1. 17-2 Driving Force of Reactions

2. p. 526
Are most reactions endothermic or exothermic?

3. p. 526 Are most reactions endothermic or exothermic?
Something other than enthalpy (ΔH) determines whether endothermic occurs spontaneously
A system that can go from one state to another WITHOUT an enthalpy change does so by becoming more ___________________

4. p. 526 Are most reactions endothermic or exothermic?
Something other than enthalpy determines whether endothermic occurs spontaneously
A system that can go from one state to another WITHOUT and enthalpy change does so by becoming more DISORDERED

5. 2NH4NO3(s)  2N2 (g) + 4H2O(l) + O2 (g)
Right side is more random arrangement
Tendency in nature is an increase in disorder
What is a disordered system? (p. 527)

6. 2NH4NO3(s)  2N2 (g) + 4H2O(l) + O2 (g)
Right side is more random arrangement
Tendency in nature is an increase in disorder
What is a disordered system? (p. 527)
Lacks arrangement of its parts
Entropy (s) -

7. 2NH4NO3(s)  2N2 (g) + 4H2O(l) + O2 (g)
Right side is more random arrangement
Tendency in nature is an increase in disorder
What is a disordered system? (p. 527)
Lacks arrangement of its parts
Entropy (S) - measure of randomness of particles
Solids
Liquids
gases

8. 2NH4NO3(s)  2N2 (g) + 4H2O(l) + O2 (g)
Right side is more random arrangement
Tendency in nature is an increase in disorder
What is a disordered system? (p. 527)
Lacks arrangement of its parts
Entropy (S) - measure of randomness of particles
Solids – low entropy
Melt – Liquids, increase entropy
Evaporate – Gas, increase entropy

9. Entropy Change ΔS Difference of products and reactants
Increase in entropy = + ΔS
Decrease in entropy = - ΔS
Making solutions increases ΔS
Mixing gases
Liquid into another liquid
Solids dissolved in liquid
Fig (p. 528)

10. p. 528 Processes are driven in 2 directions:
Toward lowest enthalpy (lowest ΔH) OR
Highest entropy (highest ΔS)
Free Energy (G) – combined H and S function
Only change can be measured
Free energy change – ΔG
Equation:

11. p. 528 Processes are driven in 2 directions:
Toward lowest enthalpy (lowest ΔH) OR
Highest entropy (highest ΔS)
Free Energy (G) – combined H and S function
Only change can be measured
Free energy change – ΔG
Equation: ΔG = ΔH - T ΔS (T in Kelvin)

12. Table p. 529 ΔG = ΔH - T ΔS Each can be positive or negative
When change in different directions one will usually predominate

13. Example p. 530

14. More Order or More disorder? ΔS = + or -?
2 Fe2O3(s) --> 4 Fe(s) + 3 O2(g)
W(s) + 6 CO(g) --> W(CO)6(s)
C6H12O6(s) --> C6H12O6(aq)
H2O(g) --> H2O(ℓ)