Chapter 9

• What is the standard enthalpy change of a reaction?

  The enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions.

  • with all reactants and products in their standard states
• What is the standard enthalpy change of formation?

  The enthalpy change that occurs when 1 mole of a compound is formed from its elements under standard conditions.

  • with all reactants and products in their standard states
• What is the standard enthalpy change of combustion?

  The enthalpy change that occurs when 1 mole of a substance is burned completely in oxygen under standard conditions.

  • with all reactants and products in their standard states
• What is the standard enthalpy change of neutralisation?

  The enthalpy change that accompanies the reaction of an acid by a base to form 1 mole of H2O under standard conditions.

  • with all reactants and products in their standard states
• What are the standard conditions?

  100kPa

  25 C OR 298K

  1 mol dm-3
• What is the standard state?


  The state of a substance under standard conditions
• What is the definition of enthalpy change?

  The heat energy transferred (given out or absorbed) during a chemical reaction or physical process.
• What is Hess' law?


  If a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route.
• What is the enthalpy change of any element?


  Zero
• Equation for enthalpy change of a reaction?

  (total bond enthalpies in reactants) - (total bond enthalpies of products)
• Equation for enthalpy change of formation?

  products - reactants
• Equation for enthalpy change of combustion?


  reactants - products
• Define enthalpy.


  the measure of heat energy present in a chemical system
• Define enthalpy change


  the amount of energyh released/taken in during a chemical reaction
• Exothermic reaction


  Release energy into surroundings

  Enthaply change is negative
• Endothermic reaction


  Takes in enery from surroundings

  Enthalpy change is positive
• Define activation energy


  Ea - the minimum energy required for a reaction to take place: where energy to break bonds = energy barrier