Chemistry question...in reactions, do the reactants weigh more, less, or the same as the product?

Question

Take for example this reaction: 2NaCl + 2H2O --> 2NaOH + Cl2 + H2

Do the reactants

weigh more because Cl2 and H2 are gases
weigh the same as the products
weigh more than the products because the reaction isn't perfect

Answer 1

Their is no loss or gain of atoms, once you balance the equation, so the products weight the same as the reactants. The fact that H2 and Cl2 are gases doesn't affect the weight of the compounds used, as long as the reaction is done in a closed container and you don't lose any.

Answer 2

You must recognize that almost no reaction actually goes to completion, and so some reactants are left over. Now, since this is so, the sum total of the reactants and products have the same mass as the original mass when only reactants are present. Gases do not weigh less per mass than solids, only per volume, so the first answer is incorrect. In a reaction which favors products, the products weigh more than the reactants at the end, as they have been made at the expense of the reactants. Since matter cannot be destroyed (only converted into energy in special cases) the same mass is present at beginning and end of any reaction, only in different forms. The question is somewhat poorly worded, but the answer they want is most likely the second one.

Answer 3

The principle of conservation of mass says that the products of a reaction weigh the same as the reactants.

However, when you react salt with water, you don't get the NaOH or the gasses as the above equation indicates. The salt simply dissolves. Dissolving is a physical reaction, not a chemical one.

Answer 4

They weigh the same, assuming all the reactants become products. To verify, just add up the molecular weights on either side of the reaction.

Answer 5

Weigh the same as the products according to Laplace Mass conservation Law.

Good luck!

Answer 6

The reactants and products should weigh exactly the same assuming 100% yield.

Answer 7

in chemistry we compare molar amounts not weights. a reaction having 100% yield can seem to be missing a lot of mass unless you take into account the stoichiometry.

Answer 8

In this case, none of the above. This reaction does not happen. If you add NaCl to H2O, you get salty water. You do not get sodium hydroxide, chlorine, and hydrogen.

Answer 9

Conservation of mass! They weigh the same.

Answer 10

Think about balancing a checkbook when you balance reactions, what goes in, must come out.