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Chesnut Chem 1212k Ch 15 Vocabulary
Ch 15 Vocabulary
45
Chemistry
Undergraduate 2
06/21/2011

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Term
absolute entropy (of a substance)
Definition
The entropy of a substance relative to its entropy in a perfectly ordered crystalline form at 0 K (where its entropy is zero).
Term
bomb calorimeter
Definition
A device used to measure the heat transfer between system and surroundings at constant volume.
Term
bond energy
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.
Term
calorimeter
Definition
A device used to measure the heat transfer that accompanies a physical or chemical change.
Term
dispersal of energy
Definition
The degree to which the total energy of a system can be distributed among its particles.
Term
dispersal of matter
Definition
The degree to which the particles of a sample can be distributed in space; also called disorder.
Term
endothermic process
Definition
A process that absorbs heat.
Term
enthalpy change, ?H
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.
Term
entropy, S
Definition
A thermodynamic state property that measures the dispersal of energy and the dispersal of matter (disorder) of a system.
Term
equilibrium
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.
Term
exothermic process
Definition
A process that gives off (releases) heat.
Term
First Law of Thermodynamics
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.
Term
Gibbs free energy change, ?G
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.
Term
Gibbs free energy, G
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.
Term
heat of formation
Definition
See Standard molar enthalpy of formation.
Term
Hess's Law of Heat Summation
Definition
The enthalpy change for a reaction is the same whether it occurs in one step or a series of steps.
Term
internal energy, E
Definition
All forms of energy associated with a specific amount of a substance.
Term
kinetic energy
Definition
The energy of motion. The kinetic energy of an object is equal to one half its mass times the square of its velocity.
Term
Law of Conservation of Energy
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.
Term
mole of reaction (mol rxn)
Definition
The amount of reaction that corresponds to the number of moles of each substance shown in the balanced equation.
Term
nonspontaneous change
Definition
See Reactant-favored change.
Term
potential energy
Definition
The energy that a system or object possesses by virtue of its position or composition.
Term
pressure–volume work
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.
Term
product-favored change
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.
Term
reactant-favored change
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.
Term
Second Law of Thermodynamics
Definition
The universe tends toward a state of greater disorder in spontaneous processes.
Term
spontaneous change
Definition
See Product-favored change.
Term
standard enthalpy change, ?H0
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.
Term
standard entropy change, ?S0
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.
Term
standard molar enthalpy of formation, ?H0f (of a substance)
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.
Term
standard molar entropy, S0 (of a substance)
Definition
The absolute entropy of a substance in its standard state at 298 K.
Term
standard molar heat of formation
Definition
See Standard molar enthalpy of formation.
Term
standard reaction
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.
Term
standard state (of a substance)
Definition
See Thermodynamic standard state of a substance.
Term
state function
Definition
A variable that defines the state of a system; a function that is independent of the pathway by which a process occurs.
Term
surroundings
Definition
Everything in the environment of the system.
Term
system
Definition
The substances of interest in a process; the part of the universe under investigation.
Term
thermochemical equation
Definition
A balanced chemical equation together with a designation of the corresponding value of ?Hrxn. Sometimes used with changes in other thermodynamic quantities.
Term
thermochemistry
Definition
The observation, measurement, and prediction of energy changes for both physical changes and chemical reactions.
Term
thermodynamic standard state of a substance
Definition
The most stable state of the substance at one atmosphere pressure and at some specific temperature (25°C unless otherwise specified).
Term
thermodynamic state of a system
Definition
A set of conditions that completely specifies all of the properties of the system.
Term
thermodynamics
Definition
The study of the energy transfers accompanying physical and chemical processes.
Term
Third Law of Thermodynamics
Definition
The entropy of a hypothetical pure, perfect, crystalline substance at absolute zero temperature is zero.
Term
universe
Definition
The system plus the surroundings.
Term
work
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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