Catalysts lower the Activation Energy by providing alternative routes
The over all energy change for the reaction (triangle H) remains the same.
Energy must always be supplied to break bonds
During reactions - old bonds are broken, new formed
Energy must be supplied to break existing bonds - endothermic
Energy is released when new bonds are formed - exothermic
Every bond has a particular bond energy for it, it varies depending on the compound the bond occurs in
These can calculate the overall energy change for a reaction
Example - the formation of HCL
H-H: +436kJ; Cl-Cl: +242kJ; H-Cl: +431kJ
The energy required to break original bonds is 436+242 = +678kJ
Energy released by forming new bonds is 2 x 431 = +862kJ
More energy is released than it is used to form product: 862 - 678 = 184kJ released
It is a exothermic reaction - TriangleH = -184kJ
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