Enthalpy and Entropy Lesson # 10

There are two factors that determine the direction that reactions proceed in. These two factors will also allow you to predict the relative amount of reactants and products at equilibrium. 1.Reactions tend to proceed toward minimum enthalpy. Enthalpy is PE. Reactions tend to go downhill in enthalpy. Exothermic ΔH is –ve Downhill Products Favoured

1.Reactions tend to proceed toward minimum enthalpy. Enthalpy is PE. Reactions tend to go downhill in enthalpy. Endothermic ΔH is +ve Uphill Reactions Favoured

2.Reactions tend to go toward maximum entropy. Watch Simulation Entropy is randomness or a measure of how spread out, shuffled up, or broken up the system is. Less EntropyMore Entropy H 2 O (s) H 2 O (l) H 2 O (l) H 2 O (g) NaCl (s) NaCl (aq) N 2 O 4(g) 2NO 2(g) glassbroken glass clean roommessy room

Based on Enthalpy and Entropy describe each reaction. 1.Zn (s) + 2HCl (aq) → H 2(g) + ZnCl 2(aq) ΔH = -252 KJ For entropy- only look at phase symbols- mainly gases 0 gases1 gas max entropy- favours products! For enthalpy draw the PE diagram! The low side is favoured by enthalpy- products. Favours the Products. Big Keq High Yield Goes to Completion

Based on Enthalpy and Entropy describe each reaction. 2.N 2 O 4(g) →2NO 2(g) ΔH = +20 KJ 1 gases2 gases Phase Symbols- max entropy favours products! Goes to equilibrium. Keq is about 1 PE Diagram- minimum enthalpy favours reactants

Based on Enthalpy and Entropy describe each reaction. 3.3C (s) +3H 2(g) + 45 KJ→ C 3 H 6(g) 3 gases1 gas Phase Symbols- max entropy favours reactants! Favours the reactants. Little Keq Low Yield Does not occur PE Diagram- minimum enthalpy favours reactants

4. Here is an easy way to analysis a reaction. √max entropy√min enthalpy ⇌

4. Here is an easy way to analysis a reaction. √max entropy√min enthalpy √ ⇌ ⇌

4. Here is an easy way to analysis a reaction. √max entropy√min enthalpy √ ⇌ √ ⇌

4. Here is an easy way to analysis a reaction. √max entropy√min enthalpy √ ⇌ √ equlibrium ⇌

4. Here is an easy way to analysis a reaction. √max entropy√min enthalpy √ ⇌ √ equlibrium ⇌ √ ⇌

4. Here is an easy way to analysis a reaction. √max entropy√min enthalpy √ ⇌ √ equlibrium ⇌ √ √ ⇌

4. Here is an easy way to analysis a reaction. √max entropy√min enthalpy √ ⇌ √ equlibrium ⇌ √ √ products favoured ⇌

4. Here is an easy way to analysis a reaction. √max entropy√min enthalpy √ ⇌ √ equlibrium ⇌ √ √ products favoured √ ⇌ ⇌

4. Here is an easy way to analysis a reaction. √max entropy√min enthalpy √ ⇌ √ equlibrium ⇌ √ √ products favoured √ √ ⇌ ⇌

4. Here is an easy way to analysis a reaction. √max entropy√min enthalpy √ ⇌ √ equlibrium ⇌ √ √ products favoured √ √ ⇌ reactants favoured ⇌

4. Here is an easy way to analysis a reaction. √max entropy√min enthalpy √ ⇌ √ equlibrium ⇌ √ √ products favoured √ √ ⇌ reactants favoured √ ⇌ ⇌

4. Here is an easy way to analysis a reaction. √max entropy√min enthalpy √ ⇌ √ equlibrium ⇌ √ √ products favoured √ √ ⇌ reactants favoured √ ⇌ √ ⇌

4. Here is an easy way to analysis a reaction. √max entropy√min enthalpy √ ⇌ √ equlibrium ⇌ √ √ products favoured √ √ ⇌ reactants favoured √ ⇌ √ equlibrium ⇌

4. Here is an easy way to analysis a reaction. √max entropy√min enthalpy √ ⇌ √ equlibrium ⇌ √ √ products favoured √ √ ⇌ reactants favoured √ ⇌ √ equlibrium ⇌ √ √

4. Here is an easy way to analysis a reaction. √max entropy√min enthalpy √ ⇌ √ equlibrium ⇌ √ √ products favoured √ √ ⇌ reactants favoured √ ⇌ √ equlibrium ⇌ √ √ products favoured

4.Describe the change in entropy for an endothermic equilibrium system. Maximum entropy Must be on the opposite side of min enthalpy to get an equilibrium. Minimum enthalpy Entropy must increase

5.Describe the change in entropy for an exothermic equilibrium system. Minimum enthalpy Maximum entropy Entropy is decreasing Enthalpy is decreasing

Equilibrium is a compromise between the tendencies toward minimum enthalpy and maximum entropy.