Gen. Chem. Chapter 6

thermochemistry
the study of the relationship between chemistry and energy
energy
the capacity to do work
work
the result of a force acting through a distance
heat (q)
the flow of energy caused by a temperature difference
kinetic energy
the energy associated with motion of an object
thermal energy
a type of kinetic energy associated with the temperature of an object, arising from the motion of individual atoms or molecules in the object
potential energy
the energy associated with the position or composition of an object
chemical energy
the energy associated with the relative positions of electrons and nuclei in atoms and molecules
law of conservation of energy
a law stating that energy can neither be created nor destroyed, only converted from one form to another
system
in thermodynamics, the portion of the universe which is singled out for investigation
surroundings
in thermodynamics, everything in the universe which exists outside the system under investigation
joule (J)
the SI unit for energy; equal to 1 kg x m squared/s squared
calorie (cal)
a unit of energy defined as the amount of energy required to raise one gram of water 1 degree C; equal to 4.184 J
Calorie (Cal)
shorthand notation for the kilocalorie (kcal), or 1000 calories
kilowatt-hour (kWh)
an energy unit used primarily to express large amounts of energy produced by the flow of electricity; equal to 3.60 x 10^6 J
thermodynamics
the general study of energy and its interconversions
first law of thermodynamics
the law stating that the total energy of the universe is constant
internal energy (E)
the sum of the kinetic and potential energies of all of the particles that compose a system
state function
a function whose value depends only on the state of the system, not on how the system got to that state
thermal equilibrium
the point at which there is no additional net transfer of heat between a system and its surroundings
heat capacity (C)
the quantity of heat required to change a system;s temperature by 1 degree C
specific heat capacity (Cs)
the amount of heat required to raise the temperature of 1 g of a substance by 1 degree C
molar heat capacity
the amount of heat required to raise the temperature of one mole of a substance by 1 degree C
pressure-volume work
the work that occurs when a volume change takes place against an external pressure
calorimetry
the experimental procedure used to measure the heat evolved in a chemical reaction
bomb calorimeter
a piece of equipment designed to measure change in Erxn for combustion reactions at constant volume
enthalpy (H)
the sum of the internal energy of a system and the product of its pressure and volume; the energy associated with the breaking and forming bonds in a chemical reaction
endothermic reaction
a chemical reaction that absorbs heat from its surroundings; change in H > 0
exothermic reaction
a chemical reaction that releases heat to its surrounds; change in H < 0
enthalpy (heat) of reaction (change in Hrxn)
coffee-cup calorimeter
a piece of equipment designed to measure change in Hrxn for reactions at constant pressure
Hess’s Law
the law stating that if a chemical equation can be expressed as the sum of a series of steps, then change in Hrxn for the overall equation is the sum of the heats of reactions for each step
standard state
for a gas the standard state is the pure gas at a pressure of exactly 1 atm; for a liquid or solid the standard state is the pure substance in its most stable form at a pressure of 1 atm and the temperature of interest (often taken to be 25 degrees C); for a substance in solution the standard state is a concentration of exactly 1 M
standard enthalpy change (change in H degrees)
the change in enthalpy for a process when all reactants and products are in their standard states
standard enthalpy of formation (change in H degrees f)
the change in enthalpy when 1 mol of a compound forms from its constituent elements in their standard states
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