15.3+Entropy

# 15.3+Entropy - 15.3 ENTROPY The study of energy and how it...

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P a g e 15.3 ENTROPY The study of energy and how it changes is called thermodynamic. In thermodynamics, the object / reaction / change / process being studied is called the system and everything else is called the surroundings . The energy of the system and the surrounding is referred to as the ‘universe’ . Chemical substances have two types of energy 1. Kinetic – energy of molecular movement. There are three types – rotation, translation and vibration. Kinetic energy is useable energy because it makes particles move and can be transformed into other kinds of useful energy. 2. Potential – energy stored in chemical bonds. The amount of potential energy stored in a bond depends on the amount of electron-electron repulsion, electron-nucleus attraction and nucleus-nucleus repulsion and therefore depends on the radius, nuclear charge and number of bonding electrons. The total energy of a system is the sum of the potential and kinetic energies. Laws are generalizations, principles or patterns in nature and theories are the explanations of those generalizations. Many theories if sufficiently tested can become laws, but a theory is not needed to bestow lawlessness. The Laws of Energy/Thermodynamics These laws can be used to account for the change in energy that accompanies bond breaking and making during a chemical reaction. 1. The first law of thermodynamics or Law of conservation of energy Energy cannot be created or destroyed but can be transformed (converted) from one form to another. This means that the energy of the ‘universe’ does not change even though energy is being transformed from one form to another. If you lift a book off the table, and let it fall, the total energy of the ‘universe’ remained unchanged. 2. The second law of thermodynamics When energy is transformed from one form to another, some of its transferable ability (work) is lost as heat energy. The second law tells us that heat differs from other forms on energy in that it is not convertible. For example potential energy can be converted to kinetic energy and heat energy, however, complete conversion of heat into other forms of energy is not possible. One of the interesting things about thermodynamics is that although it deals with matter, it makes no assumptions about the nature of that matter. This is an important quality, because it means that laws and theories of thermodynamics are unlikely to change as new knowledge about the structure and bonding of matter comes to light. In thermodynamics entropy, S is a measure of the number of ways (probability) of arranging molecules so as to share their kinetic energy. As the probability increases, the entropy increases. Entropy

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## This note was uploaded on 04/09/2010 for the course SCIENCE CHEM taught by Professor M during the Spring '09 term at McMaster University.

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15.3+Entropy - 15.3 ENTROPY The study of energy and how it...

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