AP Chemistry 1-212

Strong acids

HCl, HBr, HI, HClO₄, HNO₃, H₂SO₄

H₂ bond energy & bond type

Single covalent bond, ~400+ kJ/mol

F₂, Cl₂, Br₂, I₂ bond energies & bond types

Single covalent bonds; bond energies range from ~150-250 kJ/mol

O₂ bond energy & bond type

Double covalent bond, ~500 kJ/mol

N₂ bond energy & bond type

Triple covalent bond, ~900 kJ/mol

Strong bases in AP Chemistry

All soluble metal hydroxides (e.g., NaOH, KOH, Ba(OH)₂)

Celsius to Kelvin conversion

K = 273 + °C

Percent error formula

%Error = [(Experimental - Correct) ÷ Correct] × 100

Importance of sign in percent error

It shows whether the measurement is above or below the actual value.

How many significant digits should you use on the AP Exam?

Three significant digits (3), for 95% of all questions. If it is a simple calculation, be careful and follow the sig fig rules.

Situations requiring attention to significant figures

When performing lab measurements using addition/subtraction or simple single operations like molar mass calculations

Most accurate volume-measuring devices (3 of them)

Volumetric flask (fixed volume), burette (variable volume), pipette (variable volume)

Relatively accurate lab devices (2 of them)

Graduated cylinder, electronic balance

Devices not considered accurate for volume measurements (2 of them)

Beaker, Erlenmeyer flask

Molar mass of H₂

2.0 g/mol

Molar mass of N₂

28 g/mol

Molar mass of O₂

32 g/mol

Molar mass of H₂O

18 g/mol

Molar mass of CO₂

44 g/mol

Molar mass of NaOH

40.0 g/mol

Atomic number of an element: location and meaning

The number above the element symbol on the AP periodic table; number of protons

Mass number

Mass number = number of protons + number of neutrons of an atom of a specific isotope of an element

• always whole number

• not shown on AP periodic table

Relationship of mass number to atomic mass

Mass number is the closest whole number to the element's atomic mass

(average) atomic mass

The weighted average of all the naturally occurring isotopes of an element; in amu or g/mol; listed on periodic table for each element.

Implication of average atomic mass close to a whole number

It means the element likely has one dominant isotope

Mass spectrometer

A tool that sorts isotopes of elements by mass and shows their relative abundance

Using mass spectrometry data in AP Chemistry

Use the relative abundances and mass numbers to calculate average atomic mass; compare with periodic table value

Key differences between isotopes of the same element

They differ in the number of neutrons and their atomic mass

Coulombic forces definition

The attractions between opposite charges and repulsions of similar charges

How does sign and magnitude of charge affect Coulombic forces?

Like charges → repel; Unlike charges → attract; Greater magnitudes → stronger attraction/repulsion.

How does distance affect Coulombic forces?

Greater distance → weaker forces; Smaller distance → stronger forces.

Avogadro's number

6.02 × 10²³ particles/mol.

Limiting reactant

The reactant that determines the extent of the reaction and product amounts, found by setting up an ICE Chart and dividing mole amounts by stoichiometric coefficients.

Empirical Formula: definition

The simplest whole-number ratio of atoms in a compound.

Finding empirical formula steps

1. Find the number of mol of each element.

2. Divide all mol values by the smallest mol amount.

3. If necessary, multiply the resulting ratio to eliminate fractions.

How does the molar mass compare to the empirical molar mass?

The molar mass of a compound will be a whole number multiple of the empirical molar mass.

Mole fraction formula

mol amount of X / total mols

Soluble cations / anions

NO₃⁻ , Na⁺, K⁺, and NH₄⁺ form only soluble compounds and are spectator ions (not included in net ionic equations).

What unit does millimol solute / volume in mL give you?

Gives you molar concentration in mol/L (M).

Molecular equation for NaCl and AgNO₃ reaction

NaCl(aq) + AgNO₃(aq) → NaNO₃(aq) + AgCl(s).

Complete ionic equation for NaCl and AgNO₃ reaction

Na⁺ + Cl⁻ + Ag⁺ + NO₃⁻ → Na⁺ + NO₃⁻ + AgCl(s).

Net ionic equation for NaCl and AgNO₃ reaction

Ag⁺ + Cl⁻ → AgCl(s).

Weak acids and bases in net ionic equations

They are shown as molecules, not ions (undissociated, while the strong acids/bases fully dissociate).

Net ionic equation for strong acid-strong base reaction

H⁺ + OH⁻ → H₂O(l).

Convert torr or mmHg to atm

torr ÷ 760 = atm.

Metric unit for pressure

The pascal (Pa); the kPa is also used, but doesn’t need to be memorized.

Ideal gas law equation

PV = nRT.

Calculating pressure when gas collected over water: what should we do?

Subtract water vapor pressure from the total pressure.

Standard conditions for STP (Standard Temperature & Pressure)

1 atm, 0°C.

Molar gas volume at STP (could also be found using PV = nRT; this is just a handy memorization)

22.4 L/mol

Formula to calculate molar mass of a gas using density

Molar mass = (Density × R × T) / P (molar mass of a gas is DiRTy over P)

Density of a gas @STP

Density@STP = molar mass / 22.4 L/mol

Molecular speed of gases

Lighter molecules move faster.

Average speed on Maxwell-Boltzmann curve

Just to the right of the peak.

Effect of molecular speed on Maxwell-Boltzmann curve

Faster average speed makes the curve wider and more spread out.

Ideal Gas Law Assumptions (5)

1. negligible volume

2. high temp

3. elastic collisions (no energy lost)

4. constant, random motion

5. no IMFs

Non-ideal gas conditions

High pressure and low temp.

Non-ideal gas behavior at high pressure

Molecules are closer together, so intermolecular attractions interfere with motion.

Non-ideal gas behavior at low temperatures

Molecules move more slowly, allowing IMFs to dominate.

Source of higher-than-expected pressure in non-ideal gas

Large molecular volume reduces free space for movement.

Lower-than-expected pressure in non-ideal gas

Strong intermolecular attractions cause molecules to stick together.

Partial pressure of a gas in a mixture

Partial Pressure = Total Pressure * Mol Fraction

Specific heat capacity of water

4.18 J/g°C (pretty high)

Substances with low specific heat capacities

Metals (typically less than one)

Formula for heat in a calorimeter

q = mass × ΔT × specific heat capacity

Limiting factor in accuracy of q = mCΔT for sig figs

Usually ΔT because it is the difference between two close temperature values.

Formula for calculating ΔH from calorimetry

Calorimeter ΔT is positive; what is ΔH and endo/exo?

The reaction is exothermic; ΔH is negative.

Calorimeter ΔT is negative; what is ΔH and endo/exo?

The reaction is endothermic; ΔH is positive.

ΔH definition

The change in potential energy (enthalpy) of a reaction.

Negative ΔH implications

Exothermic; potential energy decreases; bond energy increases.

Positive ΔH implications (endo/exo, potential energy, bond energy, thermodynamic favorability)

• Endothermic

• potential energy increases

• bond energy decreases

• reaction is thermodynamically unfavorable unless driven by an increase in entropy (S) or external energy (e.g., electrolytic cell).

Units of ΔH

kJ/mol_rxn or kJ per mole of product.

Bonds in an endothermic reaction

Stronger bonds in reactants are broken, weaker bonds in products are formed.

Potential energy in an endothermic reaction

KE is absorbed from surroundings; PE increases.

Exothermic Reaction

A reaction where weaker bonds in the reactants are broken, and stronger bonds in the products are formed (bond energy increases).

Kinetic Energy in Exothermic Reaction

KE is released to surroundings; the surroundings to get hotter.

Potential Energy in Exothermic Reaction

Potential energy decreases (ΔH = -).

Thermodynamic Favorability of Exothermic Reaction

Exothermic reactions are thermodynamically favorable.

Heat (KE) in Exothermic Reaction

Heat is a product; ΔH is negative.

Example of Thermodynamically Favorable Reaction

A → B + kinetic energy (heat); exothermic

Heat (KE) in Endothermic Reaction

Heat is a reactant; ΔH is positive.

Example of Thermodynamically Unfavorable Reaction (endothermic)

A + kinetic energy → B

What is ΔH(f), Enthalpy of Formation?

The reaction enthalpy to make 1 mole of a substance from its elements in their most common form at 25°C; most are exothermic (ΔH(f) is negative).

ΔHf of Elements

0 kJ/mol by definition.

Exception to Standard ΔH(f) of Elements

If the element is not in its most common form at 25°C, its ΔH(f) is not zero.

Calculating ΔHrxn Using ΔHf Values

ΔHrxn = ΣΔHf (products) - ΣΔHf (reactants)

Calculating ΔHrxn Using Bond Energies (BE)

ΔH(rxn) = ΣBE (reactants) - ΣBE (products)

• the only equation where reactants come first.

Relationship Between Wavelength, Frequency, and Photon Energy

Shorter wavelengths have higher frequencies and greater photon energies.

Unit for Frequency

Hertz (Hz), or 1/second (1/s or s⁻¹).

Calculating Energy of a Photon from Wavelength in nm (2-step method)

Because c is in m/s you must change 100 nm to 100 E-9 m

1-step Equation to Calculate Photon Energy from Wavelength in nm

E = h × c / (λ × 10⁻⁹) (Mnemonic: E = hic divided by nine negative lambs)

Converting Photon Energy to Energy per Mole of Photons

E (mol photons) = E (photon) × 6.02 × 10²³

Effect of Absorbed Photons

They transfer energy, causing electrons or molecules to become excited or ionized.

General Effect of Different Photon Energies on Substances

X-rays ionize atoms; ultraviolet and visible light excite electrons; IR and microwaves cause molecular vibrations and rotations.

Visible light: lowest wavelength vs. highest wavelength

400 nm: violet (most energy); 700 nm: red (least energy)

Order of orbital filling up to 5s² (all that’s needed for AP)

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s².

Order of ionization

Grouped by principal energy level: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² — electrons ionize from the highest energy level down.

Difference between filling and ionization order

• Filling order: 4s² filled before 3d¹⁰.

• Ionization order: 4s electrons are removed before 3d electrons. Follows grouping order.

Complete electron configuration

Lists all subshells in the order of energy levels (as you would see on a PES graph (3d comes before 4s)).