13. Contrast endothermic and exothermic reactions (Unit 1). 14. _ are the basic unit of matter. (Unit 1)
15. _ are pure substances made up of only one type of atom (i. e. hydrogen H) while _ are pure substances that are made up of two or more types of atoms in a specific ratio (i. e. carbon dioxide CO2). (Unit 1)
16. When a _ change occurs, the resulting substances have new/different properties. (Unit 1)
17. Contrast erosion and weathering. (Unit 2)

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