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Physical chemistry is the study of macroscopic, atomic, subatomic, and particulate phenomena in chemical systems in terms of laws and concepts of physics. It applies the principles, practices and concepts of physics such as motion, energy, force, time, thermodynamics, quantum chemistry, statistical mechanics and dynamics, equilibrium. Physical chemistry, in contrast to chemical physics, is predominantly (but not always) a macroscopic or supra-molecular science, as the majority of the principles on which physical chemistry was founded are concepts related to the bulk rather than on molecular/atomic structure alone. For example, chemical equilibrium, and colloids. Some of the relationships that physical chemistry strives to resolve include the effects of: #Intermolecular forces that act upon the physical properties of materials (plasticity, tensile strength, surface tension in liquids). #Reaction kinetics on the rate of a reaction. #The identity of ions and the electrical conductivity of materials. #Surface chemistry and electrochemistry of membranes. #Interaction of one body with another in terms of quantities of heat and work called thermodynamics. #Transfer of heat between a chemical system and its surroundings during change of phase or chemical reaction taking place called thermochemistry #Study of colligative properties of number of species present in solution. #Number of phases, number of components and degree of freedom (or variance) can be correlated with one another with help of phase rule. #Reactions of electrochemical cells. == Key concepts == The key concepts of physical chemistry are the ways in which pure physics is applied to chemical problems. One of the key concepts in classical chemistry is that all chemical compounds can be described as groups of atoms bonded together and chemical reactions can be described as the making and breaking of those bonds. Predicting the properties of chemical compounds from a description of atoms and how they bond is one of the major goals of physical chemistry. To describe the atoms and bonds precisely, it is necessary to know both where the nuclei of the atoms are, and how electrons are distributed around them.〔Atkins, Peter and Friedman, Ronald (2005). ''Molecular Quantum Mechanics'', p. 249. Oxford University Press, New York. ISBN 0-19-927498-3.〕 Quantum chemistry, a subfield of physical chemistry especially concerned with the application of quantum mechanics to chemical problems, provides tools to determine how strong and what shape bonds are,〔 how nuclei move, and how light can be absorbed or emitted by a chemical compound.〔Atkins, Peter and Friedman, Ronald (2005). ''Molecular Quantum Mechanics'', p. 342. Oxford University Press, New York. ISBN 0-19-927498-3.〕 Spectroscopy is the related sub-discipline of physical chemistry which is specifically concerned with the interaction of electromagnetic radiation with matter. Another set of important questions in chemistry concerns what kind of reactions can happen spontaneously and which properties are possible for a given chemical mixture. This is studied in chemical thermodynamics, which sets limits on quantities like how far a reaction can proceed, or how much energy can be converted into work in an internal combustion engine, and which provides links between properties like the thermal expansion coefficient and rate of change of entropy with pressure for a gas or a liquid.〔Landau, L. D. and Lifshitz, E. M. (1980). ''Statistical Physics'', 3rd Ed. p. 52. Elsevier Butterworth Heinemann, New York. ISBN 0-7506-3372-7.〕 It can frequently be used to assess whether a reactor or engine design is feasible, or to check the validity of experimental data. To a limited extent, quasi-equilibrium and non-equilibrium thermodynamics can describe irreversible changes.〔Hill, Terrell L. (1986). ''Introduction to Statistical Thermodynamics'', p. 1. Dover Publications, New York. ISBN 0-486-65242-4.〕 However, classical thermodynamics is mostly concerned with systems in equilibrium and reversible changes and not what actually does happen, or how fast, away from equilibrium. Which reactions do occur and how fast is the subject of chemical kinetics, another branch of physical chemistry. A key idea in chemical kinetics is that for reactants to react and form products, most chemical species must go through transition states which are higher in energy than either the reactants or the products and serve as a barrier to reaction.〔Schmidt, Lanny D. (2005). ''The Engineering of Chemical Reactions'', 2nd Ed. p. 30. Oxford University Press, New York. ISBN 0-19-516925-5.〕 In general, the higher the barrier, the slower the reaction. A second is that most chemical reactions occur as a sequence of elementary reactions,〔Schmidt, Lanny D. (2005). ''The Engineering of Chemical Reactions'', 2nd Ed. p. 25, 32. Oxford University Press, New York. ISBN 0-19-516925-5.〕 each with its own transition state. Key questions in kinetics include how the rate of reaction depends on temperature and on the concentrations of reactants and catalysts in the reaction mixture, as well as how catalysts and reaction conditions can be engineered to optimize the reaction rate. The fact that how fast reactions occur can often be specified with just a few concentrations and a temperature, instead of needing to know all the positions and speeds of every molecule in a mixture, is a special case of another key concept in physical chemistry, which is that to the extent an engineer needs to know, everything going on in a mixture of very large numbers (perhaps of the order of the Avogadro constant, 6 x 1023) of particles can often be described by just a few variables like pressure, temperature, and concentration. The precise reasons for this are described in statistical mechanics,〔Chandler, David (1987). ''Introduction to Modern Statistical Mechanics'', p. 54. Oxford University Press, New York. ISBN 978-0-19-504277-1.〕 a specialty within physical chemistry which is also shared with physics. Statistical mechanics also provides ways to predict the properties we see in everyday life from molecular properties without relying on empirical correlations based on chemical similarities.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Physical chemistry」の詳細全文を読む スポンサード リンク
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