Enthalpy Changes

Cards (20)

  • Enthalpy
    The heat stored in a chemical system
  • Exothermic (-ΔH)

    A product releases heat into the surroundings, therefore feels hotter
  • Exothermic reaction profile
  • Endothermic (+ΔH)

    A product absorbs heat from its surroundings, therefore feels cooler)
  • Endothermic reaction profile
  • Activation energy
    The energy required to start a chemical reaction
  • Standard conditions
    298K and 100kPa
  • Standard states
    Physical states under standard conditions
  • Enthalpy change of reaction
    The enthalpy change when the reaction occurs in the molar quantities shown in the chemical equation under standard conditions
  • Enthalpy change of formation
    The energy required to form one mole of a gaseous compound is formed from its elements under standard conditions
  • Enthalpy change of combustion
    The energy required to completely burn one mole of a gaseous compound under standard conditions
  • Enthalpy change of neutralisation
    The energy change of a reaction of an acid and a base associated with the formation of 1 mole of water, it is measured per mole of water produced
  • Equation to measure enthalpy change
    Equation to measure enthalpy change
    Q=MCΔT where
    Q= Heat energy (J)
    M= Mass of solution (g)
    c = Specific heat capacity
    ΔT = Change in temp (K)
  • Average bond enthalpy
    The breaking of 1 mole of bonds in gaseous molecules
  • Making bonds is
    Exothermic
  • Breaking bonds is
    Endothermic
  • Hess cycle

    -An alternative route is used
    -Products and reactants are the same
    -Energy of initial reaction is equal to energy of alternative route reaction
  • Why can't enthalpy of formation be calculated directly?
    The reaction may produce multiple compounds
  • Which direction are the arrows pointing in a hess cycle of formation?
    Up (forming the products)
  • Which direction are the arrows pointing in a hess cycle of combustion?
    Down