalpy change when a reaction occurs in the molar quantities shown in the chemical equation, under standard conditions with all reactants & products in their standard states.
• What is the standard enthalpy change of combustion?

  Enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions, with all reactants & products in their standard states.
• State 'Hess's law'

  Total enthalpy change of a chemical reaction is independent of the route taken.
• Bond enthalpy


  Energy required to break a bond. Specific values that differ depending on which atoms are attached to either side of the bond.
• What are the issues with combustion reactions?

  Heat can be lost to surroundings, incomplete combustion (less energy given out) and flammable liquids volatile (may lose fuel to evaporation).
• Enthalpy change equation:

  q=mcat
• Enthalpy of neutralisation:

  Energy change when 1 mole of water is formed by reaction of an acid with an alkali.