MCAT Chemistry > Reference Guide

## Background

## MCAT Chemistry Constants

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

Rydberg constant (R_{H}) = 2.2 x 10^{-18} J/electron

Speed of Light in a Vacuum (c) = 3.0 x 10^{8} m/s

Avogadro's Number (1 mole) = 6.022 x 10^{23} particles

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

Boltzmann constant (k) = 5.67 x 10^{-8} J/Sm^{2}K^{4}

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 C^{12} 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 = -R_{H}/n^{2}

E = (hc)/λ

E = -R_{H}[(1/n_{f}^{2}) – (1/(n_{i}^{2})]

### Periodic Table of Elements

See Periodic Table of Elements

Z_{eff} increases from left to right across a period

Z_{eff} 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

Formal Charge = V_{valence} – N_{non-bonding} – 1/2 N_{bonding}

### 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

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

Rate = k[A]^{x}[B]^{y}[C]^{z}

Rate = Fz

K_{c} = K_{eq} = ([C]^{c} [D]^{d})/([A]^{a} [B]^{b}) = k_{f}/k_{r} = Q_{c}

### Thermochemistry

See Thermochemistry

ΔU = Q – W

Q = mcΔT

ΔH_{rxn} = H_{products} - H_{reactants}

ΔH°_{rxn} = Σ(ΔH°_{products}) - Σ(ΔH°_{reactants})

ΔH_{rxn} = ΣΔH_{bonds-broken} + ΣΔH_{bonds-formed}

ΔS = Q/T

ΔS°_{rxn} = ΣΔS°_{products} - ΣΔS°_{reactants}

ΔG = ΔH – TΔS

ΔG°_{rxn} = Σ(ΔG°f_{products}) – Σ(ΔG°f_{reactants})

ΔG°_{rxn} = -RTln(K_{eq})

ΔG_{rxn} = RTln(Q/K_{eq})

### Phases of Matter

See Phases of Matter

ΔP = P°_{A} – P_{A}

ΔP = X_{B}P°_{A}

P_{A} = X_{B}P°_{B}

M = (mol solute)/(kg solvent)

ΔT_{b} = ik_{B}M

ΔT_{f} = = ik_{f}m

Π = iMRT

KE = ½mv^{2} = 3/2kT

μ_{rms} = √3RT/M_{m}

(r_{1}/r_{2}) = √((M_{m})_{2}/(M_{m})_{1})

n/V = k

n_{1}/V_{2} = n_{1}/V_{2}

PV = nRT

ρ = M/V = P(M_{m})/RT

V_{2} = V_{1} (P_{1}/P_{2})/(T_{2}/T_{1})

P_{1}V_{1} = P_{2}V_{2}

V/T = k

V_{1}/T_{1} = V_{2}/T_{2}

V/T = nR/P = constant

P_{T} = P_{A} + P_{B} + P_{C} …

P_{A} = P_{T}X_{A}

XA = (n_{a}/n_{t})

(P +(n_{2}a) / V_{2})(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 = M_{1}V_{1} = M_{2} V_{2}

k_{sp} = [A^{n+}]^{m}[B^{n-}]^{n}

I.P. = [A^{n+}]^{m}[B^{n-}]^{n}

### Acids and Bases

See Acids and Bases

pH = -log[H^{+}] = log(1/[H^{+}])

pOH = -log[OH^{-}] = log(1/[OH^{-}])

K_{a} = [H_{3}0^{+}]([A^{-}]/[HA])

### Electrochemistry

See Electrochemistry

ε_{mf}° = E°_{cathode} - E°_{anode} = E°_{red} + E°_{ox}

ΔG = ΔG° = -nFε_{cell}°

ε_{cell} = ε_{cell}° - (RT/nF)lnQ

ΔG° = -RTln(k_{eq}) = -nFE°_{cell} = RTln(k_{eq})