Chap 15 - 15 Chemical Thermodynamics 1 The First Law of...

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1 15 Chemical Thermodynamics
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2 The First Law of Thermodynamics Thermodynamics is the study of the changes in energy and transfers of energy that accompany chemical and physical processes. In this chapter we will address 3 fundamental questions.
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3 The First Law of Thermodynamics 1. Will two (or more) substances react when they are mixed under specified conditions? 2. If they do react, what energy changes and transfers are associated with their reaction? 3. If a reaction occurs, to what extent does it occur?
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4 The First Law of Thermodynamics Exothermic reactions release energy in the form of heat. For example, the combustion of propane is exothermic. kJ 10 2.22 O 4H CO 3 O 5 H C 3 ) ( 2 2(g) 2(g) (g) 8 3 × + + + l
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5 The First Law of Thermodynamics The combustion of n-butane is also exothermic. kJ 10 5.78 O H 10 CO 8 O 13 H C 2 3 ) ( 2 2(g) 2(g) 10(g) 4 × + + + l For an exothermic reaction, the potential energies of the products are lower than the potential energies of the reactants.
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6 The First Law of Thermodynamics
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7 The First Law of Thermodynamics There are two key postulates for thermodynamic systems. 1. Chemical systems tend toward a state of minimum potential. 2. Chemical systems tend toward a state of maximum disorder .
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8 The First Law of Thermodynamics This law can be stated as, “ The total energy in the universe is constant .” The First Law of Thermodynamics is also known as the Law of Conservation of Energy - law states that energy is neither created nor destroyed in chemical reactions and physical changes.
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9 Some Thermodynamic Terms The substances involved in the chemical and physical changes under investigation are called the system . In chemistry lab, the system is the chemicals inside the beaker.
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10 Some Thermodynamic Terms The environment around the system is called the surroundings (surroundings are outside the beaker). The system plus the surroundings is called the universe . The set of conditions that specify all of the properties of the system is called the thermodynamic state of a system .
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11 Some Thermodynamic Terms The thermodynamic state could include: 1) The number of moles and identity of each substance. 2) The physical states of each substance. 3) The temperature of the system. 4) The pressure of the system.
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12 Some Thermodynamic Terms The properties of a system that depend only on the state of the system are called state functions . State functions are always written using capital letters. The value of a state function is independent of pathway.
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13 Some Thermodynamic Terms An analog to a state function is the energy required to climb a mountain taking two different paths. E 1 = energy at the bottom of the mountain E 1 = mgh 1 E 2 = energy at the top of the mountain E 2 = mgh 2 Δ E = E 2 -E 1 = mgh 2 –mgh 1 = mg( Δ h)
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14 Some Thermodynamic Terms Notice that the energy change in moving from the top to the bottom is independent of pathway but the work required may not be!
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This note was uploaded on 09/18/2010 for the course CHEM 1212 taught by Professor Suggs during the Fall '08 term at University of Georgia Athens.

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Chap 15 - 15 Chemical Thermodynamics 1 The First Law of...

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