Terminology

5. A chemical process in which an atom or molecule gains electrons, often associated with a decrease in oxidation state.
7. A numerical factor in a chemical equation that indicates the number of molecules or moles of a substance involved in the reaction.
12. Substances that undergo a chemical change in a reaction; they are present at the beginning of the reaction.
13. A chemical reaction in which one element replaces another in a compound.
14. Notations used in chemical equations to indicate the physical state of the substances involved (e.g., (s) for solid, (l) for liquid, (g) for gas, (aq) for aqueous solution).
15. A type of chemical reaction in which two or more simple substances combine to form a more complex product.
17. A chemical reaction that occurs when a substance reacts rapidly with oxygen, producing heat and light; typically involves hydrocarbons.
18. A unit used in chemistry to measure the amount of a substance; one mole contains approximately 6.022 \times 10^{23} particles (atoms, molecules, etc.).
19. A chemical equation in which the number of atoms of each element is equal on both sides of the equation, satisfying the law of conservation of mass.
20. A type of chemical reaction in which a complex substance breaks down into simpler products.

1. A chemical reaction in which the ions of two compounds exchange places in an aqueous solution to form two new compounds.
2. A fundamental principle stating that mass is neither created nor destroyed in a chemical reaction; the total mass of reactants equals the total mass of products.
3. A symbolic representation of a chemical reaction, showing the reactants and products along with their quantities.
4. A chemical process in which an atom or molecule loses electrons, often associated with an increase in oxidation state.
6. Substances formed as a result of a chemical reaction; they are present at the end of the reaction.
8. A substance that increases the rate of a chemical reaction without being consumed in the process.
9. A type of chemical reaction that releases heat to its surroundings, resulting in an increase in temperature.
10. The calculation of reactants and products in chemical reactions based on the balanced chemical equation.
11. A small number written after an element's symbol in a chemical formula that indicates the number of atoms of that element in a molecule.
16. A type of chemical reaction that absorbs heat from its surroundings, resulting in a decrease in temperature.