ENERGETICS

• Enthalpy, H


  the heat energy content of a reaction, kJmol-1
• Enthalpy change, ΔH


  the amount of heat evolved or absorbed in a reaction carried out at a constant pressure, kJmol-1
• Activation energy

  the minimum energy required to break bonds
• Exothermic

  a reaction where energy is released to surroundings so temperature rises
• Endothermic

  a reaction where energy is absorbed so temperature decreases
• Is forming bonds exothermic or endothermic?

  exothermic
• Is breaking bonds exothermic or endothermic?

  endothermic
• q = m c ΔT
• ΔH = q / n
• What does q stand for?

  energy released or absorbed in reaction
• what is m measured in?

  g
• what does c stand for?

  specific heat capacity/ constant
• what does ΔT stand for?

  Change in temperature
• We assume that the density of all aqueous solutions is 1gcm-3 (same as water) so 1cm3 = 1g
• q in the equation for specific heat capacity is measured in J

  q in the equation for enthalpy change is measured in kJ
• Mean bond enthalpies


  energy needed to break 1 mole of a covalent bond in gaseous state averaged over different molecules
• CO and N2 both have triple bonds
• Enthalpy of formation

  The energy change when one mole of a substance is formed from its constituent elements with all substances in their standard states and conditions.