Professor Dave problem from yesterday Do this problem as Today’s bellwork How much energy in joules is required to heat 35.3g of water from - 20C to 115C? ∆Hfus = 334 J/g ∆Hvap = 2260 J/g Cpice = 2.06 J/gC Cpwater = 4.184 J/gC Cpsteam = 2.02 J/gC Remember to split this problem into 5 pieces and add up the answers: Q for ice from -20->0 Melt ice Q for water from 0->100 Boil Water Q for steam from 100-115

Example H2O (s)  H2O (l) ∆Hfus = 333 J/g How much energy is needed to melt 10.5 g of ice? H2O (s)  H2O (l) ∆Hfus = 333 J/g

Example #2 How much energy is needed to condense 2.5 g of H2O? ∆Hvap = 2260 J/g

Heating Curves Shows how the temperature of a substance changes as heat is added.

Super Awesome Sample Problem How much heat is required to change 36 g of H2O from -8 deg C to 120 deg C? Step 1: Heat the ice (Cice = 2.06 J/gC) Q=mcΔT Q = 36 g x 2.06 J/g deg C x 8 deg C = 593.28 J = 0.59 kJ Step 2: Convert the solid to liquid ΔH fusion Q = 2.0 mol x 6.01 kJ/mol = 12 kJ Step 3: Heat the liquid (CH2O = 4.184 J/gC) Q=mcΔT Q = 36g x 4.184 J/g deg C x 100 deg C = 15063 J = 15 kJ

Now, add all the steps together Super Awesome Sample Problem How much heat is required to change 36 g of H2O from -8 deg C to 120 deg C? Step 4: Convert the liquid to gas ΔH vaporization Q = 2.0 mol x 44.01 kJ/mol = 88 kJ Step 5: Heat the gas (Cgas = 2.02 J/gC) Q=mcΔT Q = 36 g x 2.02 J/g deg C x 20 deg C = 1454.4 J = 1.5 kJ Now, add all the steps together 0.59 kJ + 12 kJ + 15 kJ + 88 kJ + 1.5 kJ = 118 kJ

The laws of thermodynamics First Law of Thermodynamics: Energy cannot be created or destroyed, but converted from one form to another. Second Law of Thermodynamics: The universe favors an increase of disorder (entropy) Third Law of Thermodynamics: The entropy of a pure substance at 0 K is 0. More simply, as you approach 0K, you approach 0 entropy (disorder)

Two trends in Nature High energy  low energy Order  Disorder

Ssolid < Sliquid < S gas Entropy Entropy (S) is a measure of the randomness or disorder of a system. If disorder increases, entropy increases. If order increases, entropy decreases. For any substance, the solid state is more ordered than the liquid state, which is more ordered than the gas state. Ssolid < Sliquid < S gas H2O (s)  H2O (l) ∆S > 0