MCAT Chemistry > Reference Guide

Background

MCAT Chemistry Constants

Planck's Constant (h) = 6.626 x 10-34 Js

Rydberg constant (RH) = 2.2 x 10-18 J/electron

Speed of Light in a Vacuum (c) = 3.0 x 108 m/s

Avogadro's Number (1 mole) = 6.022 x 1023 particles

1 atm = 760 mm Hg = 760 torr = 101.325 kPa

Boltzmann constant (k) = 5.67 x 10-8 J/Sm2K4

Gas Constant (R) = 8.21 x 10-2 (Latm)/(molK) or 8.314 J/Kmol

1 cal = 4.184 J

1 AMU = 1/12 of a C12 atom = 1.66 x 10-19 g

STP (Standard Temperature and Pressure) = 1 atm & 273K (0°C) (gas law equations)

Standard Conditions = 1 atm & 298K (enthalpy, entropy, free energy changes, & voltage)

Volume of 1 mole of gas at STP = 22.4L

MCAT Chemistry Equations

Atomic Structure

See Atomic Structure

E = hf

Angular Momentum= L = (nh)/2π

Energy of the electron=E = -RH/n2

E = (hc)/λ

E = -RH[(1/nf2) – (1/(ni2)]

Periodic Table of Elements

See Periodic Table of Elements

Zeff increases from left to right across a period

Zeff increases from top to bottom down a group

Atomic Radius decreases from left to right across a period

Atomic Radius increases from top to bottom down a group

Ionization energy increases from left to right across a period

Ionization energy decreases from top to bottom in a group

Electronegativity increases across a period from left to right

Electronegativity decreases in a group from top to bottom

Chemical Reactions

See Chemical Reactions

Formal Charge = Vvalence – Nnon-bonding – 1/2 Nbonding

Stoichiometry

See Stoichiometry

Gram Equivalent Weight = (molar mass)/n

Equivalents =(mass of compound (g))/GEW

Molarity = Normality/n

Percent Composition = (mass of x)/(formula weight of compound) x 100

% yield = (actual yield)/(theoretical yield) x 100

Kinetics and Equilibrium

See Kinetics and Equilibrium

rate = -1Δ[A]/aΔT = -1Δ[B]/bΔT = -1Δ[C]/cΔT = -1Δ[D]/dΔT

Rate = k[A]x[B]y[C]z

Rate = Fz

Kc = Keq = ([C]c [D]d)/([A]a [B]b) = kf/kr = Qc

Thermochemistry

See Thermochemistry

ΔU = Q – W

Q = mcΔT

ΔHrxn = Hproducts - Hreactants

ΔH°rxn = Σ(ΔH°products) - Σ(ΔH°reactants)

ΔHrxn = ΣΔHbonds-broken + ΣΔHbonds-formed

ΔS = Q/T

ΔS°rxn = ΣΔS°products - ΣΔS°reactants

ΔG = ΔH – TΔS

ΔG°rxn = Σ(ΔG°fproducts) – Σ(ΔG°freactants)

ΔG°rxn = -RTln(Keq)

ΔGrxn = RTln(Q/Keq)

Phases of Matter

See Phases of Matter

ΔP = P°A – PA

ΔP = XBA

PA = XBB

M = (mol solute)/(kg solvent)

ΔTb = ikBM

ΔTf = = ikfm

Π = iMRT

KE = ½mv2 = 3/2kT

μrms = √3RT/Mm

(r1/r2) = √((Mm)2/(Mm)1)

n/V = k

n1/V2 = n1/V2

PV = nRT

ρ = M/V = P(Mm)/RT

V2 = V1 (P1/P2)/(T2/T1)

P1V1 = P2V2

V/T = k

V1/T1 = V2/T2

V/T = nR/P = constant

PT = PA + PB + PC

PA = PTXA

XA = (na/nt)

(P +(n2a) / V2)(V – nb) = RT

Solutions

See Solutions

Mole Fraction (X) = (# of compound mol)/(total # species mol) = 1

Molality (m) = (Moles solute)/(kg solvent)

Normality (N) = (Number of equivalents solute)/(liter of solution)

Dilution = M1V1 = M2 V2

ksp = [An+]m[Bn-]n

I.P. = [An+]m[Bn-]n

Acids and Bases

See Acids and Bases

pH = -log⁡[H+] = log⁡(1/[H+])

pOH = -log⁡[OH-] = log⁡(1/[OH-])

Ka = [H30+]([A-]/[HA])

Electrochemistry

See Electrochemistry

εmf° = E°cathode - E°anode = E°red + E°ox

ΔG = ΔG° = -nFεcell°

εcell = εcell° - (RT/nF)lnQ

ΔG° = -RTln(keq) = -nFE°cell = RTln(keq)

MCAT Chemistry

Chemistry Topics