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

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Presentation transcript:

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

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

Energy Changes and Catalysts

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

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

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

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.