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Across 3. a substance that inscreases the rate of of reaction by lowering the activation-energy barrier 4. a chemical change in which a single compound is broken down into two or more simpler products 6. lowest whole-number ratio of elements in a compound 9. a compound composed of two elements 10. a chemicalequation in which mass is conserved 11. a tightly bound group of atoms that behaves as a unit and has a positive or negative charge 12. a chemical equation that does not indicate the relative amounts of reactants and products 14. the number of representative particles contained in one mole of a substance 15. the mass of a mole of any substance 18. the percent by mass of each element in a compound 19. a conversion factor derived from the coefficients of a balanced chemical equation interpreted in terms of moles 20. the portion of chemistry that deals with numerical relationships in chemical reactions 21. an ion that is not directly involved in a chemical reaction

Down 1. an ionic compound that produces hydroxide ions when dissolved in water 2. the conditions under which the volume of a gas is usually measured 5. equal volumes of gases at the same temperture and pressure equal numbers of particles 7. the amount of a substance that contains 6.02x10^23 representative particles of that substance 8. the ratio of the actual yield to the theoretical yield for a chemical reaction expressed as a percentage 13. a single atom with a positive or negative charge resulting from the loss or gain of one or more valence electrons 16. the amount of product that forms when a reaction is carried out in a laboratory 17. a compound that contains one or more hydrogen atoms and produces hydrogen ions when dissolved in water