1. The reaction that occurs in heat packs used to treat sports injuries is shown below. How much heat is released when 1.00g of iron is reacted with excess O2 if the change in enthalpy for the reaction is kJ?
4Fe + 3O2 → 2Fe2O kJ
1.00g Fe x 1 mol Fe x kJ = kJ released
55.85 g Fe 4 mol Fe

2. -LOST heat (metal) = GAINED heat (water)
A 97 g sample of gold at 785oC is dropped into 323 g of water, which has an initial
temperature of 15oC. If gold has a specific heat of J/goC, what is the final
temperature of the mixture? Assume that the gold experiences no change in state
of matter.
-LOST heat (metal) = GAINED heat (water)
- [(sAu) (mass) (DT)] = (sH2O) (mass) (DT)
-[(0.129 J/goC)(97 g)(Tf - 785oC)] = (4.184 J/goC)(323 g)(Tf -15oC)
-[(12.5J/oC)(Tf - 785oC)]= (1.35x 103J/oC)(Tf -15oC)
(1.35x 103J/oC) (1.35x 103J/oC)
-[( )(Tf - 785oC)]= Tf -15oC
Tf oC = Tf -15oC
oC = Tf
Tf = oC → 22oC

3. Entropy (S) = disorder, randomness. The universe LOVES disorder
Entropy (S) = disorder, randomness. The universe LOVES disorder! Gibb's Free Energy (G) combines the idea of enthalpy (H) and entropy (S). Analyzing the change in Gibb's free energy will tell you whether something's going to happen, or not...called spontaneity.

4. Solid, liquid Gas… The universe LOVES disorder (high S), BUT...
The universe is also lazy (likes low H)
Ssolid < Sliquid << Sgas
Hsolid < Hliquid << Hgas

5. Gibbs Free Energy & Chemical Reactions
ΔG = ΔH – TΔS
If ΔG < 0, the reaction is spontaneous
If ΔG > 0, the reaction is not spontaneous
The reverse reaction is spontaneous
If ΔG = 0, the reaction is at equilibrium
Neither the forward nor the reverse happens

6. Effect of ΔH and ΔS on Spontaneity
ΔG = ΔH – TΔS
Remember… ΔG negative means spontaneous reaction 1 2 3 4 ΔH – + ΔS + –
Spontaneous?
(win/win) Spontaneous at all temps
(lose/win) Spontaneous at high temps
(win/lose) Spontaneous at low temps
(lose/lose) Not spontaneous at any temp

7. For example...is this reaction always, sometimes or never spontaneous?
4Fe + 3O2 → 2Fe2O kJ Hint… less gas, more solid means less disorder...negative delta S!

8. Most common units of energy
S unit of energy is the joule (J), energy is also expressed in kilojoules (1 kJ = 103J).
Non-S unit of energy is the calorie where 1 calorie (cal) is the amount of energy needed to raise the temperature of 1 g of water by 1°C.
One cal = J or 1J = cal.
Units of energy are the same, regardless of the form of energy
review your notes from the day we melted ice on the "cold" black square and the "hot" black square didn't melt the ice.
review old powerpoint presentations online!!

9. Exothermic Reaction Reactants  Products + Energy Energy Reactants -DH
Energy of reactants
Energy of products
Energy
Reactants
-DH
Products
Reaction Progress

10. Endothermic Reaction +DH Endothermic Energy Reaction progress
Energy + Reactants  Products
Products
Energy
+DH Endothermic
Reactants
Reaction progress

11. Specific Heat Water and silver do not transfer heat equally well.
Water has a specific heat Cp = J/goC
Silver has a specific heat Cp = J/goC
What does that mean?
It requires Joules of energy to heat 1 gram of water 1oC
and only Joules of energy to heat 1 gram of silver 1oC.
Law of Conservation of Energy…
In our situation (silver is “hot” and water is “cold”)…
this means water heats up slowly and requires a lot of energy
whereas silver will cool off quickly and not release much energy.