Why is the total mass of the products of a chemical reaction is equal to the total mas of the reactants?

Answer 1

This isn't true. The mass of reactants will equal mass of products in a closed system where gasses cannot enter or escape, but the mass can decrease if a gas is formed that escapes into the atmosphere (for example, hydrogen from your reactants is transformed into hydrogen or oxygen gas which escape into the room) or even INCREASE of the reaction draws in gas from the atmosphere which is incorporated into the product. There might even be an increase in mass if water vapor from the air ends up entering into the reaction.

The equation for the reaction will always balance because of conservation of mass, but where that mass ends up can mean that the final weights to NOT remain the same. A closed system doesn't allow for entry or exit of additional mass, but an open system might.

Answer 2

Yes, in a non-nuclear chemical reaction, the mass of the products is equal to the mass of the reactants. However, the mass of the products and reactants in nuclear reactions can be different. The mass in this case is transformed into energy.

Answer 3

In a chemical change, all the atoms in the reactants end up in the products. Chemical changes involve rearranging atoms to form different substances, atoms cannot be conjured up from nothing or disappear into thin air!

So, the mass of the reactants is always equal to the mass of the products.

However, in some situations, it can look otherwise. For example, when magnesium burns (reacts with oxygen) the mass of the magnesium oxide produced is more than the magnesium you started with. But of course, when you weighed the magnesium, you didn't weigh the oxygen gas from the air. If you weighed the magnesium atoms and the oxygen molecules involved, the mass would be equal to the mass of the magnesium oxide product.

As another example, consider marble chips (calcium carbonate) reacting with hydrochloric acid. If you weigh the beaker containing the reactants the mass will decrease over time, until the reaction is complete. Of course we can account for this mass loss, because carbon dioxide gas is produced and in an unsealed beaker this will escape into the atmosphere and the mass will decrease. If we did not allow the gas to escape the mass would not change.

So, the mass of what you start with is always equal to the mass of what you end up with. You always have the same atoms on both sides of a chemical equation (although when gases are involved it can look like mass is lost or gained) they are just rearranged!

Answer 4

Yes. The only time mass is destroyed (converted to energy) is in nuclear reactions. In chemical reactions mass is conserved (same before as after)

Answer 5

Yes, that is what defines a "balanced" equation. Mass like energy is always conserved.

Answer 6

They have to equal because if they don't then the whole planet will die.

Answer 7

no atom is lost in a chemical reaction and therefore the weight will be equal

Answer 8

The chemicals that react are called reactants; the chemicals which result from a reaction are called products. And yes, the mass of the reactants will equal the mass of the products.

Answer 9

yes