Question

Zinc and Hydrochloric Acid react according to the reaction $ Z{n_{(s)}} + HC{l_{(aq)}} \to ZnC{l_2}_{\left( {aq} \right)} + {H_2}_{(g)} \uparrow $ . If $ 0.40 $ mol $ Zn $ are added to hydrochloric acid containing $ 0.62 $ mol $ HCl $ . How many moles of $ {H_2} $ are produced?

Answer 1

Hint: Balance the given equation first. Apply the law of conservation - “The mass in an isolated system can neither be created nor be destroyed but can be transformed from one form to another”. According to the law of conservation of mass, the mass of the reactants must be equal to the mass of the products for a low energy thermodynamic process.

Complete answer:
Balance the given equation,
 $ Z{n_{(s)}} + 2HC{l_{(aq)}} \to ZnC{l_2}_{\left( {aq} \right)} + {H_2}_{(g)} \uparrow $
Balanced chemical reactions are balanced in terms of moles.
From the given equation,
 $ 2 $ moles of $ HCl $ reacts with $ 1 $ mole of $ Zn $ to produce $ 1 $ mole of $ {H_2} $
 $ 1 $ moles of $ HCl $ reacts with $ 0.5 $ moles of $ Zn $ to produce $ 0.5 $ moles of $ {H_2} $
 $ 0.62 $ moles of $ HCl $ reacts with $ (0.5 \times 0.62) $ moles of $ Zn $ to produce $ (0.5 \times 0.62) $ moles of $ {H_2} $
 $ 0.62 $ moles of $ HCl $ reacts with $ 0.31 $ moles of $ Zn $ to produce $ 0.31 $ moles of $ {H_2} $
Only $ 0.31 $ moles of $ Zn $ is used and $ 0.09 $ moles of $ Zn $ remains unreacted.
When $ 0.40 $ mol $ Zn $ are added to hydrochloric acid containing $ 0.62 $ mol $ HCl $ $ 0.31 $ moles of $ {H_2} $ are produced.

Note:
The molar mass of a substance, in grams, is numerically equal to one atom or molecule's mass in atomic mass units. A balanced chemical reaction gives equivalences in moles that allow stoichiometry calculations to be performed.
Mole quantities of one substance can be related to mass quantities using a balanced chemical equation. Mass quantities of one substance can be related to mass quantities using a balanced chemical equation. In all cases, quantities of a substance must be converted to moles before the balanced chemical equation can be used to convert to moles of another substance.