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.

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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 -1652 kJ? 4Fe + 3O2 → 2Fe2O3 + 1652 kJ 1.00g Fe x 1 mol Fe x 1652 kJ = 7.39 kJ released 55.85 g Fe 4 mol Fe

-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 0.129 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) -[(0.009259 )(Tf - 785oC)]= Tf -15oC - 0.009259 Tf + 7.268 oC = Tf -15oC 22.268 oC = 1.009259Tf Tf = 22.0637oC → 22oC

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.

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

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

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

For example...is this reaction always, sometimes or never spontaneous? 4Fe + 3O2 → 2Fe2O3 + 1652 kJ Hint… less gas, more solid means less disorder...negative delta S!

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 = 4.184 J or 1J = 0.2390 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!!

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

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

Specific Heat Water and silver do not transfer heat equally well. Water has a specific heat Cp = 4.184 J/goC Silver has a specific heat Cp = 0.235 J/goC What does that mean? It requires 4.184 Joules of energy to heat 1 gram of water 1oC and only 0.235 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.