Answer: The law of conservation of mass states that mass is neither created or destroyed, so the combined mass of all the products after the reaction will be the same as the mass of all the reactants and never more, but since the flask is not closed, the gases produced from the reaction will move into the atmosphere and the product left behind , the solids and/or liquids, will be the only products that you’ll end up weighing, meaning it’ll be less weight than the original reactants. The reason I’m interchanging weight and mass is because although weight changes with gravity, so long as the gravitational force stays constant throughout the experiment, it’s pretty much the same.
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