Enthalpy

• What is enthalpy?(H)

  A measure of heat energy in a chemical system
• What is a System?

  It is the atoms ions or molecules making up the chemicala
• What is enthalpy change?

  It is the enthalpy of the products - the enthalpy of the reactants
• What is the conservation of energy?

  It is the theory that energy can not be created or destroyed but it can be transferred between the system and surrounding
• Is a reaction exothermic if heat is taken in from the surroundings?

  No it is endothermic
• If the delta H is negative is it exothermic or endothermic?

  Exothermic
• If delta H is positive is it exothermic or endothermic?

  endothermic
• What are the x and y axis on a reaction profile?

  X is progress of the reaction Y is enthalpy of the reaction
• What is the activation energy?

  It is the minimum energy required for a reaction to occur, often shown as Ea
• What are the standard enthalpy conditions?

  100kPa 298K 1moldm-3
• What is the standard enthalpy change of reaction ?

  The enthalpy change that accompanies a reaction in molar quantities, with everything in their standard states
• What is the standard enthalpy of formation?

  enthalpy of the reaction when one mole of a compound is formed in standard conditions
• What is the enthalpy change of combustion?

  It is the enthalpy change where one mole of reactant reacts with oxygen to combust completely.
• What is the enthalpy change of neutrilisation?


  it is the standard energy change that accompanies the acid+base reaction to form one mole of water
• What is the formula for the standard enthalpy change?

  Q=Mc(delta)T

  this will then give you the thermal energy which needs to be /1000 for KJ

  then calculate Mr and moles

  then do Q/moles
• What does it mean if delta H is negative?

  Exothermic reaction.
• What does it mean if Delta H is positive?

  It is an Endothermic reaction
• What is an average bond enthalpy?

  It is the energy required to break one mole of a specified bond into a gaseous molecule
• What is Hess's law?

  It is that the total enthalpy change is independent to the route taken by the reaction
• Hess's cycle-formation

  Reactants -->Products

  \ /

  constituent elements
• Hess's cycle-combustion

  Reactants/elements --> Products

  \ /

  COMBUSTION PRODUCTS
• Suggest whether the enthalpy change of vaporisation of bromine is exothermic or endothermic?

  Endothermic, Energy required to overcome induced dipole–dipole forces
• Explain, in terms of bond breaking and bond forming, why a reaction can be exothermic?

  More energy is released by forming bonds than energy required when breaking bonds