Gen chem 7

Question 1

what is a system(hint: 2 defs)?

what is the surroundings?

Answer 1

a system is the matter being observed-its the total amount of reactants and products in a chemical reaction
surroundings is everything outside of the system

Question 2

what are the three different systems and their defs?

Answer 2

isolated: system cannot exchange energy (heat and work) or matter with the surroundings(insulated bomb calorimeter)
closed: system can exchange energy (heat and work) but not matter with the surroundings(steam radiator)
open: system can exchange both energy (heat and work) and matter with the surroundings(pot of boiling water)

Question 3

what is the equation of the first law of TD and what are the meanings of the variables?
what processes occur when a system’s temperature is constant(and what does this imply and why?)

Answer 3

U=Q-WU is the change in internal energy of the system, Q is the heat added to the system, and W is the work done by the system
isothermal processes(this implies that the system's internal energy is also constant, because temp and internal energy is directly proportional)

Question 4

when U is constant, what is the value for the change in U and what does the first law of TD simplify to?
how does the graph of an isothermal expansion look?

Answer 4

when U is constant, delta U=0 and the first law simplifies to Q=W(the heat added to the system equals the work done by the system)
get pic from page 215

Question 5

when do adiabatic processes occur
when Q=0 what does the first law simplify to?
how does the graph of an adiabatic process look?

Answer 5

these processes occur when no heat is exchanged btween the system and the surroundings; thus, the thermal energy of the system is constant thruout the process.
when Q=0, the first law simplifies to U=-W (the change in internal energy of the system is equal to work done on the system([the opposite of work done by the system])
look on page 216 for answer

Question 6

when do isobaric processes occur?
how do isobaric processes affect the first law?
how does an isobaric process appear on a graph and how does the graph look?

Answer 6

when the pressure of the system is constant
isobaric processes do not affect the first law, but remember it appears as a flat line on a P-V graph
(the answer is 216)

Question 7

do isovolumetric/isochoric processes experience a change in volume?
why is no work performed in isovolumetric/isochoric processes?
how does the first law simplify in this case?
how do isovolumetric processes appear on a P-V graph? also what does the area under the curve represent and what is its value?

Answer 7

no they do not
no work is performed because the gas does not expand or compress
the first law of TD simplifies to delta U=Q(the change in internal energy is equal to the heat added to the system)
An isovolumetric/isochoric process appears as a vertical line on a P-V graph; the area under the curve reps the work done by the gas and its value is zero(no work is done)

Question 8

does spontaneity depend on temp?

why are spon reactions rare

Answer 8

YES! reactions can be spon at certain temps, while nonspon at others.
spon reactions are rare because they have very high activation energies.

Question 9

what is a common method for supplying energy for nonspon rxns
what do state functions describe? what cant they describe? what can state functions compare?

Answer 9

you can do this by coupling nonspon rxns to spon rxns
they describe a system in an equilibrium state; they cant describe the process of the system(that is, how the system got to its current equilibrium); they compare equilibrium states

Question 10

what do process functions describe? wat are the two imp ones?

Answer 10

they describe the path taken from one equil state to another, and two imp ones are heat and work

Question 11

What is the mnemonic to help remember all the state functions?

Answer 11

When im under pressure and feeling dense, all i wanna do is watch TV and get HUGS

Pressure(P), density(p), temperature(T), volume(V), enthalpy(H), internal energy(U), Gibbs free energy(G) and entropy(S).

Question 12

How is standard conditions different than standard temp and pressure?

what are the values for both std conditions and std temp and pressure?

Answer 12

standard conditions are used for kinetics, equil, and TD problems; standard temp and pressure are used for ideal gas calculations

std conditions: 25C(298 K), 1 atm pressure, 1 M concs
standard temp and pressure 0C(273 K), and pressure is 1 atm

Question 13

what does the degree sign stand for in delta G(standard gibbs free energy), standard entropy(delta S) and standard enthalpy (delta H)

Answer 13

the degree sign in these variables reps zero, as the standard state is used as the zero point for all TD calculations

Question 14

for what kind of systems does a phase diagram show the standard and nonstandard states of matter for a given substance

Answer 14

isolated system

Question 15

what happens to the rates of the forward and reverse reactions when at equilibrium?

Answer 15

they will be the same

Question 16

what happens to temp when a liquid loses a high energy particle
what kind of thermal process is evaporation(what is evaporation also called?); what is the heat source

Answer 16

the temp of the rest of the liquid goes down
endothermic
evap is also called vaorization; the heat source is the liquid water(or sometimes it could be the one receiving thermal energy)

Question 17

what kind of process is boiling?
what is condensation facilitated by?
describe the meaning of vapor pressure of a liquid?
why does vapor pressure go up as temp goes up?

Answer 17

it is also a vaporization process
by a higher pressure or lower temp
the vapor pressure of a liquid is the pressure that the gas exerts over the liquid at equil
vapor pressure goes up as temp goes up becuz more moles have sufficient energy to escape into the gas phase

Question 18

describe what boiling point means

as temp of the solid goes up what happens to the availability of microstates

Answer 18

the boiling point is the temp at which the vapor pressure of the liquid equals the ambient (also known as applied, external or incident )pressure
the availability of microstates goes up too

Question 19

from solid to gas phase is?
from gas to solid is?
KNOW THE PHASE DIAGRAM ON PAGE 222
on a phase diagram, where is the gas phase found?
what is the triple point?(two answers)

Answer 19

sublimation
deposition
gas phase found at high temps and low pressures
solid phase found at low temps and high pressures
liquid phase found at moderate temps and moderate pressures
triple point is where the three phase boundaries meet and where they exist in equilibrium

Question 20

describe the phase boundary that separates the solid and liq phases vs the one that separates the gas and liq phases(and how does the crit point relate to this?)
what is the heat of vaporization at the crit point and at all temps and pressures beyond this point?

Answer 20

the phase boundary that separates the liq and solid phases extends indefinitely from the triple point but the phase boundary between the gas and liq phases terminates at the crit point
as a liq is heated in a closed system, its density goes up and the density of the vapor sitting above it goes up too(at the crit point, these two densities become equal AND there is no distinction btween the phases; the heat of vaporization at the crit point and for ALL temps and pressures above the crit point values is zero

Question 21

what does the zeroth law of TD imply?
what kind of function is heat?
what does the first law of TD state(and what is the eqn?)
what is the conversion unit for calories and joules?
what assumption does the mcat make for TD problems under constant pressure in regards to enthalpy and heat?

Answer 21

this law implies that objects are in thermal equilibrium only when their temps are equal
heat is a process function
the first law of TD states that the change in the total internal energy of a system is equal to the amount of heat transferred to the system minus the amount of work done by the system(delta U= Q-W)
the conversion rate btween calories and joules is 1 cal=4184 J
the mcat assumes that enthalpy and heat are equivalent under constant pressure

Question 22

what are the two basic types of calorimetry and what kind does coffee cup calorimetry apply to? how about bomb calorimetry?
what does the q=MCAT eqn show?
define specific heat
what is the specific heat of water?
how do you find the heat capacity?

Answer 22

constant pressure and constant volume calorimetry
coffee cup calorimetry is constant pressure calorimetry
bomb calorimetry is constant volume calorimetry
the q=MCAT eqn shows how heat is absorbed or released in a given process
specific heat is the energy that it takes to raise the temp of one gram of a substance by one degree C or one Kelvin
1 cal/g.K= specific heat of water
heat capacity= mass x specific heat

Question 23

what happens to incident pressure or atm pressure in a constant pressure calorimeter?
in regards to a constant volume calorimeter/bomb calorimeter, what happens to work in an isovolumetric process and thus for the calorimeter?
why is the whole calorimeter considered isolated from the rest of the universe, so what, in regards to this example, can we identify as the system and the surr?

Answer 23

it stays constant
in regards to a constant volume calorimeter/bomb calorimeter, there is no work done in an isovolumetric process(W=PdeltaV = 0), so therefore the work of the calorimeter is 0)
the whole calorimeter is considered isolated from the rest of the universe becuz of the insulation; in this example, the system is the sample plus the oxygen and steel vessel AND the surr is the water

Question 24

no heat is exchanged btween the calorimeter and the universe so what is the value for q? and what is the relation that reinforces this? and what relation does this lead to?
and becuz no work is done, what relation is derived?

Answer 24

q is 0
deltaSystem + Usurroundings = deltaUcalorimeter =Qcalorimeter - Wcalorimeter =0
deltaUsystem=-deltaUsurroundings

since no work is done» qsystem=-qsurroundings

Question 25

by using the insulation layer to isolate the entire calorimeter from the rest of the universe, what did we create?
what heat was exchanged and not exchanged in this system?
what does heat exchange btween the system and its surroundings make it possible to do?

Answer 25

by using the insulation layer to isolate the entire calorimeter from the rest of the universe, we created an adiabatic process
no heat is exchanged btween the calorimeter and the rest of the universe, but it is exchanged btween the steel decomposition vessel and the surrounding water

heat exchange btween the system and its surroundings makes it possible to calc the heat of combustion

Question 26

when a compound is heated, the temp rises until what point? then what happens to the temp? then what happens when the entire sample is converted

Answer 26

when a cmpd is heated, the temp rises until the melting or boiling point is reached. then the temp remains constant as the cmpd is converted to the next phase. once the entire sample is converted, then the temp begins to rise again

Question 27

how should we think about equilibrium questions regarding the final temp of a two-liquid (or liquid-solid) system? and knowing this, how should we set up an equation?

Answer 27

we must remember that the colder object gains thermal energy and the hotter object loses thermal energy
qcold=-qhot

Question 28

why cant q=mcat be used during phase changes?
what happens to energy as a solid turns to a liquid?
what happens to temp when we remove heat from a liquid at the solid liquid phase transition?

Answer 28

we cannot because there are no changes in temp during phase changes, T=0
the solid will absorb energy which allows particles to overcome the attractive forces holding them in a rigid struc
the temp will cause the formation of a rigid lattice of water molecules

Question 29

during phase changes, what values do we use?
when transitioning at the solid liquid boundary, what must be used to determine the heat transferred during the phase change?
when transitioning from solid to liquid, what happens to the change in enthalpy? liquid to solid?
when transitioning at the liquid-gas boundary, what must be used to determine the heat transferred during the phase change(and what happens to its sign convention?

Answer 29

enthalpy values
enthalpy or heat of fusion must be used
the change in enthalpy will be positive because heat must be added; the change in enthalpy will be negative becuz heat must be removed
enthalpy or heat of vaporization must be used(and it follows the sign pattern above)

Question 30

what eqn do we use when deltaT is 0(and what do the variables stand for)? and if we used q=mcat, what would we erroneously believe?
how do we find the total amt of heat needed to cross multiple phase boundaries?
****STUDY AND KNOW THE HEATING CURVE FOR A SINGLE COMPOUND ON PAGE 228

Answer 30

we use q=ml q is heat, m is mass and L is the latent heat(which is a term for the thermal energy in an isothermal process, given in the units cal/g)
we would erroneously believe that q=0
it is simply a summation of the heats for changing the temperature of each of the respective phases and the heats associated with phase changes.

Question 31

FORMULA FOR HRXN
what kind of function is enthalpy
sign for enthalpy in endothermic/exothermic rxns

Answer 31

delta Hrxn= Hproducts - Hreactants
state function
+/-

Question 32

what is the standard enthalpy of formation(delta degree Hf)?
what does standard state refer to?
what is the standard state of enthalpy for an element in its standard state?

Answer 32

it is the enthalpy req’d to make one mole of a compound from its elements in their standard states
standard state refers to the most stable physical state of an element or compound at 298 K and 1 atm
it is 0

Question 33

what is the standard enthalpy of a reaction?
how can it be calc’d?
because enthalpy is a state function and a property of the equilibrium state, what can we say about the pathway? what does hess’s law state about enthalpy changes of reaction?

Answer 33

the enthalpy change accompanying a rxn being carried out under standard conditions.
this can be calc’d by taking the difference btween the sum of the standard heats of formation for the products and the sum of the standard heats of formation of the reactants(delta degreeHrxn= Edelta degree Hfprods - Edelta degree Hfreactants

the pathway is irrelevant to the change in enthalpy from one equilibrium state to another. becuz of this, these enthalpy changes are additive(deltaH = deltaH1 + deltaH2 + deltaH3

Question 34

the enthalpy change for the reverse of any reaction has the same what but opposite what?

Answer 34

same magnitude, opposite sign

Question 35

for a liquid to gas phase change, what will the hrxn always equal (as long as the initial and final states exist at standard conditions)?
state functions are always what independent
you can use hess’s law for what function, including what and what
what is bond dissociation energy(what kind of process is bond dissociation energy)? what are the units?

Answer 35

hxrn will always equal hvap in this case, regardles of the path it takes
state functions are path independent
state function; gibbs free energy and entropy

it is the average energy req’d to break a particular bond between atoms in the gas phase; this is an endothermic process; kJ/mol of bonds broken

Question 36

what bond breaking positive but bond formation negative?

give the eqn for an enthalpy change associated with a reaction is given by:

Answer 36

bond formation has the same magnitude as bond breaking but the sign is negative because during bond formation energy is released when bonds are formed

delta degreeHrxn= E deltaHbonds broken - E deltaHbonds formed = total energy absorbed - total energy released

Question 37

bond breaking is whatthermic; bond formation is whatthermic
most combustion reactions on the mcat occur in the presence of what, but what is not always the what
what biochemical rxn is also a combustion reaction? what is the fuel and what is the oxidant?

the second law of TD states wat?

Answer 37

endothermic/exothermic
atm oxygen, oxygen; oxidant
glycolytic pathway; fuel is glucose, oxidant is oxygen(and overall rxn yields CO2 and water)
-it states that energy spontaneously goes from being localized to being spread out(if not hindered from doing so)

Question 38

define entropy
eqn and variable defs?
does entropy go up or down during freezing a liquid? from liquid to gas?
for any substance, what will be the phase transition with the greatest increase in entropy?
units for entropy?
when energy is distributed into a system at a given temp, the entropy does what?
when energy is distributed out of a system at a given temp, the entropy does what?
what is the second Law of TD considered as and why?

Answer 38

entropy is a measure of the spontaneous dispersal of energy at a specific temp
deltaS= Qrev/T
Qrev= heat that is gained or lost in a reversible process, T is temp in Kelvin
goes down because liquid becomes a more ordered solid; goes up becuz liquid becomes a much more disordered gas
J/mol K
entropy goes up; entropy goes down
the seocnd law of TD is considered time’s arrow becuz there is a unidirectional limit on the movement of energy by which we recognize before and after.

Question 39

how to find the standard entropy change for a reaction, delta degree Srxn?

Answer 39

this can be calculated using the standard entropies of the reactants and products
delta degree Srxn= EdeltaSproducts -EdeltaSreactants

Question 40

the change in free energy is what?
what is the eqn for the change in free energy?
cool mnemonic for this equation?

Answer 40

the change in free energy is the max amount of energy released by a process occurring at constant temp and pressure that is available to perform useful work.
deltaG = deltaH - TdeltaS
Goldfish are (equals sign) Horrible without(minus sign) Tartar Sauce

Question 41

how do chemical reactions proceed with regard to free energy?

Answer 41

they will proceed in whatever direction lets them have a reduction in free energy

Question 42

what indicates that a rxn is spon?

Answer 42

a decrease in free energy

Question 43

what term is endo/exothermic used to describe?
what term is endo/exogonic used to describe?
are exergonic rxns spon?

Answer 43

enthalpy
Gibbs free energy
yes they are spon

Question 44

EFFECTS OF H S AND T ON SPONTANEITY
Enthalpy and Entropy:
\+ +
\+-
-+
--
when is G temp dependent?

Answer 44

spon at high T
nonspon at all T
Spon at all T
Spon at low T
it is temp dependent when H and S have the same sign

Question 45

what type of process is boiling water? what sign does H, S and TdeltaS have?
what does the rate of a rxn depend on, G or Ea?
for the period of time after a rxn begins, why will the major product be the one that is produced more quickly(and what type of control is the rxn under at this point?)
However, eventually what will be the dominant product and why(then what control is this reaction under at this point?)

Answer 45

endothermic; H, s and TdeltaS is positive
it depends on Ea
this is becuz of lower Ea; the rxn is said to be under kinetic control will be the thermodynamically more stable product becuz of lower G; the rxn is said to be under thermodynamic control

Question 46

what can we say about the concs of any solutions during standard free energy determinations
what is the standard free energy of formation of a compound?
what is the standard free energy of formation for any element under standard state conditions
what is the standard free energy of a reaction(and that is….)
how can the free energy of the reaction be calc’d?

Answer 46

the concs are all 1 M
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
Zero
it is the free energy change that occurs when that reaction is carried out under standard state conditions(and that is when the reactants are converted to the products at standard conditions of temp(298 K) and pressure(1 atm).
just like entropy and enthalpy, the free energy of the reaction can be calc’d from the free energies of formation of the products and reactants(deltaGdegreerxn= EdeltaGdegreefprods - EdeltaGdegreefreacs

Question 47

what is the eqn for standard free energy change for a reaction from the equilibrium constant Keq?
how does a larger value for Keq affect the natural log? and how does this then affect the standard free energy change? and how does this then affect spontaneity of the rxn?
what happens once a rxn starts in regards to standard state conditions(specifically what)? what must be replaced

Answer 47

deltaGdegreerxn = -RT ln Keq
R is ideal gas constant, T is temp in K, Keq is the equil constant
the larger value for Keq means that ln will be more positive as well
the more positive the ln, the more negative the standard free energy change
the more negative the standard free energy change, the more spon the rxn will be
once the rxn starts, standard state conditions no longer apply(specifically 1 M solutions)
the value of the equilibrium constant must be replaced with another number that is reflective of where the reaction is in its path toward equilibrium

Question 48

how do we find the free energy change for a reaction that is in progress(what do we relate(start answer off like that) and what is the eqn?
shortcuts for the eqn regarding Q/Keq, ln and G
if Q/Keq is less than 1, greater than 1 and equal to 1?
what does Q stand for and what does its use signify?

Answer 48

we relate Grxn not Gdegreerxn
deltaGrxn= deltaGrxn standard + RT ln Q = RT ln Q/Keq
if Q/Keq is less than 1, the ln will be negative and the delta G will be negative, so rxn proceeds forward spon’ly until equil is reached
if Q/Keq is greater than 1, the ln will be positive and the delta G will be positive, so rxn spon’ly proceeds in the reverse direction until equilibrium is reached
if Q/Keq is equal to 1, the reaction quotient is equal to the Keq, and the free energy change is 0(ln 1= 0)
Q is the reaction quotient and its use signifies that the reaction IS NOT at equilibrium.