How to Use This Glossary
This chapter is a beginner-friendly glossary of essential chemistry terms you will see repeatedly in problems, lab directions, and everyday explanations of chemical change. It focuses on vocabulary you need to read chemistry clearly without re-teaching topics already covered earlier (such as atomic structure, bonding types, naming compounds, balancing equations, and acids/bases).
How to study with this glossary:
Step 1: Read the definition and say it in your own words.
Step 2: Notice the “how it shows up” clue (what you’d look for in a question or lab).
Step 3: Use the example to connect the word to a real situation.
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Step 4: Practice by writing one sentence using the term correctly.
States, Mixtures, and Solution Vocabulary
Phase
Meaning: A physically uniform region of matter with consistent properties (like a single solid region, a single liquid region, or a single gas region). A system can have one phase or multiple phases.
How it shows up: When you see layers, chunks, bubbles, or separate regions, you likely have multiple phases.
Example: Ice floating in water is two phases (solid ice and liquid water) even though it is the same substance.
Homogeneous mixture
Meaning: A mixture that is uniform throughout; you cannot see different parts with the naked eye.
How it shows up: “Evenly mixed,” “single phase,” “same composition everywhere.”
Example: Saltwater after the salt has fully dissolved.
Heterogeneous mixture
Meaning: A mixture that is not uniform; different parts have different compositions.
How it shows up: Visible pieces, layers, or settling over time.
Example: Sand in water; the sand settles and can be seen.
Solution
Meaning: A homogeneous mixture in which one substance is dispersed at the particle level in another.
How it shows up: Often described by concentration (like “0.50 M”) or by “dissolved in.”
Example: Vinegar is a solution of acetic acid in water.
Solvent
Meaning: The component of a solution present in the larger amount; it does the dissolving.
How it shows up: In aqueous solutions, water is the solvent.
Example: In saltwater, water is the solvent.
Solute
Meaning: The component of a solution present in the smaller amount; it gets dissolved.
How it shows up: The substance you add to the solvent.
Example: In saltwater, salt is the solute.
Aqueous (aq)
Meaning: Dissolved in water. In chemical notation, “(aq)” indicates the substance is in an aqueous solution.
How it shows up: In equations and lab instructions: NaCl(aq), HCl(aq).
Example: “Add AgNO3(aq)” means add silver nitrate dissolved in water.
Miscible / Immiscible
Meaning: Miscible liquids mix completely to form one phase; immiscible liquids do not and form layers.
How it shows up: Layer formation is a strong clue of immiscibility.
Example: Ethanol and water are miscible; oil and water are immiscible.
Suspension
Meaning: A mixture where solid particles are dispersed in a liquid but are large enough to settle out over time.
How it shows up: Cloudy mixture that separates on standing; can often be filtered.
Example: Muddy water.
Colloid
Meaning: A mixture with dispersed particles that are smaller than in a suspension; they do not settle quickly and can scatter light.
How it shows up: “Tyndall effect” (a visible beam of light through the mixture).
Example: Milk is a colloid.
Concentration
Meaning: A measure of how much solute is present in a given amount of solution (or solvent).
How it shows up: Words like “dilute,” “concentrated,” or units like molarity (M), percent, ppm.
Example: A sports drink is more concentrated than plain water because it contains dissolved sugars and salts.
Dilution
Meaning: Lowering concentration by adding more solvent.
Practical step-by-step:
Step 1: Decide the final concentration you want.
Step 2: Measure a known volume of the original (more concentrated) solution.
Step 3: Add solvent to reach the new total volume.
Step 4: Mix thoroughly so the solution is uniform.
Example: Making a weaker cleaning solution by adding water to a concentrated product.
Energy, Heat, and Stability Vocabulary
Energy
Meaning: The ability to do work or transfer heat. In chemistry, energy changes often accompany changes in particle arrangement.
How it shows up: Temperature changes, heat flow, light emission, electrical work.
Heat (q)
Meaning: Energy transferred because of a temperature difference. Heat flows from warmer to cooler objects.
How it shows up: Calorimetry problems, “released heat,” “absorbed heat.”
Temperature
Meaning: A measure related to the average kinetic energy of particles in a sample.
How it shows up: Thermometers, heating/cooling curves, reaction rate discussions.
Endothermic / Exothermic
Meaning: Endothermic processes absorb heat from surroundings; exothermic processes release heat to surroundings.
How it shows up: A temperature drop in the surroundings suggests endothermic; a temperature rise suggests exothermic.
Example: Instant cold packs are endothermic; hand warmers are exothermic.
Enthalpy (H) and ΔH
Meaning: Enthalpy is a quantity used to track heat changes at constant pressure. ΔH is the change in enthalpy for a process.
How it shows up: Thermochemistry statements like “ΔH = −57 kJ” (exothermic) or “ΔH = +90 kJ” (endothermic).
Activation energy (Ea)
Meaning: The minimum energy barrier that must be overcome for a reaction to proceed.
How it shows up: Reaction rate explanations; why some reactions need heating or a spark.
Example: Gasoline doesn’t burn without a spark because the activation energy must be supplied.
Catalyst
Meaning: A substance that increases reaction rate by providing an alternative pathway with lower activation energy, without being consumed overall.
How it shows up: “Speeds up,” “not used up,” “enzyme” (biological catalyst).
Example: Catalytic converters use catalysts to help convert harmful exhaust gases into less harmful ones.
Equilibrium (dynamic equilibrium)
Meaning: A state in which forward and reverse processes occur at the same rate, so macroscopic amounts remain constant even though particles keep changing.
How it shows up: Reversible reactions, constant concentrations over time, “⇌” symbol.
Example: In a sealed bottle of soda, dissolved CO2 and CO2 gas can reach equilibrium.
Le Châtelier’s principle
Meaning: If a system at equilibrium is disturbed (by changing concentration, pressure, or temperature), it shifts in the direction that reduces the disturbance.
Practical step-by-step (predicting a shift):
Step 1: Identify what changed (added reactant, removed product, increased pressure, etc.).
Step 2: Treat the change as “stress.”
Step 3: Predict the direction that would counteract it (consume what was added, replace what was removed).
Step 4: Translate that direction into “shift left” or “shift right.”
Example: If you add more reactant to an equilibrium mixture, the system tends to shift toward products to use up some of the added reactant.
Reaction Speed and Collision Vocabulary
Reaction rate
Meaning: How fast reactants are converted into products, often expressed as change in concentration per time.
How it shows up: “Faster/slower,” graphs of concentration vs. time, factors affecting rate.
Collision theory
Meaning: Particles must collide with enough energy and proper orientation to react.
How it shows up: Explanations involving temperature, concentration, surface area, catalysts.
Rate law
Meaning: An equation that relates reaction rate to reactant concentrations raised to powers determined experimentally.
How it shows up: “Rate = k[A]^m[B]^n” and questions about how rate changes when concentration changes.
Rate constant (k)
Meaning: A proportionality constant in a rate law; depends on temperature and the specific reaction.
How it shows up: Units vary depending on reaction order; increases with temperature for most reactions.
Reaction mechanism
Meaning: A proposed step-by-step sequence of elementary steps that explains how a reaction occurs.
How it shows up: Multi-step reactions, intermediates, and rate-determining step discussions.
Intermediate
Meaning: A species formed in one step of a mechanism and consumed in a later step; it does not appear in the overall balanced equation.
How it shows up: Appears in mechanism steps but cancels out when steps are added.
Rate-determining step
Meaning: The slowest step in a mechanism; it limits the overall reaction rate.
How it shows up: “Bottleneck” step; often linked to the activation energy barrier.
Quantities Used in Chemical Calculations
Mole (mol)
Meaning: A counting unit for particles (atoms, molecules, ions), like a “chemist’s dozen,” but much larger.
How it shows up: Converting between mass and number of particles; formulas and stoichiometry setups.
Avogadro’s number
Meaning: The number of particles in 1 mole: 6.022 × 1023.
How it shows up: Converting moles to particles and vice versa.
Molar mass
Meaning: Mass of 1 mole of a substance, usually in g/mol.
How it shows up: Mass-to-mole conversions in calculations.
Stoichiometric coefficient
Meaning: The number in front of a formula in a chemical equation; it indicates relative amounts (in moles) of reactants and products.
How it shows up: Mole ratios in reaction calculations.
Limiting reactant
Meaning: The reactant that is used up first; it limits how much product can form.
How it shows up: “Which reactant runs out?” “How much product forms?”
Excess reactant
Meaning: Any reactant left over after the limiting reactant is consumed.
How it shows up: “How much remains?” problems.
Theoretical yield
Meaning: The maximum amount of product predicted by stoichiometry, assuming the reaction goes perfectly and completely.
How it shows up: Compared to actual yield to evaluate efficiency.
Actual yield
Meaning: The amount of product actually obtained in an experiment.
How it shows up: Measured mass or moles of product collected.
Percent yield
Meaning: A measure of efficiency: (actual yield ÷ theoretical yield) × 100%.
Practical step-by-step:
Step 1: Calculate theoretical yield from the limiting reactant.
Step 2: Record the actual yield from the experiment.
Step 3: Divide actual by theoretical.
Step 4: Multiply by 100 to convert to percent.
Example: If theoretical yield is 10.0 g and actual yield is 8.5 g, percent yield = (8.5/10.0)×100% = 85%.
Significant figures
Meaning: A way to communicate measurement precision using digits that are meaningful based on the measuring tool.
How it shows up: Rounding rules in calculations; lab reports.
Practical step-by-step (quick rounding workflow):
Step 1: Identify how many significant figures your final answer should have (often based on the least precise measurement used).
Step 2: Keep extra digits during intermediate steps to avoid rounding too early.
Step 3: Round only at the end to the correct number of significant figures.
Laboratory and Data Vocabulary
Accuracy
Meaning: How close a measurement is to the true or accepted value.
How it shows up: “Is it correct?” comparisons to a known standard.
Precision
Meaning: How close repeated measurements are to each other (repeatability), regardless of whether they are correct.
How it shows up: Tight clustering of repeated trials.
Systematic error
Meaning: A consistent bias that shifts results in one direction (too high or too low), often due to calibration or method issues.
How it shows up: All trials are off by about the same amount.
Example: A balance that reads +0.10 g when empty causes all masses to be too high.
Random error
Meaning: Unpredictable variation from trial to trial due to small uncontrollable factors.
How it shows up: Scatter in repeated measurements.
Calibration
Meaning: Adjusting or checking an instrument against a known standard to improve accuracy.
How it shows up: “Calibrate the pH meter,” “zero the balance.”
Control variable
Meaning: A factor kept constant so you can isolate the effect of the variable you are testing.
How it shows up: Experimental design and fair testing.
Independent variable / Dependent variable
Meaning: The independent variable is what you change on purpose; the dependent variable is what you measure as the outcome.
How it shows up: Graphs: independent variable on the x-axis, dependent on the y-axis (common convention).
Safety Data Sheet (SDS)
Meaning: A standardized document describing chemical hazards, safe handling, storage, and first aid.
How it shows up: Lab prep and safety checks before using unfamiliar chemicals.
Hazard vs. risk
Meaning: Hazard is the inherent potential to cause harm; risk is the likelihood of harm under specific conditions of use.
Example: A concentrated corrosive chemical has high hazard; risk can be reduced with goggles, gloves, and proper procedures.
More Terms You’ll See in Everyday Chemistry Language
Oxidation / Reduction (Redox)
Meaning: Oxidation and reduction are paired processes involving electron transfer. Oxidation is loss of electrons; reduction is gain of electrons. A redox reaction includes both.
How it shows up: Batteries, corrosion, combustion, and many metal reactions.
Memory aid: OIL RIG (Oxidation Is Loss, Reduction Is Gain).
Oxidizing agent / Reducing agent
Meaning: The oxidizing agent causes another species to be oxidized (it gets reduced). The reducing agent causes another species to be reduced (it gets oxidized).
How it shows up: Identifying “who gives electrons” and “who takes electrons” in redox problems.
Electrolyte
Meaning: A substance that produces ions in solution and therefore conducts electricity.
How it shows up: Conductivity discussions, batteries, salt solutions.
Example: Salt dissolved in water forms ions and makes the solution conductive.
Nonelectrolyte
Meaning: A substance that dissolves without forming ions (or forms very few), so the solution conducts poorly.
Example: Sugar dissolved in water does not produce ions, so it is a nonelectrolyte solution.
Precipitate
Meaning: A solid that forms from a solution during a reaction and separates from the liquid.
How it shows up: Cloudiness or solid formation after mixing two clear solutions; written as (s) in equations.
Example: Mixing certain ionic solutions can produce an insoluble solid that settles.
Solubility
Meaning: The maximum amount of a solute that can dissolve in a given amount of solvent at a specific temperature (and sometimes pressure).
How it shows up: “Solubility curves,” “saturated solution,” precipitate forming when too much solute is added.
Saturated / Unsaturated / Supersaturated
Meaning: Unsaturated means more solute can dissolve; saturated means at the maximum; supersaturated means more than the usual maximum is dissolved (unstable and can crystallize suddenly).
Example: A supersaturated sugar solution can form crystals when disturbed or seeded with a sugar crystal.
Volatile
Meaning: A substance that evaporates easily (has a relatively high tendency to enter the gas phase).
How it shows up: Strong smell, rapid evaporation, safety notes about vapors.
Inert
Meaning: Chemically unreactive under specified conditions.
How it shows up: “Inert atmosphere” (like nitrogen or argon) used to prevent unwanted reactions.
Functional group
Meaning: A specific arrangement of atoms in an organic molecule that strongly influences its properties and typical reactions.
How it shows up: Recognizing alcohols (–OH), carboxylic acids (–COOH), amines (–NH2), etc., in organic contexts.
Polymer
Meaning: A large molecule made from repeating smaller units (monomers).
How it shows up: Plastics, fibers, rubbers; “repeat unit” diagrams.
Example: Polyethylene is a polymer made from repeating ethylene units.
Isotope
Meaning: Atoms of the same element with different numbers of neutrons (same chemical identity, different mass).
How it shows up: Average atomic mass, nuclear chemistry, tracers in medicine.
Radioactivity
Meaning: Spontaneous emission of particles or energy from an unstable nucleus.
How it shows up: Alpha, beta, gamma radiation; half-life; safety procedures.
Half-life
Meaning: The time required for half of a radioactive sample to decay.
How it shows up: Dating methods, medical isotopes, decay calculations.
Model (scientific model)
Meaning: A simplified representation used to explain and predict behavior (like diagrams, equations, or physical analogies).
How it shows up: Particle diagrams, energy diagrams, and simplified assumptions in problem-solving.
Mini Practice: Use the Terms Correctly
Practice Set A: Identify the best term
Choose the glossary term that best matches each description.
A clear mixture that looks the same everywhere after stirring: solution or heterogeneous mixture?
A solid appears after mixing two clear liquids: precipitate or solute?
A reaction speeds up when a substance is added, and that substance is still present afterward: catalyst or limiting reactant?
Repeated measurements cluster tightly but are all higher than the accepted value: precision or accuracy? systematic error or random error?
Practice Set B: Build one sentence per term
Write one correct sentence using each term. Use these as prompts:
miscible: Describe two liquids that form one layer.
activation energy: Explain why a reaction may need heating to start.
equilibrium: Describe a situation where amounts stay constant but changes still occur.
percent yield: Explain what it compares in an experiment.
Practice Set C: Quick calculation workflow (percent yield)
Use this template whenever you see a percent yield question.
1) Find limiting reactant (if needed). 2) Calculate theoretical yield (in grams or moles). 3) Use given actual yield. 4) Percent yield = (actual / theoretical) × 100%. 5) Round with correct significant figures.
