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MCAT chem > Equations > Flashcards

Equations Flashcards

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1
Q

Equation needed for the heat of a phase change.

A

q = n x ∆H of that specific phase change (e.g, heat of fusion or heat of evaporation)

Note: during a phase change temperature does not change since energy goes into changing the phase.

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2
Q

Equation needed for heat involved in a temperature change (e.g. a liquid heating up but not evaporating)

A

q = mc∆T

c = specific heat 
C = heat capacity = cm

therefore q = C∆T too

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3
Q

ideal gas law

A

PV = nRT

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4
Q

equation used when comparing two scenarios of one gas

A

P1V1 / T1 = P2V2 / T2

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5
Q

Van der Waals equation for non ideal gases

A

two corrections involving a and b

a: correction for intermolecular forces experienced at high pressures and low volumes. a is larger for molecules with stronger IMF’s such as hydrogen bonding
b: correction for gases taking up space. b is bigger for bigger gases

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6
Q

grahams law of effusion

A

effusion rate A molar mass A
——————– = square root of ————–
effusion rate B molar mass B

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7
Q

Thermodynamic equation relating ∆G° and K (at equilibrium). And the equation relating ΔG and Q (not at equilibrium)

A

At eq: ∆G° = -RTlnK

Not at eq: ΔG = ∆G° + RTlnQ

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8
Q

pH calculation and [H+] calculation

A

[H+] = 10^ −pH

pH = -log[H+]

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9
Q

Calculation for Gibbs free energy (thermodynamics)

A

ΔG = ΔH - TΔS

another equation to know is

ΔH = ΔE - PΔV

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10
Q

The Henderson-Hassalbalch equation

A

pH = pka + log (base form / acid form)

note if we are using a buffer with a base and its conjugate acid (instead of acid / conj. base)

pOH = pKb + log (acid form / base form)

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11
Q

formula used to determine how much base to add to an acidic solution (or vice versa) to completely neutralize it.

A

[A] x VA = [B] x VB

V is volume

this is the equation used in titrations to determine the unknown solutions concentration

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12
Q

equation to find the ∆G° from a galvanic cell

A

∆G° = -nFE°

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13
Q

the equation to find E of a cell when not at standard conditions = the Nernst equation. What does it correct for?

A

derived from ΔG = ΔG° + RTlnQ (replacing G’s with -nFE and rearranging)

E = E° - (RT/nF) lnQ

note that the Nernst equation is with a (-) sign
Nernst = negative

the delta G equation has a (+) sign

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14
Q

finding coulombs from current

A

Q = It

Q = coulombs of charge (electrical energy)
I = current (C/s)
t= seconds
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15
Q

what is Avogadro’s number?

A

The number of particles / entities of any substance in one mole of that substance

6 x 10^23

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16
Q

in terms of the atom, what does A, Z, and N represent?

A 
Z = atomic number = number of protons 
A = atomic mass = number of P + N
N = number of neutrons

A = N + Z

17
Q

What are the effects of A, N, and Z in all 5 types of radioactive decay?

A

Z N A
Alpha: -2 -2 -4 (emission of helium)

Beta (-) +1 -1 0 n –> p + electron

Beta (+) -1 +1 0 p —> n + positron

electron -1 +1 0 p + electron —> n
capture
gamma 0 0 0 X(excited) —> x (chill)

18
Q

what is the equation for formal charge?

A

FC = Valence e - lone pair e - number of bonds

19
Q

what is the equation of Zeff?

A

Zeff = Z - S

Z = atomic number 
S = shielding electrons (take all e and subtract valence e)
20
Q

true or false, intermolecular force trend goes

ion - ion > ion - Dipole > H-bond > D-D > induced dipole > instantaneous dipole (London dispersion)

A

True!! all ionic interactions beat H bonds. H bonds are the strongest in most organic situations

21
Q

true or false, periodic trends

EA, EN, IE all increase up and to the right

acidity increases down and to the right

radius increases down and to the left

A

true

22
Q

F-O-N-Cl-Br-(I=S)-C=H

A

note that iodine and Sulphur have similar electronegative

23
Q

how do you calculate the delta H (standard) of a reaction?

A

Heat of formation products - Heat of formation reactants

24
Q

First law of thermodynamics

A

the energy in the universe is constant

∆E (system) = Q - W

This equation puts everything in terms of the system

Q > 0 : heat is absorbed BY the system
Q < 0 : heat is release BY the system

W > 0 : work is done BY the system

W < 0 : work is done ON the system

25
Q

true or false, spontaneous reactions have a positive ∆S

A

true, this is law 2 of thermodynamics

26
Q

what is true of the following processes

isothermal
isochoric
isobaric
adiabatic

A

isothermal –> temperature does not change therefore P varies with 1/V (inversely proportional)

Isobaric –> pressure does not change (V varies with T)

Isochoric –> volume does not change ( P varies with T)

Adiabatic –> there is no heat exchange

27
Q

Avodardo’s law says the V varies with moles. At STP what is true?

A

one mole of gas takes up 22.4 litres of space

therefore for n moles

Vgas at STP = n (22.4)

28
Q

true or false, for an isothermal, isochoric, or isobaric process, we can hold one variable constant and manipulate PV=nRT. This lets us examine before and after situations. E.g.

isothermal: P1V1 /nRT1 = P2V2 / nRT2

temp is constant and moles should be consant therefore

P1V1 = P2V2
what is the equation for an isochoric process?

A

P1 / T1 = P2/ T2

29
Q

in all iso processes, one variable is fixed. What is the combined gas equation when none are fixed and ONLY moles stays constant?

A

P1V1 / T2 = P2V2 / T2

30
Q

What is Van Der Waals equation?

A

Corrects for problems in PV = nRT

first term corrects for IMF’s

second term corrects for mass / volume taken up by the gas

31
Q

To find the reaction rate of the equation

2A + B –> C

what two equation involving changing concentration can we use?

A 
- 1/2 x ∆ [A} 
 or 
-∆[B] 
or 
\+ ∆[C]

note that we take the inverse of the coefficient if there is one!!!

32
Q

formula for pH

A

pH = - long [H+]

pOH = - log [OH]

33
Q

true or false, at 25 degrees

Kw = [H+][OH-] = 1.0 x 10^-14

A

true, only temperature can alter Kw

additionally at 25 degrees

pH + pOH = 14

and KaKb = Kw

34
Q

what is the calculation for pKa?

A

pKa = -log Ka

where Ka = [A-][H+] / [HA]

35
Q

degree of unsaturation of chemical compound

A

2n + 2 - x
d = —————
2

where n is the number of carbons and x is number of hydrogens and any monovalent atom (halogens)

oxygen is ignored
for every nitrogen we add one carbon and on hydrgen

36
Q

what is the degree of unsaturation of..

C4H6O

C3H5Br

C5H7N

A

C4H6O = 2(4) + 2 - 6 / 2
8 + 2 - 6 = 4/2 = 2

C3H5Br = 1

C5H7N

2(5) + 2 - 7 / 2 if no nitrogen was there but instead

2(6) + 2 - 8 / 2 = 3

MCAT chem (11 decks)

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