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List four observations that indicate that a chemical reaction may be taking place

Remember to use the proper number of significant figures and leading zeros in all calculations. gelatin has a density of 1.27 g/cm³. if you have a blob of gelatin dessert that fills a 2.0 liter bottle, what is its mass? 2540 g2500 g3.9 x 10-43.937x 10-4

Assume that 13.5 g solid aluminum (al) react with hcl to produce solid aluminum chloride (alcl3) salt and gaseous hydrogen (h2) at standard temperature and pressure.