1. Aim: What is entropy?

2. Spontaneous Reaction
A spontaneous reaction is one that is able to proceed without needing an outside source of energy
A nonspontaneous reaction needs an input of energy.

3. Spontaneous reactions occur in the direction of:
Less energy (lower enthalpy): exothermic reactions are favored
Greater entropy (randomness, disorder)

4. Enthalpy (H) In nature, reactions tend to favor a lower energy state.
Products with less Potential Energy than the reactants are favorable.
CH4(g) + 2O2(g)  CO2(g) + 2H2O(l) ΔH= KJ

5. Entropy

6. Entropy
Entropy (S); Measure of disorder or randomness in a system. In nature greater entropy is favored.
Which had greater entropy?

7. Entropy
1. Which phase will have the greatest entropy? The least entropy?

8. Entropy in Chemical Reactions
Entropy increases:
When the number of molecules increases during a reaction.
With an increase in temperature
When a gas is formed from a liquid or a solid.
When a liquid is formed from a solid.

9. Questions
1. Which tendencies favor a spontaneous reaction? 1) lower energy and decreasing entropy 2) lower energy and increasing entropy 3) higher energy and decreasing entropy 4) higher energy and increasing entropy

10. Questions
2. Which reaction system tends to become less random as reactants form products? (1) C(s) + O2(g) --> CO2(g) (2) S(s) + O2(g) --> SO2(g) (3) I2(s) + Cl2(g) --> 2ICl (g) (4) 2Mg (s) + O2(g) --> 2MgO (s)

11. Questions
3. As NaCl(s) dissolves according to the equation NaCl(s) --> Na+ (aq) + Cl- (aq) the entropy of the system (1) decreases (2) increases (3) remains the same