POV: I told a chemistry joke in class, but there was no reaction

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Across
  1. 1. A combination of two or more substances in which each keeps its own properties,
  2. 4. of conservation of mass; The mass of substances before a chemical reaction is the same as the mass of substances after the reaction,
  3. 5. The small number beside a chemical symbol, letting you know how many atoms are in the reaction
  4. 7. A solid formed from two or more elements, with fixed proportions,
  5. 9. change; the type of change where the molecules chemical composition does not change
  6. 11. A chemical reaction in which heat is absorbed from the surroundings,
  7. 14. The number of atoms of each element must be the same on both sides of a balanced chemical equation,
  8. 15. A substance formed from two or more elements that are chemically combined,
Down
  1. 2. Substance that takes part in a chemical reaction,
  2. 3. A type of chemical reaction in which a compound breaks down into simpler substances, Physical; The type of change where a substance changes its physical appearance, but not its chemical composition,
  3. 6. The process by which a solid turns into a liquid,
  4. 7. change; The type of change where a new substance with different properties is formed and bonds are broken,
  5. 8. A reaction in which two or more substances combine to form a new substance,
  6. 10. The smallest unit of an element that retains its properties,
  7. 12. The type of reaction that releases energy in the form of light or heat.
  8. 13. A substance that cannot be broken down into simpler substances by chemical means, made up of only one type of atom,