Week 3-2 Lecture Notes.docx - Chem 125 Lecture Notes Week 3-2 Learning Objectives • • • • Gibbs Free energy and temperature could we change

Week 3-2 Lecture Notes.docx - Chem 125 Lecture Notes Week...

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Chem 125 Lecture Notes Week 3-2 Learning Objectives: Gibbs Free energy and temperature, could we change spontaneity with change of T? Kinetic vs Thermodynamic Describe the nature of equilibrium systems, Derive reaction quotients from chemical equations representing homogeneous and heterogeneous reactions Different forms of equilibrium constant (Kc, Kp, Ksp, Ka, Kf) Relate equilibrium concept to thermodynamic (K and Gibbs free energy) PQ7: “A diamond is forever” is one of the most successful advertising slogans of all time. But is it true? For the reaction shown below, calculate the standard free energy change at 298K and determine whether a diamond is “forever”. C(diamond) C(graphite) C(diamond) C(graphite) Δ H f °( kJ/mol) 1.895 S ° (J mol -1 K -1 ) 2.337 5.740 a) Δ G ° = 2.19 kJ; forever b) Δ G ° = –1.90 kJ; not forever c) Δ G ° = –2.90 kJ; not forever d) Δ G ° = 1.90 kJ; forever Kinetic vs. Thermodynamics The spontaneity of a process is not correlated to the speed of the process. A spontaneous change may be so rapid that it is essentially instantaneous or so slow that it cannot be observed over any practical period of time. In this particular case, diamonds are said to be thermodynamically unstable but kinetically stable under ambient conditions. The Third Law of Thermodynamics the entropy of a pure, perfect crystalline substance at 0 K is zero. S = k ln W = k ln(1) = 0 Gibbs Activity: Check answers for Q1 around your desk 1
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Chem 125 Lecture Notes Week 3-2 Temperature Dependence of Spontaneity Example: Explain what happens as a reaction starts with ΔG < 0 (negative) and reaches the point where ΔG = 0.
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  • Spring '08
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