Chemistry Practice

Sour-tasting substances that can 'burn'—they give away hydrogen ions.

The 'hill' reactants must climb over before the reaction can proceed.

Atoms can't appear or disappear — every atom on the left must show up on the right.

Slippery substances that can neutralize acids—they remove hydrogen ions.

A buffer acts like a chemical shock absorber for pH.

A helper that makes the reaction easier but isn't used up in the process.

A recipe that shows what goes in, what comes out, and in what amounts.

The reaction is still happening both ways, but the amounts stay constant.

Old bonds break, new bonds form. You end up with different stuff than you started with.

Molecules must hit each other the right way and hard enough for bonds to break.

Matter can't vanish or appear from nothing. What goes in equals what comes out.

Separate the oxidation and reduction halves, connect them with a wire and ion path, and the reaction can do electrical work.

Electrochemistry connects chemical reactions and electrical energy in both directions.

Salt dissolved in water breaks into charged particles (ions) that carry electric current.

Instead of getting electricity from chemistry, you spend electricity to make chemistry happen.

The reaction needs heat to proceed — you can feel the surroundings get colder as it runs.

Enthalpy change tells you how much heat a reaction releases or absorbs at constant pressure: $\Delta H < 0$ means heat is released (exothermic, the surroundings warm up) and $\Delta H > 0$ means heat is absorbed (endothermic).

K is the scoreboard at the end of the game — it tells you which side won. Large K means products dominate; small K means reactants dominate.

The reaction gives off heat—you can feel the surroundings get warmer as it proceeds.

Push on equilibrium, and it pushes back. Add something, and the system uses it up.

Acid + Base → they cancel each other out, making water and salt.

Giving away electrons. Originally meant 'gaining oxygen' but it's broader.

A number that tells you: acid (low), neutral (7), base (high).

What you end up with after the reaction — the new stuff that gets made from the ingredients.

What you start with — the ingredients that get used up to make something new.

How quickly the reaction happens—from instant explosion to years of rusting.

One thing loses electrons (oxidized), another gains them (reduced).

Grabbing electrons. The charge gets 'reduced' (becomes more negative).

A salt is the ionic compound left over after the acid-base part of a reaction has made water.

Properties you can only discover by trying to react the substance — they describe what it can become, not what it looks like.

Density answers 'how heavy is this for its size?' A small lead ball is heavier than a large foam ball — lead is denser.

Different parts look or behave differently. One spoonful is not the same as another.

It looks the same everywhere. You can't see the separate parts, even under a microscope.

Everything you can touch, see, or weigh is matter. Air is matter too — you just can't see it.

You can see the different parts. A salad, trail mix, or sand in water — the ingredients don't blend together evenly.

Different substances have different properties — use those differences to pull them apart. Heavy things sink, liquids evaporate at different temperatures.

Everything is made of tiny particles that are always moving. How fast they move and how tightly they're held together explains solids, liquids, and gases.

Add enough heat and a solid melts to liquid, then boils to gas. Remove heat and the reverse happens.

Properties you can detect just by looking, touching, or measuring — without turning the substance into something else.

Every particle in a pure substance is the same. Pure water is all H₂O — no exceptions.

The thing that 'disappears' when you dissolve it — like sugar dissolving in tea. The sugar is the solute.

The 'background' substance that the solute dissolves into. Water is called the 'universal solvent' because it dissolves so many things.

Particles packed tight and vibrating = solid. Particles sliding past each other = liquid. Particles flying freely = gas.

What you really got after doing the reaction.

The number under each element on the periodic table—a weighted average of all its isotopes.

More gas particles need more space if temperature and pressure stay the same.

A mind-bogglingly large number — but it's exactly the right size to make atomic counting practical.

Squeeze a gas into less space and it pushes back harder.

Warmer gas spreads out more when it is free to expand.

How 'strong' a solution is—more solute in the same volume = more concentrated.

Watering down a drink—same amount of flavor, more liquid, weaker taste.

The reduced fraction of atoms—smallest numbers that show the ratio.

If one ingredient runs out first, the other one is left over.

How gases behave when you squeeze them, heat them, or add more.

Grams tell you how heavy something is. A paperclip is about 1 gram. Moles tell you how many particles you have—a completely different question.

If you have 10 buns and 5 patties, you can only make 5 burgers—patties are limiting.

How much one mole weighs. For elements, it's the number on the periodic table.

A 'chemist's dozen'—a huge number that makes atom-counting practical.

The real count of atoms, not just the ratio — it tells you exactly what the molecule contains.

What fraction of the compound's total weight is made up by each element inside it.

How much of the possible product you actually got — 100% is perfect, real reactions are always less.

How much can dissolve before no more will. Sugar: high solubility. Sand: zero.

One substance completely mixed into another—you can't see separate parts.

Using the recipe (balanced equation) to figure out how much of each ingredient you need.

The perfect-world result — the most product you could possibly get if nothing is lost or wasted.

Slowly adding a known solution to an unknown one until the reaction is just complete — the volume used reveals the concentration.

Burning. When something burns, it's reacting with oxygen and releasing energy as heat and light.

The reverse of synthesis — taking apart a complex structure into simpler pieces.

Two couples swap partners at a dance — each positive ion pairs with the other's negative ion.

Chemical formulas are the 'spelling' of chemistry — they tell you exactly which atoms and how many of each are in a compound.

Strip away the bystanders. Some ions just float around doing nothing — the net ionic equation shows only the ones that actually react.

Chemistry has a naming system so that every compound gets exactly one name and every name points to exactly one compound — like a universal address system.

An imaginary 'electron bookkeeping' system. If an atom 'owns' more electrons than usual, its oxidation number is negative; fewer means positive.

Mix two clear solutions and a solid appears 'out of nowhere' — the ions combine to form a compound that won't dissolve.

A bully element kicks a weaker one out of its compound — like a stronger player replacing a weaker one on a team.

Building something bigger from smaller parts — like assembling LEGO bricks into a structure.

The tiny building blocks everything is made of. Break matter down far enough, you get atoms.

The atom's ID number — $Z = 6$ always means carbon, no matter what else changes.

The 'glue' that holds atoms together, made by sharing or transferring electrons.

Elements joined together to make something new with different properties.

Atoms hold electrons together like kids sharing a toy. Neither gives it away.

The particles that do the 'dancing'—they're what's involved in bonding and reactions.

Electrons fill energy levels like seats in a theatre — front rows first, then moving back.

Electrons live in 'floors' around the nucleus. Lower floors fill first.

How 'greedy' an atom is for electrons. Fluorine is most greedy.

A pure substance that can't be broken down chemically. Gold is gold, oxygen is oxygen.

The functional group is the part of an organic molecule that most strongly controls how it behaves.

Radioactive samples do not lose the same amount each time; they lose the same fraction each time.

Hydrocarbons are the simplest organic molecules: just carbon plus hydrogen.

When hydrogen is attached to a very electronegative atom, nearby molecules feel an unusually strong attraction.

These are the attractions between neighboring particles, not the bonds holding each particle together.

An atom that's not neutral—it has more or fewer electrons than protons.

One atom gives electrons away; another takes them. Opposites attract.

Same element, slightly different weight. Chemically identical, but different mass.

A map showing how electrons are arranged and shared between atoms.

How heavy the nucleus is — each proton and neutron contributes about 1 atomic mass unit.

Metal atoms share mobile electrons across the whole solid instead of keeping them between fixed pairs of atoms.

Things stirred together but not joined. Each substance keeps its own properties.

Electron pairs repel each other, pushing atoms as far apart as possible — this determines the molecule's shape.

Even if individual bonds are polar, the molecule can be nonpolar if the dipoles cancel out symmetrically.

Atoms stuck together. Water ($\text{H}_2\text{O}$) is one molecule with 3 atoms.

The glue that helps hold the nucleus together without adding charge.

8 is the magic number. Atoms 'want' a full outer shell like noble gases.

Carbon can build huge families of compounds, so chemists study those compounds as a major branch of chemistry.

A map of all elements organized so similar ones are in the same column.

As you move across or down the periodic table, element behavior changes in regular, trackable ways.

Two atoms sharing electrons, but one pulls harder — like a tug of war where one side is stronger.

A polymer is like a long molecular chain built from many repeating links.

The identity badge of an atom—how many protons determines what element it is.

Some nuclei are unstable and shed particles to reach a more stable state — like a unstable pile of blocks rearranging.

The electrons that 'reach out' to other atoms. These do the bonding.