quantile information

Question

Interpret the quantitative information in this balanced equation at the particle level, the mole level, and the mass level.  Show that the law of conservation of mass is obeyed. 

Zn(s) + 2HCl (aq)  ZnCl2 (aq) + H2 (g)

Answer 1

Hello, Madison,

I don;t see any quantitative information, so I'll assume some values as an example.

The balanced equation,

Zn(s) + 2HCl (aq)  = ZnCl₂ (aq) + H₂ (g)

should be interpreted as one atom of zinc will react with 2 molecules of HCl to form one molecule of zinc chloride and one molecule of hydrogen. What's important is that you need the ratio of actual atoms and molecule for the reaction to be balanced - the reactants are both consumed and the products produced with no loss of material, in an ideal system. The mole is a useful unit in these reactions, since it allows one to obtain the required ratios by measuring masses, instead of actually counting atoms and molecules. One mole is 6.02x10²³ particles and is easily obtained by dertermining the molar mass of the molecule and weighing out that mass to get 1 mole. Sure beats counting them one by one.

This means that we can also read the balanced equation as 1 mole of zinc reacts with 2 moles of HCL to produce 1 mole each of zinc chloride and hydrogen.

Assume we have 1 mole of zinc and 2 moles of HCl. The molar masses of each are:

Zinc: 65.38 grams/mole

HCl: 36.45 grams/mole

We produce 1 mole each of zinc chloride and hydrogen gas (H₂). The molar masses are:

ZnCl₂: 136.3 grams/mole

H₂: 2.0 grams/mole

The reactants come to a total mass of (65.38 + 2*36.45) = 138.3 grams

The products come to a total mass of (136.3 + 2) = 138.3 grams

The masses of the reactants and products are equal. This is an example of the conservation of mass. This is valid for chemical reactions, but nuclear reactions involve a small amount of mass that is converted to energy, E=mc².

Bob