Chemistry 1 Flashcards
On a pressure vs. volume graph, where is “PV work” done?
The area UNDER the curve
K+MnO42-
What is oxidation state of Mn?
+7
- O= -2 x 4, so -8
- K= +1
∆G=∆H-T∆S
If:
- ΔH is +
- ΔS is +
What is the sign of ∆G?
- ∆H is unfavorable
- ∆S is favorable
∆G is dependent on Temperature!
Will be favorable (-) ONLY if Temp is high enough
- Define “Radiation”
- give an example
Electromagnetic (EM) waves emitted from hot body into surrounding environment
Ex: a black car on a hot day emits heat
HEAT CAPACITY
- Give the formula
C=q/∆T
What does a positive (+) ∆G mean?
Energy is available and the system CAN do work
If slow step is 1st step:
- what can you do wrt the rate law?
the rate law can be written as if it were only 1 step
What 2 formulas relate:
- Keq (equilibrium constant) to ΔG? (Gibbs Free energy )
∆G˚= - RTlnKeq
Keq=e-∆G/RT
The unit “Watt” is the same as?
Joules per second
What should you think of (and mentally replace!) whenever you see the word “TEMPERATURE?”
Temperature=
av. KE of molecules
- 2 L container of water and 4 L container of water
- Compare their heat capacities and SPECIFIC heat capacities
Heat capacity of 4L is twice as much as other
- b/c theres more water available to absorb
Specific heat capacities are the same in both
- because they’re both filled with water
- Entropy (∆S) definition
- units=?
- a measure of disorder in a system
- units=Joules/K
Do catalysts increase % yield?
NOPE!!
How is the sign of work determined in CHEMISTRY?
- Work done ON system= positive
- Work done BY system=Negative
∆Hvaporization definition
- enthalpy value associated with phase change from liquid to gas
- therefore, ∆Hcondensation is the same value, just with a reverse sign)
Chemistry definition for “Work”
a change in volume at a ~P
Catalyst definition
increases rxn rate w/o being consumed in the process
Elements in their elemental state have ∆H˚formation of?
- ZERO
- no ∆ in H needed to create THEMSELVES
Bond broken during rxn=energy ___
required
Writing rate laws: what must you assume? (2)
- assume rxns only proceed FORWARD
- ignore reverse rxn
- only consider the first few seconds of the rxn
- at this time, theres a high [] of each reactant and catalysts (enzymes) present
Thermodynamics includes…(4)
- ΔG
- ΔH
- ΔS
- Keq
- How will the following affect rxn rate?
- increase [products]
NO EFFECT
When heat enters into a system, if the system is capable of volume change, heat can either…
- Do PV work
- Increase temperature (Av KE of molecules)
…or BOTH!!!!!
As far as the MCAT is concerned, ___ is the only thing that changes K
temperature
If, during a rxn, something happens and the Temp increases as a result, what must ∆H be?
- (-)
- aka exothermic
Calculating E˚ for electrochemical rxns
- add together 1/2 rxns
- but when calculating E˚, do NOT multiply by coefficients in balanced rxn
- This is UNLIKE when you calculate ∆Hrxn by adding then multiplying BDE values by the coefficients
∆Hfusion definition
- enthalpy value associated with phase change from liquid to solid
- sign reverses for ∆Hmelting
As a rxn proceeds, if ∆S increases (becomes more disordered)….?
- energy will be released
- therefore more energy will be available to do work
- in short: It’s FAVORABLE
Difference b/t spectator ion and catalyst
- spectator ion
- NO EFFECT
- do NOT participate in rxn
- catalyst
- decreases Ea
- ∴ increases rate
- NOT consumed in rxn
- makes it through the rxn without changing.
- Same among products as it is among reactants
- decreases Ea
- If a graph for a reactant is linear at:
- ln[A] vs. time
- slope=-k
- …………it must be?
- What if it isnt linear?
- must be 1st order
- not linear= not first order
- could still be 0th or 2nd order
Don’t confuse standard state with?
STP values!
Large (-) ∆Hformation means what? (2)
- Energy released when bonds are formed is very high
- compound is VERY STABLE
What is a Black Body Radiator?
- Theoretically perfect body that absorbs ALL energy that hits it
- and then re-emits 100% of the energy absorbed
∆Hsolution definition
enthalpy value associated with dissolution of a species into a solution
Zeroth law of thermodynamics definition
- If object A is in thermal equilib with object B,
- nd obj. C is in thermal equilib with obj. B,
- then obj. A and obj. C are **ALSO **in thermal equilibrium
What DO catalysts affect? What DONT they affect?
- DO affect
- rate (by lowering Ea)
- DONT affect
- Keq
- ∆H
- ∆S
- ∆G
- or any other thermodynamic properties
Define Conduction, give an exampleWhat thing is it similar to?
- conduction=molecular collisions carry heat along a current
- ex: pot of boiling watersimilar to current flow through a wire
- ∆Hformation definition
- Exothermic=?
- Endothermic=?
- enthalpy value for formation of a cpd from its elements in their natural state
- Exothermic is **NEGATIVE **(-)
- Endothermic is **POSITIVE **(+)
∆G (-) means?
energy must be added to rxn (i.e. heat must be added to system) to make it proceed
Define heat capacity
amount of energy (in joules or calories) a system must absorb to give a unit change in temperature
[OH][H]What increases in [] when you INCREASE pH?
[OH]
Give an example of ~V heat capacity
system confined by rigid walls
Second law of thermodynamics definition
heat cannot be changed COMPLETELY into work in a cyclical process, and ∆S in an isolated system can never decrease
Higher ∆S=more likely to…
happen spontaneously
What thermodynamic properties are”SPONTANEOUS?” or “FAVORABLE?”
∆G is (-)∆S is (+)∆H is (-)
Differentiate heat capacity “C” and specific heat capacity “c”
Heat capacity is for a system (ex: solution, container holding sol’n, etc.)Specific heat capacity describes energy absorption for ONE individual substance ONLY!
Think of “rate” as…(3 parts)
- a function of how fast the reactant molecules are moving,
- how much KE they have
- height of Ea “hill” that must be overcome to form products
Isothermal definition
~T (~av. KE of molecules)aka NO HEAT EXCHANGE
Name the 2 kinds of calorimeters and their distinguishable properties
1) Coffee cup (~P)2) Bomb (~V)
As a rxn proceeds, if ∆S decreases…?
energy is REQUIRED to create the increased orderliness, and there’ll be exactly that much LESS energy available to do workin short: it’s UNFAVORABLE
High (+) BDE means the cpd is very ___
stable
If Keq > 1, rxn will be…?(if we are starting at standard conditions)
SPONTANEOUS!
(+) ∆S=?
increased randomness, more energy available to do work
How to calculate ORDER of each reactant (using experimental data)
1) Find 2 steps where [reac] in question changed, but ALL OTHERS DID NOT2) Note the factor by which [reac] changed3) note the factor by which RATE changed across those same 2 trials4) Use this to figure out X^Y=Z
Think of ∆H as…units?
energy contained w/in chemical bondsunit= Joules
When comparing trials to write a rate law for a reactant, what should you look for?
Find 2 trials where []’s of reactant A changes, but everything else (like [] of reactant B and temperature) stays the same. Something with the same conditions!
- How will the following affect rxn rate?
- increasing energy of transition state
- decrease rate
- because it INCREASES Ea
if slow step is 2nd, what happens wrt the rate law?
rate law=rate law of the slow stepslow step will include an intermediate as of the reactants
∆G=-RTlnKeqWhat do you need to remember about this formula?
This formula helps find sign of ∆Gremember: ln of a (+) that is 1 is positive**remember the (-) sign in front of RT! If (lnKeq) is positive, that will turn it negative. Negative x positive=negative, therefore ∆G will be (-), & vice versa
Definition of kinetics. How is it measured?
- study of reaction RATE
- measured in terms of how fast reactants DISAPPEAR, by tracking changes in [] of reactants
If 2 objects are in thermal equilibrium, by definition they have what?
The SAME TEMP!
- How will the following affect rxn rate?
- increase [reactants]
increase rate
PV Work formulaWhat do you need for in order to see PV work, and what is a dead giveaway PV work has been done?
PV Work =P∆VNeeds ~P And change in Volume is a dead giveaway
How will the following affect rxn rate? increasing energy of reactants
increase rate (increasing energy of reactants brings it closer to the Ea–easier to get over the “hill”)
Define convectionWhat are 2 examples?
hotter sections of fluid rise, cooler portions sinkEX:Air currents & Convection currents (El Nino)
The ln of and positive (+) numer LESS than 1 is?
negative (-)
For a reaction to occur, what has to happen with regards to collisions?
- Reacs must collide with enough energy to overcome the Ea “hill”
- Reacs must be in correct spatial orientation
What does Keq=1 mean?
rxn is at equilibrium∆G˚=0
How to write rate law for a catalyzed rxn
write rate law in same way as normal, w/ [catalyst] added in as a reactant
Define the first law of thermodynamics
Energy can’t be created nor destroyed
Bomb calorimeter-how to solve-(What DOES and DOESNT it give?)
-solve using q=mc∆T-DOES give change in internal energy (∆U or ∆E) -DOESNT give negative ∆Hbomb calorimeter is at ~V, in a sealed steel container
Which type of calorimeter allows for pv work? Why?
Coffee cup, because it’s at ~P
What do you do to find the “overall order” of a rxn?
Add together the exponents in the rate law
“Standard State” definition
a set of conditions set as a REFERENCE POINT for measuring ∆H, ∆G, and ∆S
More unstable cpds: -∆Hcombustion?
have a HIGHER ∆Hcombustion, release MORE energy when reacted with O2
Slow step=?
rate-determining step
Third law of thermodynamics definition
pure crystalline substances at absolute zero have a ∆S of 0
What are the 3 types of heat exchange?
1) Convection2) Radiation3) Conduction
For ∆H rxn, if you’re given an ∆H value of +1.5, but your water is a reactant instead of a product, what do you do?
Reverse the sign to (-)
Rate Order graphs: Second order
1/[A] vs time is linear, slope = k
If a graph for a reactant is linear at:[A] vs. time, slope=-kit must be? What if it isnt linear?
Zeroth order not linear=not zeroth order, but it could be first or second, etc
in a 2-step rxn, does the yield of the first rxn affect the Keq of the second?
NOPERS
Specific heat capacity definition
describes energy absorption for ONE individual substance
What do exponents in a rate law represent?
the “order” of each reactant
If Keq < 1, rxn will be?
NON-spontaneous∆G˚ is (-)
When calculating ∆Hrxn, what do you need to remember with regards to signs?
bonds FORMED= energy released (-)bonds BROKEN= energy req’d (+)
Entropy increases with increasing…
number of moleculestemperaturevolumemoles of gas
is heat capacity greater for ~V or ~P?
For ~P, because it CAN do pv work as well as temperature work (therefore has more “capacity” that a system with ~V)
∆E=?
q+W
What is a calorimeter?What do we assume about “q?”
a device used to calculate ∆Hassume q = ∆H, which is true at ~P
Bond formed as result of rxn=energy ___
released
Physics definition for “work”
energy transfer via a force
Relationship b/t enzymes & catalysts
Enzyme=biological catalystALL enzymes are catalysts, but not all catalysts are enzymes
What should you remember for the MCAT about thermal equilibrium?
Everything TENDS TO move towards thermal equilibrium with everything else. -objects with higher temperatures will always equilibrate over time with their surroundings, including other objects with which they are in contact
When a solute is mixed in solution, ∆S is always ___. Why?
is always (+)something becomes more disordered dissolved in a solution
∆Hcombustion definitionHigh ∆Hcombustion means what?
enthalpy value for combustion of a cpd w/ O2 to form water and CO2High ∆Hcomb. value=UNSTABLE molecule(low ∆Hcomb.value=stable)
Rate Law equation:X^Y=Z What do X, Y, and Z represent?
X=factor by which [reac] changedY=order of reactantZ=factor by which the rate changed (across the same 2 trials)
Anything to the zeroth power is equal to?
1
∆Hrxn definitionHow do you solve for it? (1 step, 2 things to remember to do)
enthalpy change for a rxn. -Add together enthalpy change values from the table (given) that, when added, produce net rxn for which you are calculating ∆Hrxn-REMEMBER: if rxn proceeds in opposite direction as it would in the net rxn, change its sign! -REMEMBER: You need to multiply the value given in the table by the coefficient in the balanced net rxn (like…if ∆H value from table for H20 is 1.5 but you have 2 moles of water, multiply 1.5 x 2=3)
Which thermodynamic elements are “NON-SPONTANEOUS” or “UNFAVORABLE?”
∆G is (+)∆S is (-)∆H is (+)
(-) ∆S=?
less randomness, less energy available to do work
Rate Order Graphs:Will only be linear when? (2)
1) When rxn only has 1 reactant, or2) when it is part of a multiple reactant rxn where rate is independent of ALL other reactants (basically, when the other reactant is zeroth order or is in excess)
- How will the following affect rxn rate?
- increasing [catalyst]
**INCREASE **rate
the word “decomposition” tells us what?
we are going from ONE species to 2+ species (∆S is positive)
Thermodynamic Formula
∆G=∆H-T∆S
Calculating ∆Hrxn using BDE’s
add up BDE’s in products & reactants-bond broken during rxn= energy REQUIRED, BDE has (+) sign-bond formed as a result of rxn= energy RELEASED, BDE has a (-) sign
How is the sign (+/-) defined in PHYSICS?
When force & displacement are in same direction (ie lifting a box), work is (+)When force & displacement are in opposite direction (ie lowering a box), work is (-)
Think of Gibbs Free Energy, ∆G, as…
the amount of “free” or “useful” energy available to do work (**Note**doesnt include pv work)
How will the following affect rxn rate? increase temp
increases rate
Give an example of ~P heat capacity
water in a beaker (open to the atmosphere)
1˚ C= ___ Kelvin
274 K
When is heat ,q, added exactly proportional to the increase in temperature? Why?
When system is at ~VNo PV work gets done–it 100% of energy added goes towards increasing temperature
When values are given for standard state conditions, what thingy is added?
superscript is added –> ∆H˚ “not”
Collisions cause?
reactions!
Light colors radiate and absorb ___dark colors radiate and absorb ___
Light: absorb lessDark: absorb more
Rate Order graphs: Zeroth order
[A] vs time is linear with slope= -k
What are 2 ways to define the first law of thermodynamics?
1) total energy of an isolated system is constant2) Total energy in a closed system (energy can leave, mass can’t) is equal to the heat,q, absorbed by that system PLUS and work done on that system by its surroundings
Isobaric definition
~P
∆S increases with? (4, plus 1 caveat)
1) increased # of items/particles/molecules**CAVEAT: # moles gas trumps # moles in other phases (cause gas is VERY disordered)…2 mol react with 1 mol (g) product=Positive ∆S2) Increased Volume3) Increased temp (av. KE of molecules)4) Increased DISORDER (ex: amorphous struc more disordered than crystalline) and COMPLEXITY (ex: C2H6 has greated ∆S than CH4)
- How will the following affect rxn rate?
- increase Ea
**DECREASE **rate
If a graph for a reactant is linear at:1/[A] vs time, slope=-kit must be? what if it isnt linear?
it must be 2nd ordernot linear=not 2nd order. could still be 1st or 0th
Rate Order graphs: first order
ln [A] vs time is linear with slope= -k
