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Enthalpy and Entropy Lesson # 10. There are two factors that determine the relative amount of reactants and products at equilibrium. Reactions tend to proceed toward minimum enthalpy . Reactions tend to go toward maximum entropy. Enthalpy is PE – In an Exothermic Reaction. - PowerPoint PPT Presentation
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Enthalpy and Entropy
Lesson # 10
There are two factors that determine the relative amount of reactants and products at equilibrium.
1.Reactions tend to proceed toward minimum enthalpy.
2.Reactions tend to go toward maximum entropy
Products are Favoured
Enthalpy is PE – In an Exothermic Reaction
The low side (side with the energy) is always favoured- minimum
A + B = C + energy
Reactants are Favoured
Enthalpy is PE – In an Endothermic Reaction
The low side (side with the energy) is always favoured- minimum
A + energy = B + C
Entropy is randomness or a measure of how spread out, or broken up the system is.
Watch Simulation
Less Entropy More Entropy
H2O(s)
H2O(g)H2O(l)
NaCl(s)NaCl(aq)
N2O4(g) 2NO2(g)
glass broken glass
clean room messy room
H2O(l)
Less entropy (s) (l) (aq) (g) More Entropy
P6O9(g) 3P2O3(g)
√ √
√ √
√ max entropy √ min enthalpy
You can tell the yeild of a reaction with enthalpy and entropy
equlibrium
products favoured
⇌
⇌
If they are both on one side that side is favoured
If they are on different sides it’s an equilibrium
Which Way?
Right or left?
Products are favoured
Large Keq
Are the products or Reactants favoured?0 gases 1 gas
1. Zn(s) + 2HCl(aq) H2(g) + ZnCl2(aq) ΔH = -252 KJ
√ max entropy
√ min enthalpy
Goes to Completion
For entropy- only look at phase symbols- mainly gases
High yield
↔?
+ E
⇌ ProductsReactants
Which Way?
Right or left?Equilibrium
Keq is about 1
Are the Products or Reactants favoured?
1 gas 2 gases
2. N2O4(g) 2NO2(g) ΔH = +20 KJ
√ max entropy
√ min enthalpy
↔?+ E
⇌reactants Products
Reactants are favoured
Keq is small
Are the Products or Reactants favoured?
3. 3C(s) + 3H2(g) + 45 KJ C3H6(g)
√ max entropy
√ min enthalpy
Low yield
Reaction does not occur!
↔?
⇌reactants products
4. Describe the change in entropy and enthalpy for an endothermic equilibrium system.
Maximum entropyMust be on the opposite side
Minimum enthalpy
Entropy must increase
I’m Entropy
Enthalpy must increase
5. Describe the change in entropy and enthalpy for an exothermic equilibrium system.
Minimum enthalpy
Maximum entropy
Entropy is decreasing
Enthalpy is decreasing
I’m Entropy
6. Describe entropy and enthalpy as increasing or decreasing.
Zn(s) + 2HCl(aq) → H2(g) + ZnCl2(aq) ΔH = -252 KJ
√ max entropy
√ min enthalpy
Enthalpy decreases
Entropy increases
7. Describe entropy and enthalpy as increasing or decreasing.
3C(s) + 3H2(g) + 45 KJ → C3H6(g)
√ max entropy
√ min enthalpy
Enthalpy increases
Entropy decreases
Equilibrium is a compromise between the tendencies toward minimum enthalpy and maximum entropy.