CHM1045 Exam 3

What is a solution?

A homogeneous mixture of a solute dissolved in a solvent.

What is a solute?

The substance that is dissolved.

What is a solvent?

The substance that dissolves the solute, usually in greater quantity.

Define molarity (M).

Moles of solute per liter of solution (mol/L).

What does dilution mean?

Adding solvent to decrease the concentration of a solution.

What is a precipitate?

An insoluble solid that forms in a solution during a chemical reaction.

An insoluble solid that forms in a solution during a chemical reaction.

A reaction in which two aqueous solutions form an insoluble product.

What is hydration?

The process in which water molecules surround and separate ions in solution.

What is solubility?

The maximum amount of solute that dissolves in a given amount of solvent at a specific temperature.

Are all nitrates (NO₃⁻) soluble?

Yes, all nitrates are soluble.

Are all acetates (CH₃COO⁻) soluble?

Yes, except for silver acetate (AgCH₃COO), which is slightly soluble.

Are all group 1 (alkali metal) salts soluble?

Yes, all Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺ salts are soluble.

Are all ammonium (NH₄⁺) salts soluble?

Yes, all ammonium salts are soluble.

Are chlorides (Cl⁻), bromides (Br⁻), and iodides (I⁻) soluble?

Yes, except with Ag⁺, Pb²⁺, and Hg₂²⁺.

Are sulfates (SO₄²⁻) soluble?

Yes, except BaSO₄, SrSO₄, PbSO₄, CaSO₄ (slightly).

Are carbonates (CO₃²⁻), phosphates (PO₄³⁻), and chromates (CrO₄²⁻) soluble?

No, except those with group 1 ions and NH₄⁺.

Are hydroxides (OH⁻) soluble?

Mostly insoluble, except group 1 ions and Ca²⁺, Sr²⁺, Ba²⁺ (slightly soluble).

Are sulfides (S²⁻) soluble?

Insoluble except for group 1, group 2, and NH₄⁺ salts.

What is electronegativity?

The ability of an atom to attract electrons in a bond.

What happens when electronegativity difference (ΔEN) = 0?

A nonpolar covalent bond forms (equal sharing of electrons).

What happens when ΔEN is between 0.4 and 1.7?

A polar covalent bond forms (unequal sharing of electrons).

What happens when ΔEN > 1.7?

An ionic bond forms (electron transfer).

What makes a molecule polar?

It contains polar bonds arranged asymmetrically, creating a net dipole.

What makes a molecule nonpolar?

Either all bonds are nonpolar, or polar bonds cancel due to symmetry.

Example of a polar molecule?

H₂O (bent shape, dipole doesn’t cancel).

Example of a nonpolar molecule?

CO₂ (linear shape, dipoles cancel).

What is a Lewis structure?

A diagram showing valence electrons as dots around atoms, illustrating bonding.

What is the octet rule?

Atoms tend to form bonds until they have 8 valence electrons. (Exceptions: H,Be, B, or expanded octets in elements in third period>=)

What is a single bond?

Two shared electrons (one pair).

What is a double bond?

Four shared electrons (two pairs).

What is a triple bond?

Six shared electrons (three pairs).

What is a formal charge?

Valence electrons – (nonbonding electrons + ½ bonding electrons).

What is resonance?

When more than one valid Lewis structure can represent a molecule.

What does VSEPR stand for?

Valence Shell Electron Pair Repulsion theory.

What does VSEPR theory predict?

The shape of molecules based on repulsion between electron pairs.

What is the molecular geometry for 2 electron domains, and what are its characteristics?

Geometry: Linear

Bonding/Lone Pairs: 2 bonding, 0 lone pairs

Bond Angle: 180°

Hybridization: sp

Example: CO₂ or BeCl₂

What is the molecular geometry for 3 electron domains, and what are its characteristics?

Geometry: Trigonal planar

Bonding/Lone Pairs: 3 bonding, 0 lone pairs

Bond Angle: 120°

Hybridization: sp²

Example: BF₃

What is the molecular geometry for 4 electron domains, and what are its characteristics?

Geometry: Tetrahedral

Bonding/Lone Pairs: 4 bonding, 0 lone pairs

Bond Angle: 109.5°

Hybridization: sp³

Example: CH₄

What is the molecular geometry for 5 electron domains, and what are its characteristics?

Geometry: Trigonal bipyramidal

Bonding/Lone Pairs: 5 bonding, 0 lone pairs

Bond Angles: 90°, 120°, 180°

Hybridization: sp³d

Example: PCl₅

What is the molecular geometry for 6 electron domains, and what are its characteristics?

Geometry: Octahedral

Bonding/Lone Pairs: 6 bonding, 0 lone pairs

Bond Angles: 90°, 180°

Hybridization: sp³d²

Example: SF₆

What is the molecular geometry for 3 electron domains (2 bonding, 1 lone pair), and what are its characteristics?

Geometry: Bent (Angular)

Bond Angle: <120°

Hybridization: sp²

Example: SO₂

What is the molecular geometry for 4 electron domains (3 bonding, 1 lone pair), and what are its characteristics?

Geometry: Trigonal pyramidal

Bond Angle: ~107°

Hybridization: sp³

Example: NH₃

What is the molecular geometry for 4 electron domains (2 bonding, 2 lone pairs), and what are its characteristics?

Geometry: Bent (Angular)

Bond Angle: ~104.5°

Hybridization: sp³

Example: H₂O

What is the molecular geometry for 5 electron domains (4 bonding, 1 lone pair), and what are its characteristics?

Geometry: Seesaw

Bond Angles: <120° (equatorial), <90° (axial)

Hybridization: sp³d

Example: SF₄

What is the molecular geometry for 5 electron domains (3 bonding, 2 lone pairs), and what are its characteristics?

Geometry: T-shaped

Bond Angle: <90°

Hybridization: sp³d

Example: ClF₃

What is the molecular geometry for 5 electron domains (2 bonding, 3 lone pairs), and what are its characteristics?

Geometry: Linear

Bond Angle: 180°

Hybridization: sp³d

Example: XeF₂

What is the molecular geometry for 6 electron domains (5 bonding, 1 lone pair), and what are its characteristics?

Geometry: Square pyramidal

Bond Angle: <90°

Hybridization: sp³d²

Example: BrF₅

What is the molecular geometry for 6 electron domains (4 bonding, 2 lone pairs), and what are its characteristics?

Geometry: Square planar

Bond Angle: 90°

Hybridization: sp³d²

Example: XeF₄ or PtCl₄²⁻

What is hybridization?

The mixing of atomic orbitals to form new hybrid orbitals that can form bonds.

What is an sp hybrid orbital?

Formed from one s and one p orbital; linear geometry.

What is sp² hybridization?

One s and two p orbitals combine; trigonal planar geometry.

What is sp³ hybridization?

One s and three p orbitals combine; tetrahedral geometry.

What is a sigma (σ) bond?

A bond formed by head-on overlap of orbitals.

What is a pi (π) bond?

A bond formed by sideways overlap of p orbitals.

What are intermolecular forces (IMFs)?

Attractive forces between neighboring molecules.

What are the three main types of IMFs?

London dispersion forces, dipole–dipole interactions, and hydrogen bonding.

What is a hydrogen bond?

A strong dipole–dipole attraction between H and N, O, or F atoms.

What is an ion–dipole interaction?

Attraction between an ion and a polar molecule.

How do IMFs affect boiling point?

Stronger IMFs lead to higher boiling points.

What are London dispersion forces?

Weak temporary attractions due to momentary dipoles in all molecules.

What are dipole–dipole interactions?

Attractions between oppositely charged ends of polar molecules.

What is an exothermic reaction?

A reaction that releases heat (ΔH < 0). Feeling hotter because surroundings gain heat.

What is an endothermic reaction?

A reaction that absorbs heat (ΔH > 0). Feeling colder because the temperature of the surroundings lowers.

What is enthalpy (ΔH)?

The heat content of a system at constant pressure.

What is internal energy (E)?

The sum of kinetic and potential energy in a system

What are the three types of systems in thermodynamics?

Open (matter & energy exchange), Closed (energy only), Isolated (no exchange).

What is work (w) in thermodynamics?

Energy transferred when a force moves an object a distance.

What determines if ΔE is positive or negative?

ΔE > 0 when energy enters the system; ΔE < 0 when energy leaves.

What is calorimetry?

The measurement of heat changes during physical or chemical processes.

What does a calorimeter measure?

The heat change of a reaction or process, usually at constant pressure in a coffee-cup calorimeter.

What is enthalpy (ΔH)?

The heat released or absorbed at constant pressure; equal to H(products) – H(reactants).

What does “standard conditions” or mean in thermochemistry?

1 atm pressure and 25°C (298 K).

Formula for heat transfer involving temperature change?

q=mcΔT (mass × specific heat × change in temperature)

What does Hess’s Law state?

The total enthalpy change of a reaction is the sum of the enthalpy changes of individual steps.

In calorimetry, if the solution temperature increases, what can we say about the reaction?

The reaction is exothermic.

What is diffusion?

The spreading of gas particles through space or another substance.

What is effusion?

The escape of gas molecules through a tiny hole into a vacuum.

What does the Combined Gas Law relate?

Pressure, volume, and temperature: (P1(V1))/(T1) = (P2(V2))/(T2)

What is Standard Temperature and Pressure (STP)?

Temperature = 273 K; Pressure = 1 atm.

What is the molar volume of an ideal gas at STP?

22.4 L/mol

What does Kinetic Molecular Theory (KMT) explain?

How molecular motion gives rise to gas properties such as pressure and temperature.

According to KMT, what determines a gas particle's kinetic energy?

Temperature; average kinetic energy is proportional to the absolute temperature.

What is the formula for average kinetic energy of a gas molecule?

3/2 kT (Boltzmann constant × temperature)

What happens to gas volume when temperature increases (at constant pressure)?

Volume increases (Charles’ Law).

What is the ideal gas law?

PV=nRT

What is a phase diagram?

A graph showing state of matter (solid, liquid, gas) under different temperature and pressure conditions

What is the triple point?

The unique temperature and pressure where all three phases exist in equilibrium.

What is the critical point?

The temperature and pressure above which a substance cannot exist as a liquid.

What is vapor pressure?

The pressure exerted by a vapor in equilibrium with its liquid at a given temperature.

How does temperature affect vapor pressure?

Increasing temperature increases vapor pressure.

What does a phase diagram of water show that is unusual?

The solid–liquid boundary slopes backwards, meaning ice melts under pressure.

What happens at the boiling point?

Vapor pressure equals external pressure.

What is sublimation?

The transition of a solid directly to a gas.

What is deposition?

The transition from gas directly to solid.

What does increasing external pressure generally favor?

The phase with the smaller volume (usually solids or liquids).