Rucete ✏ SAT Chemistry In a Nutshell
1. Introduction to Chemistry
Chemistry begins with understanding matter and its interactions. This chapter outlines core skills like identifying types of matter, distinguishing between chemical and physical changes, working with SI units, applying scientific notation, and recognizing how energy flows during reactions. These concepts form the foundation of chemistry knowledge for the SAT.
Matter
Matter is anything that has mass and occupies space. Its mass resists changes in motion (inertia).
Weight is mass influenced by gravity. While weight can change, mass remains constant.
Density is the ratio of mass to volume (density = m/V) and helps compare how much space substances of equal mass occupy.
Common volume units include cm³, mL, and L, while mass is typically measured in grams (g).
States of Matter
Solid: Definite shape and volume.
Liquid: Definite volume but takes the shape of its container.
Gas: No definite shape or volume, expands to fill container.
Matter can change states when heat is added or removed (e.g., ice → water → steam).
Classification of Matter
Pure substances include elements and compounds.
Elements consist of only one kind of atom (e.g., gold, nitrogen).
Compounds are made of atoms of different elements in fixed ratios (e.g., H₂O, CO₂).
Mixtures are physical combinations of substances that can vary in composition and be separated by physical means.
Homogeneous mixtures have uniform composition (e.g., sugar in water); heterogeneous mixtures do not (e.g., marble).
Properties of Matter
Physical properties can be observed without changing substance identity (e.g., color, melting point, solubility).
Chemical properties describe how substances react (e.g., iron rusting, sodium reacting with water).
Changes in Matter
Physical changes affect form or appearance without altering composition (e.g., melting ice, cutting wood).
Chemical changes result in new substances with different properties and involve energy changes.
Exothermic reactions release energy (ΔH < 0); endothermic reactions absorb energy (ΔH > 0).
Activation energy is required to initiate a chemical reaction.
Conservation Laws
Law of Conservation of Mass: Matter is not created or destroyed in chemical reactions.
Law of Conservation of Energy: Energy is conserved in all physical and chemical changes.
Law of Conservation of Mass and Energy (Einstein): Under special conditions, mass and energy can convert into each other (E=mc²).
Scientific Method
Scientific investigations follow a process: observation → hypothesis → experimentation → model building.
Hypotheses are testable “if...then” statements that are revised based on results.
Models help explain phenomena using visual, verbal, or mathematical means.
Measurement and SI Units
Observations are qualitative (descriptive) or quantitative (measured).
SI (International System) units are standard: meter (m), kilogram (kg), second (s), mole (mol), kelvin (K), etc.
Prefixes like kilo- (×1000) or milli- (÷1000) adjust unit sizes based on powers of 10.
Scientific Notation
Used to express very large/small numbers with powers of 10 (e.g., 3.6 × 10⁶).
In multiplication/division: match significant figures.
In addition/subtraction: match decimal places.
Dimensional Analysis
Also called the factor-label method, used for unit conversions.
Set up conversion factors as fractions to cancel out units and arrive at the desired one.
Precision, Accuracy, and Uncertainty
Accuracy: Closeness to the true value.
Precision: Repeatability of measurements.
Uncertainty comes from instrument limits and human estimation.
Always estimate the last digit in a measurement—it is considered uncertain.
Significant Figures
Include all known digits plus one estimated digit.
In multiplication/division: answer must match the quantity with the fewest significant figures.
In addition/subtraction: answer must match the quantity with the fewest decimal places.
In a Nutshell
This chapter introduces the core principles of chemistry: types and properties of matter, physical and chemical changes, energy in reactions, SI units and measurement, scientific notation, dimensional analysis, and how scientific thinking is applied. These foundational ideas are essential for understanding and solving SAT Chemistry problems.