Thermochemistry Flashcards
What are isolated systems?
they exchange neither matter nor energy with the environment.
What are closed systems?
They exchange energy, but not matter with the environment.
What are open systems?
they exchange both energy and matter with the environment.
What are Isothermal processes?
They are processes that occur at a constant temperature
What are adiabatic processes?
exchange no heat with the environment.
What are Isobaric processes?
occur at a constant
What are isovolumetric (isochoric) processes?
occur at a constant volume
What are state functions?
describe the physical properties of an equilibrium state; they are a pathway independent and include pressure, density, temperature, volume, enthalpy, internal energy, Gibbs free energy, and entropy.
What are standard conditions?
defined as 298K, 1 atm, and 11 M concentrations. Used for kinetics, equilibrium, and thermodynamics. Do not confuse with (STP) standard temperature and pressure for gas laws.
What is the standard state of an element?
it is the most prevalent form under standard conditions; standard enthalpy, standard entropy, and standard free energy
What is fusion (melting) and freezing (crystallization or solidification)?
A phase change that occurs at the boundary between the solid and the liquid phases.
What is vaporization (boiling or evaporation)?
occurs at the boundary between the liquid and the gas phases
What is sublimation and deposition?
occurs at the boundary between the solid and gas phases
What is the critical point?
a temp past this, the liquid and gas phases are indistinguishable.
What is the triple point?
at this point all three phases of matter exist in equilibrium
What is a phase diagram?
fro a system graphs the phases and phase equilibria as a function of temperature and pressure.
What is temperature?
scaled measure of the average kinetic energy of a substance.
What is heat?
The transfer of energy that results form difference of temperature between two substances.
What is Enthalpy?
it is the measure of the potential energy of a system found in the intermolecular attractions and chemical bonds
What is Hess’s law?
states that the total change in potential energy of a system is equal to the changes of potential energies of the individual steps of the process.
How can enthalpy be calculated?
using heat formations, heats of combustion, or bond association.
What is entropy?
while often thought of as disorder, is a measure of the degree to which energy has been spread throughout a system or between a system and its surroundings. Entropy is a ratio of heat transferred per mole per unit kelvin. Entropy is maximized at equilibrium.
What is Gibbs free energy?
it is derived from both enthalpy and entropy values for a given system. The change in Gibbs free energy determines whether a process is spontaneous or not.
What is Gibbs free energy dependent on?
temperature; temp dependent processes, change between spontaneous and non-spontaneous, depending on the temperature.
First law of thermodynamics equation
ΔU= Q-W . U is the change in internal energy, Q is heat added, and W is work done by system.
Heat transfer (no change) eq
q = mcΔT m is mass, c is specific heat, and T is change in temp. when thinking of heat think which one is receiving heat and losing heat.
heat transfer (during phase change)
q=mL . m is mass L is latent heat, a general term for the enthalpy of a isothermal process .
Generalized enthalpy of reaction
ΔHrxn = H products - H reactants
standard enthalpy of a reaction
ΔH’rxn = ΣΔH’f products - ΣΔH’f, reactants
Bond enthalpy
ΔH’rxn = ΣΔH bonds broken- ΣΔH bonds formed
Entropy
ΔS = Qrev/T . Qrev is the heat that is gained or lost in a reversible process
Second law of thermodynamics
ΔS universe = ΔSsystem + ΔSsurroundings >0
Gibbs free energy
ΔG=ΔH- TΔS
Standard Gibbs free energy
ΔG’rxn =ΣΔG’f,products - ΣΔG’f,reactants
Standard Gibbs free energy from equilibrium constant
ΔG’rxn = -RTln Keq
Gibbs free energy from reaction quotient
ΔGrxn= ΔG’rxn +RT ln Q= RT ln Q/Keq
Temp and internal energy are..?
directly proportional .
PV=
nRT
How can energy be supplied to a non-spontaneous reaction?
by coupling non-spontaneous reaction to spontaneous ones.
What is calorimetry?
The process of measuring transferred heat .
What is the zeroth law of thermodynamics?
objects that are in thermal equilibrium only when their temperatures are equal.
Specific heat is what?
defined as the amount of energy required to raise the temperature of one gram of a substance by 1 kelvin or degree Celsius.
heat capacity
=mc
Calorimeter equation
q system= -q surroundings mct system= mct surrounding
Calculating the the phase changes of ice to gas
calculate the heat transfer and the phase changing steps, each step will give a certain amount of energy and the add them all together. Use 1= mcT and q=mL
What is bond dissociation energy?
the average energy that is required to break a particular type of bond between atoms in the gas phase, and is an endothermic process.
What are some combustion reactions?
with oxygen, diatomic fluoride, and Hydrogen.
How does ΔS and ΔH affect ΔG?
ΔG= ΔH-TΔS
if both are positive G is spont at high temp .
if H is positive and S is neg than it is nonspont at all T
If H is negative and S is positive it is spont at all T
If H is negative and S is negative is spont at low temp .
Rate of reaction depends on…
Ea (activation energy), not G
