enthalpy and entropy lesson # 10. there are two factors that determine the direction that reactions...
DESCRIPTION
1.Reactions tend to proceed toward minimum enthalpy. Enthalpy is PE. Reactions tend to go downhill in enthalpy. Endothermic ΔH is +ve Uphill Reactions FavouredTRANSCRIPT
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 Entropy More Entropy
H2O(s) H2O(l)
H2O(l) H2O(g)
NaCl(s) NaCl(aq)
N2O4(g) 2NO2(g)
glass broken glass
clean room messy room
Based on Enthalpy and Entropy describe each reaction. 1. Zn(s) + 2HCl(aq) → H2(g) + ZnCl2(aq) ΔH = -252 KJ
For entropy- only look at phase symbols- mainly gases0 gases 1 gas
max entropy- favours products!
For enthalpy draw the PE diagram!The low side is favoured by enthalpy- products. Favours the Products.
Big KeqHigh YieldGoes to Completion
Based on Enthalpy and Entropy describe each reaction. 2. N2O4(g) → 2NO2(g) ΔH = +20 KJ
1 gases 2 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) + 3H2(g) + 45 KJ → C3H6(g)
3 gases 1 gas
Phase Symbols- max entropy favours reactants!
Favours the reactants.Little KeqLow YieldDoes 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 enthalpyMaximum entropy
Entropy is decreasingEnthalpy is decreasing
Equilibrium is a compromise between the tendencies toward minimum enthalpy and maximum entropy.