GOB Chemistry Study Guide: Fundamental Concepts, Measurements, and Matter

Introduction to Chemistry

Key Terms and Concepts

• Chemistry: The scientific study of matter, its properties, composition, and the changes it undergoes.

• Matter: Anything that has mass and occupies space.

• Chemicals: Substances with a definite composition; all matter is made up of chemicals.

Scientific Method and Reasoning

Observations, Hypotheses, Experiments, and Conclusions

• Observation: Information gathered using the senses or instruments.

• Hypothesis: A testable explanation for an observation.

• Experiment: A controlled procedure to test a hypothesis.

• Conclusion: A judgment based on the results of an experiment.

Laws vs. Theories

• Law: A statement that describes a consistently observed phenomenon, often expressed mathematically.

• Theory: A well-supported explanation of natural phenomena, based on a body of evidence.

• Comparison: Laws describe what happens; theories explain why it happens.

Mathematical Skills in Chemistry

Numbers and Calculations

• Place Value: The value of a digit based on its position in a number.

• Positive and Negative Numbers: When adding, subtracting, multiplying, or dividing, follow standard arithmetic rules for signed numbers.

• Percentages: A way to express a number as a fraction of 100. Formula: $\text{Percent} = \frac{\text{Part}}{\text{Whole}} \times 100$

• Algebraic Problem Solving: Rearranging equations to solve for unknowns.

• Graph Interpretation: Understanding and extracting information from graphical data.

Scientific Notation

• Expresses very large or small numbers as a product of a number between 1 and 10 and a power of 10. Example: $6,500 = 6.5 \times 10^3$

Measurement and Units

Metric System and SI Units

• Volume: Liter (L)

• Length: Meter (m)

• Mass: Gram (g)

• Temperature: Celsius (°C), Kelvin (K)

• Time: Second (s)

Exact vs. Measured Numbers

• Exact Numbers: Values known with complete certainty (e.g., 12 eggs in a dozen).

• Measured Numbers: Values obtained by measurement, subject to uncertainty.

Significant Figures (Sig Figs)

• Definition: Digits in a measurement that are known with certainty plus one estimated digit.

• Rules for Counting Sig Figs: All nonzero digits are significant; zeros between nonzero digits are significant; leading zeros are not significant; trailing zeros are significant if there is a decimal point.

• Rounding: Round to the correct number of sig figs based on the operation performed.

• Multiplication/Division: Result has the same number of sig figs as the measurement with the fewest sig figs.

• Addition/Subtraction: Result has the same number of decimal places as the measurement with the fewest decimal places.

Metric Prefixes and Conversions

• Common prefixes: kilo- (k, $10^3$), centi- (c, $10^{-2}$), milli- (m, $10^{-3}$), micro- (μ, $10^{-6}$), nano- (n, $10^{-9}$)

• Conversion factors are ratios used to express the same quantity in different units.

• Example: $1 \text{ km} = 1000 \text{ m}$, so $\frac{1 \text{ km}}{1000 \text{ m}}$ or $\frac{1000 \text{ m}}{1 \text{ km}}$ can be used as conversion factors.

Unit Conversions and Dimensional Analysis

• Units must cancel appropriately when converting between measurements.

• Multiple conversions may be needed in a single problem.

• Example: To convert 5.0 km to meters: $5.0 \text{ km} \times \frac{1000 \text{ m}}{1 \text{ km}} = 5000 \text{ m}$

Density and Its Applications

Definition and Formula

• Density: The mass of a substance per unit volume.

• Formula: $\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

Calculations Involving Density

• Given mass and volume, calculate density.

• Given density and one variable (mass or volume), solve for the other.

• Water displacement can be used to determine the volume of irregular objects.

Classification of Matter

Pure Substances vs. Mixtures

• Pure Substance: Matter with a fixed composition (elements and compounds).

• Mixture: Physical blend of two or more substances.

• Element: Substance made of only one type of atom.

• Compound: Substance made of two or more elements chemically combined.

• Homogeneous Mixture: Uniform composition throughout (solution).

• Heterogeneous Mixture: Non-uniform composition.

Properties and Changes of Matter

Physical vs. Chemical Properties

• Physical Properties: Can be observed without changing the substance (e.g., color, melting point).

• Chemical Properties: Describe how a substance reacts with other substances (e.g., flammability).

Physical vs. Chemical Changes

• Physical Change: Alters appearance but not composition (e.g., melting, boiling).

• Chemical Change: Produces new substances (e.g., rusting, burning).

Temperature and Energy

Temperature Scales

• Celsius (°C): Water freezes at 0°C and boils at 100°C.

• Kelvin (K): Absolute temperature scale; $K = °C + 273.15$

• Fahrenheit (°F): Water freezes at 32°F and boils at 212°F.

Conversions Between Scales

• $K = °C + 273.15$

• $°F = (°C \times \frac{9}{5}) + 32$

• $°C = (°F - 32) \times \frac{5}{9}$

Energy and Heat

• Energy: The capacity to do work or produce heat.

• SI Unit of Energy: Joule (J)

• Heat: A form of energy transferred between objects due to a temperature difference.

Calorimetry and Specific Heat

Calorimeter

• A device used to measure the amount of heat involved in a chemical or physical process.

• Works by isolating a system and measuring temperature changes.

Specific Heat

• Definition: The amount of heat required to raise the temperature of 1 gram of a substance by 1°C.

• Formula: $q = m \times c \times \Delta T$ where $q$ = heat (J), $m$ = mass (g), $c$ = specific heat (J/g°C), $\Delta T$ = change in temperature (°C)

• When two objects at different temperatures are in contact, heat flows from the hotter to the cooler object until thermal equilibrium is reached.

Changes of State and Heating Curves

States of Matter and Changes

• Change of State: Transition between solid, liquid, and gas phases.

• Terms: Melting (solid to liquid), Freezing (liquid to solid), Vaporization (liquid to gas), Condensation (gas to liquid), Sublimation (solid to gas), Deposition (gas to solid).

Heat of Fusion and Vaporization

• Heat of Fusion: Energy required to change 1 gram of a substance from solid to liquid at its melting point.

• Heat of Vaporization: Energy required to change 1 gram of a substance from liquid to gas at its boiling point.

• Calculations: $q = m \times \Delta H_{fus}$ or $q = m \times \Delta H_{vap}$

Heating and Cooling Curves

• Graphs that show temperature changes as heat is added or removed from a substance.

• Plateaus represent phase changes where temperature remains constant as energy is used to change state.

• Calculations may involve both temperature changes and phase changes.