thermochemistry Flashcards
theres two kinds of basic energy:
Potential (stored) and kinetic (motion)
Internal energy =
sum of all energy
On molecular scale, chemical bond energy =
potential energy stored in molecular clouds
energies of molecular moition =
Rotationa;, translational, vibrational
thermal energy
sometimes called energy of molecular motion
temperature is a common measure of
energy of molecular motion
ENERGY is the capacity to
do work or supply heat
1st law of thermodynamics
energy cannot be created or destroyed
All total energy of universe is ____
conserved
UNiverse equation
system + surroundings
If energy leaves the system, it must
enter the surroudings
energy change in energy system has to be accompanied by an _______ _______ change and the ____ must be ________
equal magnitude
signs
opposite
ΔE =
Eproducts - E reactants
state function
A function or property whose value depends only on the present state (condition) of the system (path doesn’t matter)
Example of state function
Arriving to Montreal with or with out layovers doesn’t matter. final position is the state function
Most changes to internal energy of system involve ______ of both _____ & ______
transfer
heat
work
ΔESYS =
work (w) - heat (q)
If w (work) = 0 then
it is example of energy transferred only as heat (q)
Heat or thermal energy will flow from _________ to _________ objects, eventually reaching _________ __________
higher-temp
lowe-temp
equal temp
When w = 0, ΔE < 0, q < 0 then
heat released to surrounding
(E initial > E final)
When w = 0, ΔE > 0, q > 0 then
heat absorbed to surrounding
(E intial < E final)
Mechanical work is the product of
w = force (F) x distance (d)
The larger the force or the longer the distance an object is moved, ….
the more work is done ON it
when is transfer of energy work only
when q = 0
When gas forming rxn in insulated container is attached to piston cylinder that pushes against it, the system
pushes the piston out, DOING WORK ON the surroundings
Expansion work
The work done when the volume of a system changes in the presence of an external pressure
Expansion work i also known as
Pressure volume work
Expansion work at constant pressure (P = P surroundings) the formula is
w = -PΔV = -P(V final - Vinitial)
More work is done when the volume change is
larger
The sign of expansion work is negative because
The system is expanding and doing work. It LOSES internal energy by doing this work
If the volume occupied by the reactants is larger than the volume occupied by the products,
Work is done on the system
Enthalpy is a scale to keep track of the ______ of the _______________ transformation
energenetics
constant-pressure
ENTHALPY (H) is defined as
H = E + PV
Change in enthalpy (ΔH) formula
ΔH = ΔE +PΔV
Change in enthalpy (ΔH) is equal to the amount of heat ________ or ______ in a ________ at CONSTANT PRESSURE
gained
loss
transformation
if ΔH < 0 then
if ΔH > 0 then
exothermic (heat loss, is a product)
endothermic (heat gain, is a reactant)
Multiplying a reaction increases ΔH by
reversing a reaction changes
by the same factor
the sign of ΔH
heat capacity definition
amount of heat required to raise the temperature of an object or substance by 1C or K
Heat capacity formula
q/ΔT
Sand heats up really quick so it has _____ heat capacity
LOW
Specific heat capacity definition and formula
Heat capacity per mass (1g)
c = q/(mass x ΔT)
Molar heat capacity definition and formula
Heat capacity per mole
c = q/ (amount mole x ΔT)
Energy is stored in different _______________
degrees of motion
Higher heat capacity means _____ ________ given off
more heat
Calorimetry
Science of measuring the heat exchanged in chemical reactions
In calorimetry, the heat of reaction (qrxn) is measured __________ by means of a calorimeter. If rxn produces heat, the temperature of surroundings _________ and vice versa
indirectly
increases
q rxn =
- q calorimeter
= -(qvessel + qsolution +qother)
example of constant pressure or coffee cup calorimetry
qsys (sample) = -q calorimeter (surrounding h20)
HEAT CAPACITY of the calorimeter (often equal ot that of the surrounding water cuz heat absorption of vessel is minimal) provides the link between _____________ and _________ from which you can determine the _____ ______ of the system
ΔT
Heat gained/lost
enthalpy change
Heat capacity (calorimeter) formula
q cal/ΔT cal
Standard states of
pure substance
gas
substance in aquoeous solution
1atm
1 atm
1M concentration
Standard enthalpy of a reactioon is indicated by symbol
ΔH° rxn
what does ΔH° rxn indicate`
enthalpy change noted corresponds to all reactants and all products being present IN Standard state
symbol for standard enthalpies of formation
also called
standard heat of formation
ΔH°f
ΔH°f is enthalpy change for the formation of ________ of substance in its ________ from its ________ elements in their standard states
1 mole
standard state
constituent
ΔH°f FORMULA
ΔH°f = ΔH°f (PRODUCTS) - ΔH°f (REACTANTS)
ΔH°f CAN BE approximated by
accounting for bonds broken and formed using fomrula
ΔHrxn° ~~ BE (reactant bonds) - BE (product bonds)
Hess law is
ΔH overall = ΔH1 + ΔH2 + ΔH3 …….
what is texts notation for hess hlaw:
it uses ∑mΔH°f(products) - ∑nΔH°f(reactants)
∑ is
m and n
sum of all
m and n is stoichiometric coefficients
Explain work done ON vs work done BY
Work done on = something outside increases the energy inside the system
work done by = systems internal energy decreased when it did work. (DONE BY* SYSTEM DOES THE WORK)
