1. ∆S and ∆H of fusion CHEMISTRY 1105

2. What are we going to do today?  Entropy ∆S  Melting Ice.  Use the thermistor to record the temperature  Use time vs temperature  select edit and calibrate reading file model 103.  Use a magnetic stir be careful not the hot the thermistor

3. Thermodynamics Gibbs Free energy is dependent of three things ΔG = ΔH – T ΔS Recognize them? o We will measure Temperature to calculate Enthalpy and thereafter entropy

4. More thermo. o Remember this: o G < 0 = Spontaneous o G = 0 = Equilibrium o G > 0 = Nonspontaneous o Is G = 0 at the phase change ? o Yes. But…. Why? o The system is at equilibrium 50 liquid / 50 solid o So... If ∆G = 0 then: o -∆ H =T ∆ S ( enthalpy of fusion for melting of ice) o ∆ S = ∆ H/T ( entropy of fusion for melting of ice)

5. How do we measure Entropy?  Measure the disorder in the system.  We are going to use a phase transition because G = 0 at the phase change.  change of entropy is associated with a heat exchange between the phases in contact.

6. Heat Transfer  Q Surroundings  Will measure the amount of heat transfer  So then : Q Surr. = Cp * m * ∆T  -Q surr = Q sys  And ∆ H = Q sys / moles of ice

7. Experiment  In the experiment  Measure the transition from solid to liquid  The system is reaching equilibrium so G =0  Assume the change in pressure is small and temp at transition is the same.  We can not measure the equilibrium conc. Because there will be no change in enthalpy and temperature

8. Procedure  Get a Styrofoam Cup or beaker (TA will tell you which)  USE a small beaker no more than 100ml  Dry the material well  Mass the dry cup (beaker) and record (#1)  Use the DI water  Specific heat of water is 4.18 j / gºC fill cup 2/3 full  Place the ice in the beaker and record after the ice have melted.

9. Comments  Add the cubes of ice to the water with out splashing  Stir gently and constantly  Temperature will drop  Record the lowest temp.  Use the same balance though out experiment.  Use units and Significant figures if not they will be counted as negative points