11Reversable Reactions and Keq aA + bB cC + dDKeq = equilibrium constantKeq = [productC]c[productD]d [reactantA]a[reactantB]bKeq changes only when the temperature changes.
12Reversible reactions reach a state of dynamic equilibrium N2 + 3H2 2 NH3Keq = [NH 3]2[H2]3 [ N2]
13LeChatelier’s principle A system at equilibrium resists change. If it is exposed to stress (change) it will shift the equilibrium point to try to reduce the stress (change)[Co(H2O)6]+2 + 4Cl- <==> [CoCl4]-2 + 6H2OPink blue
14LeChatelier’s principle If you add a reactant – the equilibrium shifts toward the productIf you add a product – the equilibrium shifts toward the reactantIf you take away a reactant – the equilibrium shifts toward the reactantsIf you take away a product – the equilibrium shifts toward the product side
15LeChatelier’s principle & heat If the reaction is exothermic (heat is a product), So, adding heat shifts the reaction to the reactant sideIf the reaction is endothermic (heat is a reactant) – adding heat shifts the reaction to the product side
16LeChatelier’s principle & Pressure If the reaction contains gas particles, pressure is considered a “stress” condition2SO2 + O2 2SO3Adding pressure shift the equilibrium to the side with fewer gas particles will have less pressure
17Entropy: chaos The universe favors chaos Parts of a whole DS = Sp-Sr UnmixUnexplodeunmeltDS = Sp-SrIf DS is + , entropy change is favored
18Is the reaction “spontaneous” This is a “tug of war” between entropy and enthalpyDG = DH - T DS (T is in kelvin)If Gibbs free energy is a negative number, the reaction is spontaneousIf Enthalpy is negative, (exothermic), and entropy is + (chaos favored) the reaction is always spontaneousIf one of the conditions is not favored – it becomes a tug of war