Question

If 0.30 mol of Zn is added to hydrochloric acid containing 0.52 mol of HCl, how many moles of $ {{H}_{2}} $ are produced? (What is the theoretical yield of Hydrogen produced in the reaction?

Answer 1

Hint: A chemical reaction is a process that results in the chemical change of one set of chemical substances into another set of chemical substances. Chemical reactions are often defined as changes in the locations of electrons in the formation and breaking of chemical bonds between atoms, with no change in the nuclei (no change in the elements present), and may be represented using a chemical equation.

Complete answer:
Zinc and hydrogen chloride can be used to make anhydrous $ ZnC{{l}_{2}} $ :
 $ Zn\text{ }+\text{ }2\text{ }HCl\text{ }\to \text{ }ZnC{{l}_{2}}+\text{ }{{H}_{2}} $
The zinc displaces the hydrogen from hydrochloric acid in a single replacement process. The reaction produces aqueous zinc chloride and hydrogen gas as by-products. As you can see from the balancing chemical equation, the two reactants have a 1:2 mole ratio. This means that twice as many moles of hydrochloric acid as zinc metal are required for the reaction to occur.

	Zn	HCl	$ ZnC{{l}_{2}} $	$ {{H}_{2}} $
INITIAL	0.3	0.52	0	0
FINAL	0	0	0.3	x

Mole ratio of $ Zn:HCl:{{H}_{2}} $ ​ is 1:2:1
That is in $ Zn\text{ }+\text{ }2\text{ }HCl\text{ }\to \text{ }ZnC{{l}_{2}}+\text{ }{{H}_{2}} $
0.52 mol of HCl produces 0.26 grams of hydrogen gas (this is obtained by dividing 0.52 by 2)
Moles of $ {{H}_{2}} $ ​ formed is = 0.26
Note that HCl is used completely and thus it is limiting reagent.
Hence 0.26 of $ {{H}_{2}} $ grams is correct.

Note:
In a chemical process, the limiting reagent is a reactant that is completely consumed when the reaction is finished. This reagent limits the amount of product produced since the reaction cannot continue without it. Surplus reagents or excess reactants occur when one or more additional reagents are present in proportions greater than those necessary to react with the limiting reagent.
Because the theoretical yield is defined as the quantity of product produced when the limiting reagent reacts fully, the limiting reagent must be determined in order to compute the percentage yield of a reaction.