General Chemistry Exam Study Guide: Key Concepts, Equations, and Problem-Solving Strategies

General Chemistry Exam Study Guide

Directions and Exam Format

This exam consists of multiple-choice, true/false, fill-in-the-blank, and free-response questions. Calculators are permitted, but cell phones and other electronic devices are not allowed. All work must be shown for full credit, and answers must be recorded on the Scantron form using a dark blue or black ink pen.

Key Equations and Constants

Temperature Conversions

• Celsius to Fahrenheit: $^\circ F = \frac{9}{5}(^\circ C) + 32$

• Fahrenheit to Celsius: $^\circ C = \frac{5}{9}(^\circ F - 32)$

• Celsius to Kelvin: $K = ^\circ C + 273.15$

• Kelvin to Celsius: $^\circ C = K - 273.15$

Volume Formulas

• Sphere: $V_{\text{sphere}} = \frac{4}{3}\pi r^3$

• Cylinder: $V_{\text{cylinder}} = \pi r^2 h$

• Cube: $V_{\text{cube}} = l^3$

• Rectangular Solid: $V_{\text{solid}} = lwh$

Atomic Mass Calculation

• $\text{atomic mass} = \sum (\text{fractional abundance} \times \text{mass})_i$

Conversion Factors

• 1 L = 1.0567 qt

• 1 gal = 4 qt

• 1 kg = 2.2046 lb

• 1 lb = 453.59 g

• 1 in = 2.54 cm

• 1 metric ton = 1000 kg

• 1 km = 0.62137 mi

• 4 cups = 1 qt

Constants

• $\pi = 3.1416$

• Avogadro's number: $N_A = 6.022 \times 10^{23}$ mol-1

Fundamental Concepts

Atoms, Elements, and Compounds

• Atoms are the basic units of matter, composed of protons, neutrons, and electrons.

• Elements are pure substances consisting of only one type of atom.

• Compounds are substances formed from two or more elements chemically combined in fixed ratios.

• In compounds, the total charge is zero; cations and anions combine to balance charges.

Physical and Chemical Properties

• Ductility: The ability of a material to be drawn into a thin wire.

• Heterogeneous Mixture: A mixture that can scatter light, such as a colloid.

• Condensation: Phase change from gas to liquid.

Classification of Matter

• Mixtures: Can be homogeneous (uniform composition) or heterogeneous (non-uniform composition).

• Pure Substances: Elements and compounds.

Significant Figures

• Significant figures reflect the precision of a measurement.

• Example: The number 3400 has 2 significant figures.

Density

• Density Formula: $\text{Density} = \frac{\text{mass}}{\text{volume}}$

• Example: A metal weighing 45.42 g with a volume of 5.10 mL has a density of $8.91 \text{ g/cm}^3$.

Periodic Table and Atomic Structure

Periodic Table

• Elements are arranged by increasing atomic number.

• Groups (columns) share similar chemical properties.

• Periods (rows) indicate increasing energy levels.

Isotopes

• Isotopes: Atoms of the same element with different numbers of neutrons.

• Example: $^{12}C$ and $^{13}C$ are isotopes of carbon.

Atomic Mass and Abundance

• Atomic mass is calculated using the weighted average of isotopic masses and their abundances.

• Example: Silver has isotopes Ag-107 and Ag-109 with respective abundances; atomic mass is $108.19$ amu.

Chemical Formulas and Nomenclature

Empirical and Molecular Formulas

• Empirical Formula: The simplest whole-number ratio of atoms in a compound.

• Molecular Formula: The actual number of atoms of each element in a molecule.

• Example: If the empirical formula is CH2 and the molar mass is 72.18 g/mol, the molecular formula is C6H12.

Percent Composition

• Percent composition is the percentage by mass of each element in a compound.

• Example: Lithium in Li3PO4 is 17.98% by mass.

Balancing Chemical Equations

• Balanced equations have equal numbers of each atom on both sides.

• Example: $2Al(OH)_3 + 3NH_4^+ + 3H_2PO_4^- \rightarrow AlPO_4 + 3NH_4Cl + 6H_2O$

Stoichiometry and Chemical Reactions

Stoichiometric Calculations

• Use molar ratios from balanced equations to calculate amounts of reactants and products.

• Example: If 50.0 g S and 105.0 g F2 react, the excess reactant is 20.5 g S.

Percent Yield

• Percent Yield Formula: $\%\text{yield} = \frac{\text{actual yield}}{\text{theoretical yield}} \times 100$

• Example: The percent yield for a reaction producing 5.00 g Ca(OH)2 from 12.0 g Ca is 22.5%.

Organic Chemistry Basics

Functional Groups

• Ketones: Organic compounds with a carbonyl group (C=O) bonded to two carbon atoms.

• Example: The structure shown is a ketone.

Sample Table: Fractional Subcharges

This table provides common fractional subcharges for calculations. (Additional info: Table entries are used for multiplying by specific factors in stoichiometric and atomic mass calculations.)

Fractional Subcharge	Multiply by This
1/2	0.5
1/3	0.333
1/4	0.25
1/5	0.2
1/6	0.167
1/7	0.143
1/8	0.125
1/9	0.111
1/10	0.1

Practice Problems and Applications

Sample Calculations

• Calculate the number of atoms in a given mass using Avogadro's number.

• Determine empirical and molecular formulas from percent composition and molar mass.

• Balance chemical equations and use them for stoichiometric calculations.

Periodic Table Reference

The periodic table is provided for reference during calculations and for identifying element properties.

Summary of Key Terms

• Atom: Smallest unit of an element retaining its chemical properties.

• Element: Substance consisting of one type of atom.

• Compound: Substance formed from two or more elements chemically bonded.

• Isotope: Atoms of the same element with different neutron numbers.

• Mole: Amount of substance containing $6.022 \times 10^{23}$ entities.

• Empirical Formula: Simplest ratio of elements in a compound.

• Molecular Formula: Actual number of atoms in a molecule.

• Percent Yield: Ratio of actual to theoretical yield in a reaction.

Exam Strategies

• Show all work for calculations to receive full credit.

• Use significant figures appropriately in all answers.

• Refer to the periodic table and provided equations for problem-solving.