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CH. 15 CHEMICAL THERMODYNAMICS (Part 1)

CH. 15 CHEMICAL THERMODYNAMICS (Part 1) - CH 15 CHEMICAL...

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CH. 15: CHEMICAL THERMODYNAMICS (Part 1) Chemical thermodynamics deals with the study of energy changes in physical and chemical processes. In thermodynamics, we study the interconversions of various forms of energy like mechanical energy, light energy, electrical energy, and chemical energy in the macroscopic system. Thermodynamics also allows us to predict whether a certain change will occur and what maximum yield can be obtained. System and Surroundings In discussing thermodynamics, we must be careful to first define what is it that we are studying. It is convenient to divide the universe into two parts: the system and its surroundings . The part of the universe taken for thermodynamic study is called the system , while the rest of the universe is the surrounding . A system may be as simple as a flask of gas or as complicated as a chemical reactor. Types of Systems Open System is one which can exchange matter and energy with the surroundings. Closed System is one which can exchange energy, but not matter with the surroundings. Isolated System is one which can exchange neither matter nor energy with the surroundings. State of a System and State Functions Thermodynamic state of a system is a set of conditions that uniquely describes the system. This set of conditions includes temperature, pressure, volume, number of moles, physical state of the substances, etc. Once the state of the system is defined all other properties of the system are fixed. E.g. ‘five moles of oxygen gas at 200 K and 1.2 atm pressure’ defines a unique state of the system. In this state the density of the gas, the volume of the gas and the mass of the gas have a definite value which can be calculated. The set of conditions or properties that uniquely define the system are called state functions . Properties such as temperature, pressure, volume, number of moles, and physical state of the substances are examples of state functions. The value of a state function only depends on the state of the system and not on the way in which the system came to be in that state. When a system undergoes change (change of state), the change in value of a state function depends only on the value of the state function in the final and initial states. It is not dependent on how the change is brought about. In other words, a state function is not dependent on the path taken for going from initial to final state. The change in value of a state function, say temperature T, is given by: T = T final – T initial …………………………………………………………………..(1) Work and heat are modes of energy transfer to and from the system. Work and heat are not state functions, and their values depend on the path the system takes to go from intitial to final state.
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