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Flashcards in Chemistry 1 Deck (122):
1

On a pressure vs. volume graph, where is "PV work" done?

The area UNDER the curve

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1

K+MnO​42-

What is oxidation state of Mn?

+7

  • O= -2 x 4, so -8
  • K= +1

2

∆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

3

  • 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

4

HEAT CAPACITY

  • Give the formula

C=q/∆T

5

What does a positive (+) ∆G mean?

Energy is available and the system CAN do work

6

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

6

What 2 formulas relate:

  •  Keq  (equilibrium constant) to ΔG? (Gibbs Free energy )

∆G˚= - RTlnKeq

 

Keq=e-∆G/RT

6

The unit "Watt" is the same as?

Joules per second

7

What should you think of (and mentally replace!) whenever you see the word "TEMPERATURE?"

Temperature=

av. KE of molecules

8

  • 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

8

  • Entropy (∆S) definition
    • units=?

  • a measure of disorder in a system
  • units=Joules/K

9

Do catalysts increase % yield?

NOPE!!

9

How is the sign of work determined in CHEMISTRY?

  • Work done ON system= positive
  • Work done BY system=Negative

10

∆Hvaporization definition

  • enthalpy value associated with phase change from liquid to gas
    • therefore, ∆Hcondensation is the same value, just with a reverse sign)

11

Chemistry definition for "Work"

a change in volume at a ~P

12

Catalyst definition

increases rxn rate w/o being consumed in the process

12

Elements in their elemental state have ∆H˚formation of?

  • ZERO
    • no ∆ in H needed to create THEMSELVES

13

Bond broken during rxn=energy ___

required

15

Writing rate laws: what must you assume? (2)

  1. assume rxns only proceed FORWARD
    • ​​ignore reverse rxn
  2. only consider the first few seconds of the rxn
    • at this time, theres a high [ ] of each reactant and catalysts (enzymes) present

16

Thermodynamics includes...(4)

  1. ΔG
  2. ΔH
  3. ΔS
  4. Keq

17

  • How will the following affect rxn rate?
    • increase [products]

NO EFFECT

18

When heat enters into a system, if the system is capable of volume change, heat can either...

  1. Do PV work
  2. Increase temperature (Av KE of molecules)


    ...or BOTH!!!!!

19

As far as the MCAT is concerned, ___ is the only thing that changes K

temperature

20

If, during a rxn, something happens and the Temp increases as a result, what must ∆H be?

  • (-)
    • aka exothermic

21

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

21

∆Hfusion definition

  • enthalpy value associated with phase change from liquid to solid
    • sign reverses for ∆Hmelting

21

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

21

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

22

  • 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

23

Don't confuse standard state with?

STP values!

24

Large (-) ∆Hformation means what? (2)

  • Energy released when bonds are formed is very high
  • compound is VERY STABLE

25

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

26

∆Hsolution definition

enthalpy value associated with dissolution of a species into a solution

27

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

28

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

29

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

29

  • ∆Hformation definition
    • Exothermic=?
    • Endothermic=?

  • enthalpy value for formation of a cpd from its elements in their natural state
  • Exothermic is NEGATIVE (-)
  • Endothermic is POSITIVE (+)

30

∆G (-) means?

energy must be added to rxn (i.e. heat must be added to system) to make it proceed

31

Define heat capacity

amount of energy (in joules or calories) a system must absorb to give a unit change in temperature

32

[OH][H]What increases in [ ] when you INCREASE pH?

[OH]

34

Give an example of ~V heat capacity

system confined by rigid walls

35

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

36

Higher ∆S=more likely to...

happen spontaneously

36

What thermodynamic properties are"SPONTANEOUS?" or "FAVORABLE?"

∆G is (-)∆S is (+)∆H is (-)

38

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!

39

Think of "rate" as...(3 parts)

  1. a function of how fast the reactant molecules are moving,
  2. how much KE they have
  3. height of Ea "hill" that must be overcome to form products

39

Isothermal definition

~T (~av. KE of molecules)aka NO HEAT EXCHANGE

40

Name the 2 kinds of calorimeters and their distinguishable properties

1) Coffee cup (~P)2) Bomb (~V)

41

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

41

High (+) BDE means the cpd is very ___

stable

42

If Keq > 1, rxn will be...?(if we are starting at standard conditions)

SPONTANEOUS!

43

(+) ∆S=?

increased randomness, more energy available to do work

45

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

46

Think of ∆H as...units?

energy contained w/in chemical bondsunit= Joules

46

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!

47

  • How will the following affect rxn rate?
    • increasing energy of transition state

  • decrease rate
    • because it INCREASES Ea

48

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

48

∆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

50

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

51

If 2 objects are in thermal equilibrium, by definition they have what?

The SAME TEMP!

53

  • How will the following affect rxn rate?
    • increase [ reactants ]

increase rate

55

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

56

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")

57

Define convectionWhat are 2 examples?

hotter sections of fluid rise, cooler portions sinkEX:Air currents & Convection currents (El Nino)

58

The ln of and positive (+) numer LESS than 1 is?

negative (-)

59

For a reaction to occur, what has to happen with regards to collisions?

  1. Reacs must collide with enough energy to overcome the Ea "hill"
  2. Reacs must be in correct spatial orientation

60

What does Keq=1 mean?

rxn is at equilibrium∆G˚=0

61

How to write rate law for a catalyzed rxn

write rate law in same way as normal, w/ [catalyst] added in as a reactant

61

Define the first law of thermodynamics

Energy can't be created nor destroyed

62

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

64

Which type of calorimeter allows for pv work? Why?

Coffee cup, because it's at ~P

65

What do you do to find the "overall order" of a rxn?

Add together the exponents in the rate law

66

"Standard State" definition

a set of conditions set as a REFERENCE POINT for measuring ∆H, ∆G, and ∆S

67

More unstable cpds: -∆Hcombustion?

have a HIGHER ∆Hcombustion, release MORE energy when reacted with O2

68

Slow step=?

rate-determining step

69

Third law of thermodynamics definition

pure crystalline substances at absolute zero have a ∆S of 0

71

What are the 3 types of heat exchange?

1) Convection2) Radiation3) Conduction

73

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 (-)

74

Rate Order graphs: Second order

1/[A] vs time is linear, slope = k

75

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

76

in a 2-step rxn, does the yield of the first rxn affect the Keq of the second?

NOPERS

77

Specific heat capacity definition

describes energy absorption for ONE individual substance

78

What do exponents in a rate law represent?

the "order" of each reactant

79

If Keq < 1, rxn will be?

NON-spontaneous∆G˚ is (-)

80

When calculating ∆Hrxn, what do you need to remember with regards to signs?

bonds FORMED= energy released (-)bonds BROKEN= energy req'd (+)

81

Entropy increases with increasing...

number of moleculestemperaturevolumemoles of gas

83

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)

84

∆E=?

q+W

85

What is a calorimeter?What do we assume about "q?"

a device used to calculate ∆Hassume q = ∆H, which is true at ~P

86

Bond formed as result of rxn=energy ___

released

87

Physics definition for "work"

energy transfer via a force

88

Relationship b/t enzymes & catalysts

Enzyme=biological catalystALL enzymes are catalysts, but not all catalysts are enzymes

89

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

90

When a solute is mixed in solution, ∆S is always ___. Why?

is always (+)something becomes more disordered dissolved in a solution

92

∆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)

94

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)

95

Anything to the zeroth power is equal to?

1

96

∆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)

97

Which thermodynamic elements are "NON-SPONTANEOUS" or "UNFAVORABLE?"

∆G is (+)∆S is (-)∆H is (+)

99

(-) ∆S=?

less randomness, less energy available to do work

100

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)

101

  • How will the following affect rxn rate?
    • increasing [catalyst]

INCREASE rate

102

the word "decomposition" tells us what?

we are going from ONE species to 2+ species (∆S is positive)

103

Thermodynamic Formula

∆G=∆H-T∆S

104

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

105

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 (-)

107

Think of Gibbs Free Energy, ∆G, as...

the amount of "free" or "useful" energy available to do work (**Note**doesnt include pv work)

108

How will the following affect rxn rate? increase temp

increases rate

109

Give an example of ~P heat capacity

water in a beaker (open to the atmosphere)

110

1˚ C= ___ Kelvin

274 K

111

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

112

When values are given for standard state conditions, what thingy is added?

superscript is added --> ∆H˚ "not"

113

Collisions cause?

reactions!

114

Light colors radiate and absorb ___dark colors radiate and absorb ___

Light: absorb lessDark: absorb more

115

Rate Order graphs: Zeroth order

[A] vs time is linear with slope= -k

116

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

117

Isobaric definition

~P

118

∆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)

120

  • How will the following affect rxn rate?
    • increase Ea

DECREASE rate

121

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

122

Rate Order graphs: first order

ln [A] vs time is linear with slope= -k