why does mass change during a chemical reaction process?

Question

Hey , i'm doing this chem prac , and i cant figure out the answer to this bonus question.

The prac im doing is basically about the Law Of Conservation of mass, by mixing Silver nitrate with Potassium Iodide to form Potassium Nitrate + Silver Iodide, weighing them before and after. (i understand the law of conservation of mass and everything, i got the same weights before and after)

But i cant work out the answer to this question:
When the flask containing the Silver nitrate with Potassium Iodide is placed on the weighing balance the moment the reaction started, it is noticed that the mass fluctuates and drops during the reaction process. Why does this happen? (state the reasoning behind and what is happening on atomic/intermolecular level)

I'm thinking it has something to do with atoms breaking rejoining and vibrating against each other, causing the mass to change? Can someone explain to mewhats happenin on an ATOMIC level, containing KEY TERMS and important details?? Thanks

Answer 1

Mass changes only happen where matter is created or coverted from/to energy. . This is a sub atomic particle event. Is the reaction exothermic or endothermic ?? If so, how does your measuring system react to those changes. If it is a solution, is there evaporation ? As you pour in reagents, do you disturb the balance because of the effect of the weight of the stuff you dump in ?Think beyond the obvious

Answer 2

The only way the mass could change (temporarily) is if the reaction was exothermic. Hot objects appear to weigh less than cold objects, because they heat up the column of air above them which becomes less dense than the surrounding air. But as the reaction mixture cools down, so should the mass return to exactly the same as it was before.

No gases are given off in this reaction - it's a straightforward precipitation reaction.

Answer 3

Absolutely the mass did not change. Not a bit. Even the exact count of the atoms did not change. You have a measurement error, here. Unless, of course, gasses were liberated in the reaction. My chem is a little too old to remember that reaction exactly, but if no H or no O or no I is liberated, then your measurement is the culprit.

Answer 4

Law of conservation of mass holds at all time during any reaction and at any stage of the reaction....
"As you know, weight of any body is related to the gravitational force, which is dependent on the distance and angle from the earth"
In your case during reaction of the two specified chemicals, there will be enough vibration in the flask or you can say that molecules of both chemicals are dancing with each other, and both distance and angle are changing with respect to the molecules.

hope so , now you got the clarification.

Answer 5

Endothermic and exothermic chemical reactions could do the rearrangements of molecules and atoms. The Einstein equation has to do with the rearrangement of protons and neutrons.