Thermochemistry Flashcards
System
the matter that is being observed; total amount of reactants and products in a chemical reaction
Surroundings/Enviornment
everything out side the system
If we are looking at the coffee as the system and the cup as the enviornment, what heat transfer are we studying?
Heat transfer between coffee and the cup
Isolated System
Environment and System do not exchange energy (heat/work) or matter
Closed System
System and Environment exchange energy but not matter
Open System
system and environment exchange both energy and matter
First Law of Thermodynamics
change in internal energy of a system is equal to the sum of heat added to the system minus work done by the system
U = Q - W
Isothermal Process
temperature is constant
Internal energy, U, is constant = 0
Work done by system = heat added to the system
Q = W
hyperbolic
Adiabatic Process
No heat exchange; Q = 0
change in internal energy of the system is opposite of work done by system
U = -W
extremely hyperbolic
Isobaric Process
Pressure is constant
no affect on first law
flat line
Isovolumetric/Isochoric Process
Volume is constant
no work is performed ; W = 0
change in energy is equal to energy placed into the system
U = Q
vertical line
Spontaneous Process
occurs by itself without having to be driven by energy from an outside source
State Functions
pressure, density, temperature, volume, enthalpy, internal energy, gibbs free energy, entropy
when the state of a system changes, one or more of these will change
Standard Conditions
298k
1 atm
1 M
Phase Changes
are reversible, and an equilibrium of phases will be given for a combination of temperature and pressure
ex: 0 degrees C and 1 atm pressure ic e and water are at equilibrium soice absorbs heat to become water but the water lsoes heat and becomes ice keeping relatively equal amounts
Phase equilibrium are analogous to the dynamic equilibrium of _________: the concentration of reactants and products are constant because the rates ____ and _____ are equal.
reversible chemical reactions
forward
reverse reactions
Not all molecules possess the same instantaneous speeds, meaning not the same instantaneous kinetic energy values. In the liquid phase, the molecules near the surface of the liquid have _________ to leave the liquid phase and enter the ______. This is known as _______.
enough kinetic energy
gas
evaporation/vaporization
Evaporation is an ________ process where the heat source is ______
endothermic process
liquid water
Boiling
a specific type of vaporization where the entire liquid bubbles and there is rapid release of liquid to gas particles once the BP is met
Condensation
gas molecules forced back to liquid molecules based on pressure or low temperature
Vapor Pressure
pressure exerted on the liquid by the gas
increases as temperature increases because mroe liquid particles can escape into gas
Boiling point
where vapor pressure is equal to the ambient/applied pressure
Whereas pure crystalline solids have ditinct _______, amorphous solids like glass, plastix, chocolate _______ over a _______ of temperatures due to their less ordered molecular structure
melting points
melt/solidify
range
Sublimation
solid to gas directly
Deposition
gas to solid directly
Triple Point
temperature and pressure where all 3 phases are in equilibria
Critical Point
between liquid and gas phase where there is no distinction between liquid and gas
called supercritical fluids
density of liquid and gas are equal
Temperature
avg kinetic energy of particles in a substance
Enthalpy (Thermal ENergy)
heat under constant pressure
Heat
transfer of energy from one substance to another resulting from a difference in temperatures
Endothermic
process where system absorbs heat
delta Q > 0
Exothermic
process where system releases heat
delta Q < 0
q = mcdeltaT
m = mass
c = specific heat of substance
q = heat absorbed or released
Specific Heat
amount of energy required to raise the temperature of one gram of substance by one degree Celsius/Kelvin
Heat capacities
reason why it is less heat to raise temp of glass of water than a pool
= mass * specific heat
Constant Pressure Calorimeter
incident pressure (atmospheric pressure) is e kept constant
temperature is measured as reaction progresses with no gain/loss of heat to the environment
Constant Volume Calorimetry
no work is done as W = p* delta V
no heat is exchanged between the calorimeter and universe so Q calorimeter is 0
deltaUsys + deltaUsurr = deltaU cal = Q - W = 0
delta U sys = - delta U surr
qsys = -qsurroundings
Heating Curves
When a compound is ehated, temperature rises until the melting/boiling point is reached.
Here temp stays constant until all of the sample is converted to the next phase and then temp begins to rise again
When phase changes occur, the heat added does not change the _____ but is used to _____
temperature
overcome the attractive forces holding the phase
Enthalpy of Fusion (latent heat of Fusion)
transition during solid-liquid boundary
determines the heat transferred during phase change
+ when going from solid to liquid as heat is added
- when going from liquid to solid as heat must be removed
Enthalpy of Vaporization (latent heat of vaporization)
transition during liquid-solid boundary
determines the heat transferred during phase change
+ when going fromn liquid to gas as heat is added
- when going from gas to liquid as heat is lost
q = mL
m = mass
L - latent heat, enthalpy essentially of the process
The total amount of heat needed to cross multiple phase boundriesis a _____ of the heats for changing the temperature of each of the respective phases and the heats associated with phase changes.
summation
ex: energy required to make ice cube melt at 40 degrees
q1 = heating to the transition temperature (q=mcdeltaT)
q2 = heat generated during phase change (q=mL)
q3 = heat generated to a temperature(q=mcdeltaT)
Enthalpy Change of a Reaction
deltaH reaction = Hproducts - Hreactants
+ = endothermic process
- = exothermic process
Enthalpy cannot be measured, only _______
deltaH
Standard Enthalpy of Formation (deltaHf)
enthalpy required to produce one mole of a compound from its elements in standard state
Standard Heat of a Reaction (deltaHrxn)
enthalpy change accompanying a reaction being carried out under standard conditions
deltaHrxn = sum( deltaHf,prod ) - sum(deltaHf,react)
Hess’s Law
states that enthalpy changes of reactions are additive
deltaHrxn = deltaH(reactants->elements) + deltaH(elements->products)
remember to add the deltaHrxns together and flip sign if flipping direction of the reaction (even multiply if need to)
arrange to cross out uncessary atoms/elements
Bond Dissociation Energy
average energy required to break a particular type of bond between atoms in the gas phase (endothermic reaction
Bond breaking has the same enthalpy as bond formation but is _____
opposite
Standard Heat of Combustion (delta H combo)
enthalpy change associated with the combustion of a fuel
Second Law of Thermodynamics
energy is spontaneously dispered from being localized to becoming spread out when not hindered
Entropy
how spontaneous the dispersion of energy at a temperature is
deltaS = Qrev/T
Q rev = heat gained/lost in a reversible process
delta S of products and reactants can be used to find deltaSrxn like entropy (products - reactants)
When energy is distributed into a system at a given temperature, its entropy _____ . When energy is distributed out of a system, its entropy _____ .
increases
decreases
Gibbs Free Energy
measure of the change in enthalpy and entropy as a system undergoes a process
tells if a reaction is spontaneous or not
deltaG = deltaH - T*deltaS
T*deltaS represents the total amount of energy absorbed by a system when its entropy increases reversibly
Movement towards the equilibrium position is a _____ in Gibbs Free Energy (G <0) and is ______. The reaction RELEASES energy and is called ________.
Movement away from the equilibrium position is an ____ in Gibbs free energy (G > 0) and is _______. The reaction is ___ and ABSORBS energy.
decrease, spontaneous, exergonic
increase, nonspontaneous, endergonic
At equilibrium, deltaG is ______ and deltaH = T*deltaS
0
delta H delta S \+ + \+ - - + - -
1) spontaneous at HIGH Temperature
2) nonspontaneous always
3) spontaneous always
4) spontaneous at low temperature
Remember, rate of a reaction is dependent on Ea, _______, not delta G
activation energy
When a reaction occurs with a Kinetic and Thermodynamic product, at first the ____ product will be dominant due to the low _____.
Over time, ____ will be apparent because of the low ____.
Kinetic, activation energy
Thermodynamic, gibbs free energy
Free Energy of Reaction
deltaGrxn = deltaGproducts - deltaGreactants
Deriving standard free energy change from equilibrium constant
deltaGrxn = -RT ln Keq
T in kelvins
R is ideal gas constant
greater the value of Keq, the more postive the ln and the more negative the deltaG
Determining Free Energy change for a reaction in Progress
deltaGrxn = deltaGrxn(standard) + RTlnQ = RTln(Q/Keq)
If Q/Keq is less than 1, then free energy will be ______ and ______
If Q/Keq is more than 1, then free energy will be more _____ and _____. If this were the case, the reaction will move in the ____ direction until ______ is reached.
If Q/Keq is = 1, then free energy is ____ and ____ is met.
negative, spontaneous
positive, nonspontaneous
opposite , equilibrium
0, equilibrium
