Understanding

System vs Surroundings System: the reactants ALONE e.g. NaOH and HCl Surroundings: everything else, e.g. beaker, water, thermometer, cup

  • surroundings is not directly involved in the chemical reaction while the system is

Energy Changes

Energy Changes

Reactions

Exothermic and Endothermic Reactions


Enthalpy Change

Enthalpy Change


Energy Level Diagrams

Energy Level Diagrams


Energy Profile Diagrams

Energy Profile Diagrams


Mole + Stoichiometry in Energetics

Mole + Stoichiometry in Energetics


Combustion of Fuels

Combustion of Fuels


Fuel Cells

Fuel Cells


Answer Techniques

Explaining Why Reaction is Endo/Exo

  1. State that bond breaking is endo and bond making is exo
  2. State energy of products higher/lower than reactants
  3. State whether energy taken in from surr to system for breaking bonds in xx mol of xxx compound is more/less than energy released from system to surr. to make new bonds to form xxx mol of xxx compound
  4. Net energy transfer from system to surr / surr to system
  5. Positive/Negative enthalpy change.
  6. Thus Endo/Exo

Important

important to state direction of energy movement ; taken in or given out