1. Aims of lesson: To investigate the effect of catalysts on activation energy and enthalpy change.

2. Starter 1. Calculate the mass in grams of each of the following: a.5 moles of water b. 0.1 moles of copper c.3 moles of sodium chloride d.10 moles of oxygen

3. Energy Changes and Catalysts

4. The energy profile for an exothermic rxn where a reactant R changes into product P is shown: A catalyst weakens the bonds and allows the reaction to occur at a lower temperature. R P Ea without catalyst Ea with catalyst

5. Thus a catalyst lowers the activation energy (Ea) required to start the reaction. N.B. A catalyst DOES NOT affect the ENATHALPY CHANGE (ΔH)

6. Reversible Reactions e.g. formation of ammonia in the Haber process (uses iron as a catalyst) N 2 + 3H 2  2NH 3 R P N 2 + H 2 NH 3 -50kJ Ea for the FORWARD rxn Ea for the REVERSE rxn

7. ΔH (forward) = -50kJ mol -1 EXOTHERMIC ΔH (reverse) = +50kJ mol -1 ENDOTHERMIC i.e. for reversible reactions the value of ΔH is the SAME for both directions but the SIGN changes for each direction.