Flashcards in Chapter 5: energy, heat, and work Deck (93):
a complete chemical equation includes a quantitative measure of the
energy produced or consumed
thermochemistry is the study of the
relationship between heat and chemical reactions
all forms of energy fall into two categories:
kinetic energy and potential energy
kinetic energy is energy possessed by matter because it is
the kinetich energy of an object depends on both its
mass (m) and its velocity (v)
kinetic energy =
1/2m * v^2
The SI unit for energy is the
[(kilogram)(meter)^2] / (second)^2
thermal energy is kinetic energy in the form of
random motion of the particles in a sample of matter
the greater the temperature of the matter, the ... its particles move and the ...
faster; higher its thermal energy
heat is the flow of energy from ... that causes a change in the ...
one object to the other; temperature of the object
when heat is added to or removed from a sample, it causes a change in the
temperature of that sample
work is the application of a
force across some distance
it takes energy to perform .., so like heat, quantities of .. are expressed in units of ...
work; work; joules
work can take many forms: ... work, ... work, ... work, ... work, and ... work
mechanical; chemical; gravitational; pressure-volume; electrical
potential energy is energy possessed by matter because of its
position or condition
.... energy: compounds also possess ... as a result of the ...
chemical; potential energy; forces that hold the atoms together
in a chemical reaction, because the chemical energy of the reactants is not the same as that of the products, enrgy is either ... or ... during the reaction, usually in the form of ...
absorbed; released; heat
sample of matter
the system is the matter of
the surroundings are
all other matter
surroundings include the
law of conservation of energy states that the total energy of the ... is ... during a ...
universe; constant; chemical/physical change
system + surroundings
energy is often ... the system and the surrooundings
law of conservation of energy is also referred to as the
first law of thermodynamics
if energy transfers between the system and the surroundings, then the total amount of energy contained in the system has
energy change =
work + heat
exothermic: ... to the surroundings
endothermic: a reaction that
energy can be considered a
SI unit of heat energy is
a calorie was originally defined as the amount of heat needed to increase the .... by ..., from .. to ...
temperature of 1 g water; 1 degree celsius; 14.5 degrees C to 15.5 degrees C
1 cal =
thus, it takes ... J to increase the temperature of 1 g water from 14.5 degrees celsius to 15.5 degrees celsius
enthalpy, H, of a system is the measure of the
total energy of the system at a given pressure and temperature
enthalpy cannot be measured, but the ... that accompanies a change in the system can be measured
change in enthalpy
under conditions of constant pressure and temperature, the quanitity of heat ... at constant temperature and pressure is called the
absorbed/given off by the system; change in enthalpy
delta H means
Hfinal - Hinitial
if the chemical reaction is exothermic, the system has ..., which means that its enthalpy ... and delta H is ..
lost energy; decreases; negative
if the chemical reaction is endothermic, the enrgy of the system ... and the sign of delta H is ...
a thermochemical equation is a chemical equation for which
the value of delta H is given
the chemical reaction is assumed to occur at .., because delta H is used in the thermochemical equation
constant pressure and temperature
the enthalpy is determined by
in a thermochemical equation, delta H assumes that the coefficients refer to
it is important to include the ... of every substance in any ...
physical state; thermochemical equation
enthalpy changes are part of the ... of a thermochemical equation
the thermochemical equation expresses the stoichiometric relationship between the ... of any substance in the equation and the ...
number of moles; quantity of heat produced or absorbed in the reaction
calorimetry: measurement of the heat ... when the ... occurs
released or absorbed; chemical change
calorimeter: the device in which the ... and the ...
reaction takes place; heat is meausred
the quantity of heat released or absorbed by the reaction causes a change in the .... which is measured with a ...
temperature of the solution; thermometer
for the heat to correspond to the enthalpy change of the system, the calorimeter must be operated at
the reaction in the calorimeter proceeds at constant pressure because .. changes little during the course of the experiment
the insulation provided by the calorimeter prevents any
transfer of heat into or out of the calorimeter
in a calorimetry experiment, the amount of solution must be known because the observed temperature change depends on the
amount of solution present
the heat capacity of a sample is the quantity of heat required to
increase the temperature of that object by 1 K
heat capacity has units of ... or ..., and is nearly constant for a given substance over...
J/K; J/ degrees C; small ranges of temperature
the specific heat is the heat needed to ...
increase the temperature of a 1-g sample of the material by 1 K
heat in joules
mass in grams
specific heat of sample
(assumptions in calorimetry calculations) the heat required to change the temperature of the vessel, stirrer, and thermometer is
sufficiently small to be ignored
(assumptions in calorimetry calculations) the specific heat of the solution, as long as it is dilute, is the
same as that of water, 4.184 J/gK
a state function is any ... that is determeined by the ..
property of a system; present conditions of the system
the state function is independent of how the
system got to that set of conditions
the enthalpy, and the change in enthalpy, of a chemical system is a
the value of delta H for a process does not depend on how the
the delta H is only dependent of the ... of the system and the ... of the system
initial state; final state
in thermochemical equations, the coefficients refer to molar amounts, so
fractional coefficents can be used
energy-level diagrams are ... graphs
an energy-level diagram is a representation of the relative ... of the ...
enthalpies; reactnats and products of a reaction
reversing the direction of a chemical reaction ... on the reaction's deltaH
changes the sign
Hess's law: calculating the enthalpy change in an overall chemical reaction by
summing the enthalpy changes of each step
the properties that govern the combination of thermochemical equations are natural consequences of ... and the fact that ...
the law of conservation of energy; enthalpy is a state function
the change in enthalpy for an equation obtained by adding two or more thermochemical equations is the sum of the
enthalpy changes of the added equations
the enthalpy change is an ... that depends on the amounts of the substances that react
hess's law lets us calculate the enthalpy change for one reaction from
thermochemical equations for others
enthalpy change for any reaction is influenced by the
pressure and the temperature
standard state of a substance is the ... at ... and the ...
pure form; one atmosphere pressure; designated temperature (usually 298.15 K or 25.0 degrees C)
standard enthalpy change is an enthalpy change in which all
reactants and products are in their standard states
the symbol for standard enthalpy change is
° means that all reactants and products are in the standard state of
1 atm pressure and 298.15 K
a formation reaction is a chemical reaction that makes
one mole of a substane from its constituent elements in their standard states
the enthalpy change for a formation reaction is symbolized by
the subscript f stands for
ΔHf° is called
standard enthalpy of formation
the ΔHf° of all elements in their standard states is
∑mΔHf° [products] - ΣnΔHf° [reactants]
m is the number of moles of each
n is the number of moles of each
the reactants contribute the ... of their enthalpies of formation, whears products contribute the ... of their enthalpies of formation