thermochemistry+part+02 - Principles of General Chemistry,...

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Chemical Thermodynamics: Heat and Thermochemistry Principles of General Chemistry, 2 nd ed. By M. Silberberg Chemistry, 8th ed. by W. Whitten, R. Davis, R., M. L. Peck, and G. Stanley. Exercises (True or False) 1. Enthalpy is an intensive property. 2. The 2 nd law of thermodynamics states that the entropy of a pure crystalline solid at 0 K is zero. 3. In Δ H measurements, standard conditions are defined as 25.0 °C and 1.00 atm . 4. Condensation is a process accompanied by an increase in Δ S. 5. A positive (+) heat (q) value for a system indicates that energy is absorbed by the system. Exercises (Problem Solving) 1. In burning of gasoline in a car engine, the system releases 325 J of heat to the surroundings. The expanding gases also do 451 J of work to push the pistons outward. Calculate the change in energy of the system (in cal). Exercises (Problem Solving) 2. Given the following thermochemical equation, how much heat (in kJ) evolves when 10.0 g of H 2 reacts with 5.00 g of Cl 2 to form the acid? H 2(g) + Cl 2(g) b 2 HCl (g) Δ H = -185 kJ/mol Exercises (Problem Solving) 3. Determine the Δ H°for the reaction which occurs in a welder’s acetylene torch. 2 C 2 H 2(g) + 5 O 2(g) b 4 CO 2(g) + 2 H 2 O (l) Use the following thermochemical equations: H 2(g) + ½ O 2(g) b H 2 O (l) Δ H = -285.8 kJ/mol 2 C (s) + H 2(g) b C 2 H 2(g) Δ H = +226.7 kJ/mol C (s) + O 2(g) b CO 2(g) Δ H = -393.5 kJ/mol 2nd Law of Thermodynamics In spontaneous changes, the universe tends towards a state of greater disorder .” Fundamental Laws
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Spontaneity of Physical and Chemical Changes • Spontaneous changes happen without any continuing outside influences . • A spontaneous change has a natural direction. • Example: rusting of iron & melting of ice at room temperature occurs spontaneously. Aspects of Spontaneity
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This note was uploaded on 07/24/2011 for the course CHEM 16 taught by Professor Siao during the Spring '07 term at University of the Philippines Diliman.

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thermochemistry+part+02 - Principles of General Chemistry,...

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