Presentation on theme: "Enthalpy Changes in Chemical Reactions. Enthalpy Enthalpy (H) The “heat content” of a substance It is the total KE and PE of a substance at constant pressure."— Presentation transcript:
Enthalpy Enthalpy (H) The “heat content” of a substance It is the total KE and PE of a substance at constant pressure KE + PE = constant (enthalpy)
Kinetic & Potential Energy KE: it is the energy of MOTION… ex; atoms and electrons moving within the molecules, or in the entire system (reaction) PE: energy existing due to position and the sum of all attractions/repulsions between particles. PE is directly related to BOND energies.
Bond energy Bond energy is the amount of energy required to break/form a bond between two atoms. Ex:
Enthalpy changes Chemists interested in enthalpy changes ( H ) H = H products- H reactants
KE Distributions Increased Temperature = increased number of molecules that have enough energy to react/cross the activation energy barrier successfully. Yes, collisions would also increase, but only 1% more collisions for every 10C increase in Temp.
Activation Energy The minimum potential energy needed in a collision before a reaction can take place. It can also be defined as the minimum energy colliding particles must have in order to have a “successful” collision.