GOB Chemistry Exam 2 Study Guide: Gases, Chemical Reactions, Molecular Geometry, and Bonding

Gases and Gas Laws

Properties of Gases

Gases are one of the fundamental states of matter, characterized by their ability to expand and fill any container, low density, and high compressibility. Understanding the behavior of gases is essential in chemistry, especially in biological and health-related contexts.

• Ideal Gas Law: Relates pressure, volume, temperature, and amount of gas.

• Partial Pressure: The pressure exerted by a single gas in a mixture.

• Unit Conversions: Pressure can be measured in atm, mm Hg, or torr.

Formula:

$PV = nRT$

Where:

• P = pressure (atm)

• V = volume (L)

• n = moles of gas

• R = gas constant ($0.08206\ \frac{L\cdot atm}{mol\cdot K}$ or $8.314\ \frac{J}{mol\cdot K}$)

• T = temperature (K)

Dalton's Law of Partial Pressures

In a mixture of gases, each gas exerts a pressure independently of the others. The total pressure is the sum of the partial pressures.

Formula:

$P_{\text{total}} = P_1 + P_2 + P_3 + \ldots$

• Partial pressure calculation: $P_i = \frac{n_iRT}{V}$

Gas Law Applications

• Boyle's Law: $P_1V_1 = P_2V_2$ (at constant T and n)

• Charles's Law: $\frac{V_1}{T_1} = \frac{V_2}{T_2}$ (at constant P and n)

• Avogadro's Law: $\frac{V_1}{n_1} = \frac{V_2}{n_2}$ (at constant P and T)

Example Table: Pressure Unit Conversions

Unit	Conversion to atm
mm Hg	1 atm = 760 mm Hg
torr	1 atm = 760 torr
Pa	1 atm = 101325 Pa

Example:

• Calculate the partial pressure of N2 in a mixture using the ideal gas law.

• Convert 128 mm Hg to atm: $\frac{128}{760} = 0.168$ atm

Chemical Reactions and Stoichiometry

Types of Chemical Reactions

Chemical reactions can be classified into several types based on the changes occurring in the reactants and products.

• Combination (Synthesis): Two or more substances combine to form one product.

• Decomposition: A single compound breaks down into two or more simpler substances.

• Single Replacement: One element replaces another in a compound.

• Double Replacement: Exchange of ions between two compounds.

Balancing Chemical Equations

Balancing ensures the same number of atoms of each element on both sides of the equation.

• Use coefficients to balance atoms.

• Example: $\text{CH}_4 (g) + 2\text{Cl}_2 (g) \rightarrow \text{CCl}_4 (l) + 4\text{HCl} (g)$

Stoichiometry

Stoichiometry involves calculations based on the relationships between reactants and products in a chemical reaction.

• Mole-to-mole conversions: Use balanced equations to relate moles of reactants and products.

• Limiting Reactant: The reactant that is completely consumed first, limiting the amount of product formed.

• Percent Yield: $\text{Percent Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100\%$

Example Table: Reaction Types

Type	General Form	Example
Combination	A + B → AB	2H2 + O2 → 2H2O
Decomposition	AB → A + B	2KClO3 → 2KCl + 3O2
Single Replacement	A + BC → AC + B	Zn + 2HCl → ZnCl2 + H2
Double Replacement	AB + CD → AD + CB	AgNO3 + NaCl → AgCl + NaNO3

Example:

• Given 10.0 g NaN3 and 30.0 g O2, determine the limiting reactant and calculate the mass of O2 remaining after the reaction.

Molecular Geometry and Bonding

Electron Domains and Molecular Geometry

The arrangement of electron domains around a central atom determines the molecular geometry.

• Electron Domain: Regions where electrons are likely to be found (bonds or lone pairs).

• VSEPR Theory: Valence Shell Electron Pair Repulsion theory predicts shapes based on repulsion between electron domains.

Common Geometries

Electron Domains	Geometry	Example
2	Linear	CO2
3	Trigonal planar	BF3
4	Tetrahedral	CH4
5	Trigonal bipyramidal	PCl5
6	Octahedral	SF6

Hybridization

Atomic orbitals mix to form new hybrid orbitals suitable for bonding.

• sp: Linear geometry

• sp2: Trigonal planar geometry

• sp3: Tetrahedral geometry

Example:

• XeF4 has 6 electron domains and square planar geometry.

• In SO3, the central atom has 3 bonds and 3 π bonds.

Molar Mass and Mole Calculations

Molar Mass

Molar mass is the mass of one mole of a substance, expressed in g/mol.

• Calculated by summing the atomic masses of all atoms in a formula.

• Example: Molar mass of C31H46O2 (phytonadione) = 450.7 g/mol

Mole and Avogadro's Number

One mole contains $6.02 \times 10^{23}$ entities (atoms, molecules, ions).

• Used to convert between mass, moles, and number of particles.

Example Table: Mole Calculations

Quantity	Conversion Factor
Mass to Moles	$\frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$
Moles to Particles	$\text{moles} \times 6.02 \times 10^{23}$

Example:

• Calculate the number of nitrogen atoms in 8.0 × 10-3 g of acrivastine (C22H29N2O2).

Polarity and Intermolecular Forces

Polarity

Molecular polarity depends on the difference in electronegativity and the geometry of the molecule.

• Polar Molecule: Has a net dipole moment due to uneven distribution of electrons.

• Nonpolar Molecule: Even distribution of electrons; no net dipole moment.

Intermolecular Forces

• London Dispersion: Present in all molecules, especially nonpolar.

• Dipole-Dipole: Present in polar molecules.

• Hydrogen Bonding: Strong dipole-dipole interaction involving H bonded to N, O, or F.

Example:

• CO is polar; CH4 is nonpolar.

Additional info:

• Some questions involve Lewis structures and bond angles, which are important for understanding molecular shape and reactivity.

• Pressure, volume, and temperature relationships are central to gas law calculations in biological and environmental chemistry.

• Stoichiometry and limiting reactant concepts are essential for predicting product amounts in chemical reactions.