Term
| absolute entropy (of a substance) |
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Definition
| The entropy of a substance relative to its entropy in a perfectly ordered crystalline form at 0 K (where its entropy is zero). |
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Term
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Definition
| A device used to measure the heat transfer between system and surroundings at constant volume. |
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Term
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Definition
| The amount of energy necessary to break one mole of bonds in a gaseous substance to form gaseous products at the same temperature and pressure. |
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Term
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Definition
| A device used to measure the heat transfer that accompanies a physical or chemical change. |
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Term
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Definition
| The degree to which the total energy of a system can be distributed among its particles. |
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Term
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Definition
| The degree to which the particles of a sample can be distributed in space; also called disorder. |
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Term
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Definition
| A process that absorbs heat. |
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Term
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Definition
| The quantity of heat transferred into or out of a system as it undergoes a chemical or physical change at constant temperature and pressure. |
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Term
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Definition
| A thermodynamic state property that measures the dispersal of energy and the dispersal of matter (disorder) of a system. |
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Term
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Definition
| A state of dynamic balance in which the rates of forward and reverse processes (reactions) are equal; the state of a system when neither the forward nor the reverse process is thermodynamically favored. |
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Term
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Definition
| A process that gives off (releases) heat. |
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Term
| First Law of Thermodynamics |
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Definition
| The total amount of energy in the universe is constant (also known as the Law of Conservation of Energy); energy is neither created nor destroyed in ordinary chemical reactions and physical changes. |
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Term
| Gibbs free energy change, ?G |
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Definition
| The indicator of spontaneity of a process at constant T and P. ?G = ?H – T?S. If ?G is negative, the process is product-favored (spontaneous); also called free energy change. |
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Term
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Definition
| The thermodynamic state function of a system that indicates the amount of energy available for the system to do useful work at constant T and P. It is defined as G = H – TS; also called free energy. |
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Term
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Definition
| See Standard molar enthalpy of formation. |
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Term
| Hess's Law of Heat Summation |
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Definition
| The enthalpy change for a reaction is the same whether it occurs in one step or a series of steps. |
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Term
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Definition
| All forms of energy associated with a specific amount of a substance. |
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Term
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Definition
| The energy of motion. The kinetic energy of an object is equal to one half its mass times the square of its velocity. |
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Term
| Law of Conservation of Energy |
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Definition
| Energy cannot be created or destroyed in a chemical reaction or in a physical change; it may be changed from one form to another; see First Law of Thermodynamics. |
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Term
| mole of reaction (mol rxn) |
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Definition
| The amount of reaction that corresponds to the number of moles of each substance shown in the balanced equation. |
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Term
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Definition
| See Reactant-favored change. |
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Term
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Definition
| The energy that a system or object possesses by virtue of its position or composition. |
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Term
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Definition
| Work done by a gas when it expands against an external pressure, or work done on a system as gases are compressed or consumed in the presence of an external pressure. |
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Term
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Definition
| A change for which the collection of products is more stable than the collection of reactants under the given conditions; also called spontaneous change. |
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Term
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Definition
| A change for which the collection of reactants is more stable than the collection of products under the given conditions; also called nonspontaneous change. |
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Term
| Second Law of Thermodynamics |
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Definition
| The universe tends toward a state of greater disorder in spontaneous processes. |
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Term
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Definition
| See Product-favored change. |
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Term
| standard enthalpy change, ?H0 |
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Definition
| The enthalpy change in which the number of moles of reactants specified in the balanced chemical equation, all at standard states, is converted completely to the specified number of moles of products, all at standard states. |
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Term
| standard entropy change, ?S0 |
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Definition
| The entropy change in which the number of moles of reactants specified in the balanced chemical equation, all at standard states, is converted completely to the specified number of moles of products, all at standard states. |
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Term
| standard molar enthalpy of formation, ?H0f (of a substance) |
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Definition
| The enthalpy change for the formation of one mole of a substance in a specified state from its elements in their standard states; also called standard molar heat of formation or just heat of formation. |
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Term
| standard molar entropy, S0 (of a substance) |
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Definition
| The absolute entropy of a substance in its standard state at 298 K. |
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Term
| standard molar heat of formation |
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Definition
| See Standard molar enthalpy of formation. |
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Term
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Definition
| A reaction in which the numbers of moles of reactants shown in the balanced equation, all in their standard states, are completely converted to the numbers of moles of products shown in the balanced equation, also all at their standard states. |
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Term
| standard state (of a substance) |
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Definition
| See Thermodynamic standard state of a substance. |
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Term
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Definition
| A variable that defines the state of a system; a function that is independent of the pathway by which a process occurs. |
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Term
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Definition
| Everything in the environment of the system. |
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Term
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Definition
| The substances of interest in a process; the part of the universe under investigation. |
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Term
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Definition
| A balanced chemical equation together with a designation of the corresponding value of ?Hrxn. Sometimes used with changes in other thermodynamic quantities. |
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Term
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Definition
| The observation, measurement, and prediction of energy changes for both physical changes and chemical reactions. |
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Term
| thermodynamic standard state of a substance |
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Definition
| The most stable state of the substance at one atmosphere pressure and at some specific temperature (25°C unless otherwise specified). |
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Term
| thermodynamic state of a system |
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Definition
| A set of conditions that completely specifies all of the properties of the system. |
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Term
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Definition
| The study of the energy transfers accompanying physical and chemical processes. |
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Term
| Third Law of Thermodynamics |
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Definition
| The entropy of a hypothetical pure, perfect, crystalline substance at absolute zero temperature is zero. |
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Term
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Definition
| The system plus the surroundings. |
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Term
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Definition
| The application of a force through a distance; for physical changes or chemical reactions at constant external pressure, the work done on the system is –P V; for chemical reactions that involve gases, the work done on the system can be expressed as –( n)RT. |
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