Chem #7 Flashcards
system
the matter that is being observed—the total amount of reactants and products in a chemical reaction.
surroundings
Surroundings (environment): everything outside of the system
isolated system
The system cannot exchange energy (heat and work) or matter with the surroundings; for example, an insulated bomb calorimeter.
closed system
the system can exchange energy (heat and work) but not matter with the surroundings; for example, a steam radiator.
open system
the system can exchange both energy (heat and work) and matter with the surroundings; for example, a pot of boiling water
process
when a system experiences a change in one or more of its properties (such as concentrations of reactants or products, temperature, or pressure)
isothermal process
occur when the system’s temperature is constant
Constant temperature implies that the total energy of the system (U) is constant (delta U = 0).
adiabatic process
occur when no heat is exchanged between the system and the environment.
isobaric process
occur when the pressure of the system is constant.
Does not alter the first law but appears as a straight line on the P-V graph.
isochoric
experience no change in volume
Vertical line on the P-V graph, work = 0.
spontaneous process
one that can occur by itself without having to be driven by energy from an outside source.
Spontaneous processes can sometimes be VERY slow.
coupling
a common method for supplying energy for nonspontaneous reactions.
• Ex: The combustion of glucose is exergonic; the formation of peptide bonds is endergonic. Energy from combustion of glucose can be stored in the bonds in GTP, which are then lysed to provide the energy for forming peptide bonds.
state functions
describe the system in an equilibrium state. They cannot describe the process of the system. Useful for comparing one equilibrium state to another.
o Pressure, density, temperature, volume, enthalpy, internal energy, Gibbs free energy, entropy
o Independent of the path (process) taken, but are not necessarily independent of each other
process functions
the pathway taken from one equilibrium state to another o Work (W) and heat (Q) are the most important ones.
state functions only depend on _____
the differences between the final and initial states, not how you get there.
standard conditions
defined because systems can be in different equilibrium states at different temperatures and pressure (for measuring the enthalpy, entropy, and Gibbs free energy changes in a reaction).
o 298 K, 1 atm pressure, 1 M concentrations.
o Used for kinetics, equilibrium, and thermodynamics.
standard conditions versus standard temperature and pressure (STP)
STP used for ideal gas law and is 273 K, 1 atm
standard conditions is 298 K, 1 atm, 1 M, and is used for kinetics, equilibrium, and thermodynamics.
standard state
the most stable form of a substance.
Standard enthalpy, standard entropy, and standard free energy changes
the changes that occur when a reaction takes place under standard conditions
process going solid to liquid
melting, fusion
process going liquid to gas
evaporation, vaporization
: when some of the liquid molecules near the surface have enough kinetic energy to leave the liquid phase and escape into the gaseous phase.
• Endothermic process for which the heat source is the liquid water.
• Each time the liquid loses a high-energy particle, the temperature of the remaining liquid decreases.
process going gas to liquid
condensation
: gases returning to the liquid phase.
• Facilitated by lower pressure or higher temperature.
• Vapor pressure of the liquid: the pressure that the gas exerts over the liquid at equilibrium.
• Boiling point: the temperature at which the vapor pressure of the liquid equals the ambient (external, applied, or incident) pressure
process going liquid to solid
freezing/solidification/crystallization
process going gas to solid
deposition
process going solid to gas
sublimation
what is occuring during sweating
sweating (vaporization) is an endothermic reaction as energy is required for liquid to vaporize into gas which removes heat from the body
blood vessels vasodilate to get more heat release.
phase diagrams
graphs that show the standard and nonstandard states of matter for a given substance in an isolated system, as determined by temperatures and pressures.
Graphs that show the temperatures and pressures at which a substance will be thermodynamically stable in a particular phase.
• Also show temps and pressures at which phases will be in equilibrium.
triple point
all 3 phases are in
equilibrium
the point at which the three phase boundaries meet. The temperature and pressure at which the three phases exist in equilibrium.
critical point
where the phase boundary between the gas and liquid phases terminates.
• This is the temperature and pressure at which there is no distinction between the phases.
o Supercritical fluids
o The heat of vaporization at this point and for all temperatures and pressures above the critical point is zero.
ABOVE WHICH THE HEAT OF VAPORIZATION IS 0
phase changes
: (solid = liquid = gas) are reversible, and an equilibrium of phases will eventually be reached at any given combination of temperature and pressure.
Ice to water and water to ice at the same time.
Phase equilibria: analogous to dynamic equilibria of reversible chemical reactions (concentrations remain the same because the forward and reverse reactions are equal).
The temperature of any substance in any phase is related to the _____ of the molecules that make up the substance.
average kinetic energy
boiling point
a specific type of vaporization that occurs only under certain conditions. Boiling is the rapid bubbling of the entire liquid with rapid release of the liquid as gas particles.
Only occurs above the boiling point of the liquid and involves vaporization through the entire volume of the liquid.
the temperature at which the vapor pressure of the liquid equals the ambient (external, applied, incident) pressure
what point does the boiling point occur at?
the temperature at which the vapor pressure of the liquid equals the ambient (external, applied, or incident) pressure
The availability of energy _____ (specific way in which the energy of a system can be organized) increases as the temperature of the solid increases.
microstates
draw a graph representing heat added and temperature
plateaus and inclines
plateau is a phase change
temperature
related to the average kinetic energy of particle of a substance.
The average kinetic energy of the particles in a substance is related to the thermal energy (Enthalpy) of the substance.
heat
a specific form of energy that can enter or leave a system. The transfer of energy from one substance to another as a result of their differences in temperature.
Zeroth law of thermodynamics: objects are in thermal equilibrium only when their temperatures are equal.
Process function
sign for a system absorbing heat
+
sign for a system releasing heat
_
exothermic
the system releases heat
endothermic
the system absorbs heat
under constant pressure, relate q and enthalpy
equal
calorimetry
the process of measuring transferred heat
calorimetry: constant pressure
coffee cup calorimeter
Imagine a coffee cup that is sealed and there is reduced loss of heat to the environment. The temperature can be measured as the reaction progresses. The constant pressure is atmospheric pressure.
calorimetry: constant volume
bomb calorimeter (decomposition vessel) Sample in oxygen container submerged in water. Wcalorimeter = 0.
bomb calorimeter
constant volume
coffee cup calorimeter
constant pressure
specific heat
the amount of energy required to raise the temperature of one gram of a substance by one degree Celsius (or K)
o Of H2O (l): 1 cal / (g)(K)
o Heat capacity: mass x specific heat
relate specific heat and heat capacity
mass x specific heat = heat capacity
discuss a heating curve
o Compound is heated to melting or boiling point, stays here a little until all of the sample changes phase, then the temperature will begin to rise again.
o When transitioning at the solid-liquid boundary, the enthalpy of fusion (ΔHfus) must be used.
Solid to liquid: it is positive cause heat must be added
o When transitioning at the liquid-gas boundary, the enthalpy of vaporization (ΔHvap) must be used
Liquid to gas: it is positive cause heat must be added
o Latent heat: enthalpy of an isothermal process
o Add up the heats for different steps.
can you have heat being added to an isothermal process?
YES
phase boundary and latent heat on heating curve
enthalpy
(H): used to express heat changes at constant pressure.
o State function
o Change in enthalpy is equal to the heat transferred into or out of the system at constant pressure
o Only ΔH can be calculated, not regular H.
standard enthalpy of formation
formation (ΔH°f): enthalpy required to produce one mole of a compound from its elements in their standard states.
o Standard state is 298 L and 1 atm.
o ΔH°f of an element in its standard state is 0.
Standard enthalpy of reaction (ΔH°rxn):
the enthalpy change accompanying a reaction being carried out under standard conditions.
o Sum of product standard heats of formation minus reactant standard heats of formation
Hess’s law
the enthalpy changes of reactions are additive.
o Enthalpy is a state function so as long as you go from reactants to products it does not matter how you get there, the enthalpy change will still be the same.
o Applies to ANY state function, path independent.
Bond formation is typically ____while bond breaking is typically _____
exothermic
endothermic
Exceptions in biology: ATP: bond breaking is exothermic
Bond enthalpies (bond dissociation energies):
the average energy that is required to break a particular type of bond between atoms in the gas phase. (kJ/mol of bonds broken)
• Does not matter if an element is in its standard state here or not, still add up all of the bond energies.
standard heat of combustion
the enthalpy change associated with the combustion of a fuel. • Typical combustion reactions: o Hydrocarbon with H2 o H2g and Cl2g HClg o F2 is the oxidant
second law of thermodynamics
energy spontaneously disperse from being localized to becoming spread out if it is not hindered from doing so.
o The entropy of the universe is increasing.
entropy
the measure of the spontaneous dispersal of energy at a specific temperature: how much energy is spread out and how widely is it spread out.
o When energy is distributed into a system, its entropy increases.
o Pathway independent.
o + entropy, more disorder.
o Heat pack on a wound dispersal of energy
when is deltaG temperature dependent?
ΔG is temperature dependent when ΔH and ΔS have the same sign.
standard free energy ΔG°rxn
): the free energy change of reactions can be measured under standard state conditions.
o ΔG°f: the standard free energy of formation of a compound is the free energy change that occurs when 1 mole of a compound in its standard state is produced from its respective elements in their standard states under standard state conditions.
Any element is 0.
what is the first law of thermodynamics and how are things defined?
deltaU = q + w
q and w are heat and work done on the system, respectively.
condensation is facilitated by a ___ temperature or a ____ pressure
low
high
vapor pressure is _____
the pressure that a gas exerts over a liquid at equilibrium (it is the vapor pressure OF THE LIQUID)
process of going solid to liquid
melting or fusion
the solid phase of a substance is often found at ____ temperatures and ____ pressures
low
high
the base boundary that separates the solid and liquid _____ while the phase boundary that separates the liquid and gas _____
extends forever
terminates at the critical point
a negative slope in a phase diagram for the liquid and solid boundary means that ____
the liquid is more dense than the solid
increasing pressure with constant temperature results in melting.
____ is a specific form of energy that can leave or enter a system while ____ is a measure of the average kinetic energy of the particles in a system
heat
temperature
1 cal = ___ J
4.184 J
Enthalpy is equivalent to heat under constant ____
pressure
what is another word for bomb calorimeter
decomposition vessel
on a heating curve, you use the _____ when transitioning from solid to liquid (or vice versa) and you use _____ when transitioning from liquid to gas (and vice versa)
enthalpy/heat of fusion
enthalpy/heat of vaporization
what is latent heat used for and what is its units
used for calculating heat added in an isothermal process (heat curve)
units: cal/g
what are the heat capacities for water (solid, liquid, gas)
s: 2.18 J/gK
l: 4.18 J/gK
g: 2 J/gK
a coffee cup calorimeter is exposed to constant pressure from what
the environment
the standard enthalpy of formation of an element in its standard state is ____
0
As compared to Keq values, in Hesses law you can ______ enthalpies
add, multiply by coefficients, negative if reverse (same for entropy and Gibbs free energy)
for K values in equilibrium you multiply them for combining reactions, raise to the power for adding coefficients, and take inverse if doing reverse reaction.
bond breaking is ____ while bond forming is _____
endothermic
exothermic
Can combustion reactions occur without O2?
Yes, Ex: Fluorine as oxidant
what are the units of entropy?
J/(mol)(K)
the energy of the universe _____ reduced spontaneously
can never be
the change in free energy is the _______ released by a process, occurring at _______, that is available to perform ______
maximum amount of energy
constant temperature and pressure
useful work
deltaG is temperature dependent when deltaS and delta H ____
have the same sign
when water’s vapor pressure equals the ambient pressure, this is known as the ____
boiling point
entropy is maximized at _____
equilibrium
longer hydrocarbon chains yield ____ amounts of combustion products and release ___ heat
greater
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