Question

When 3.5 mol Al react with 12.5 mol HCl, what is the limiting reactant and how many moles of H2 can be formed?

2 Al + 6 HCl 2 AlCl3 + 3 H2

HCl is the limiting reactant, 6.3 mol H2 can be formed

HCl is the limiting reactant, 3.2 mol H2 can be formed

Al is the limiting reactant, 3.5 mol H2 can be formed

Al is the limiting reactant, 5.3 mol H2 can be formed

Answer 1

@Festinger

Answer 2

Have you found the amount of mols of each reactant?

Answer 3

Oh right it's given. Compare the ratios.

Answer 4

\[amount\:Al\:needed\:if\:HCl\:is\:added:in\:excess=(\frac{mol\:of\:Al}{mol\:of\:HCl})*mols\:of\:HCl\]

\[amount\:HCl\:needed\:if\:Al\:is\:added:in\:excess=(\frac{mol\:of\:HCl}{mol\:of\:Al})*mols\:of\:Al\]

Answer 5

So if I had Al in excess, the calculation would look like:
\[\frac{6}{2}*3.5=10.5mols\:of\:HCl\]
In other words, 10.5mols of HCl reacts with 3.5mols of Al.

Answer 6

How many mols of Al are needed to react with 12.5mols of HCl?

Answer 7

ok hold i going to work it out

Answer 8

do i have to use the first formula you provide me to solve the question : How many mols of Al are needed to react with 12.5mols of HCl?

Answer 9

Yeap

Answer 10

\[\frac{ 3 }{ 12.5 }time12.5\]

Answer 11

i am stuck

Answer 12

nope, the term in brackets is the ratio from the balanced equation

Answer 13

oh so i used the wrong formula

Answer 14

\[\frac{ 6 }{ 2 }\times variable =12.5\]

Answer 15

\[\frac{2}{6}\times 12.5=\frac{25}{6}\]

Answer 16

What need need to do is to compare ratios... 6 mols of HCl reacts with 2 mols of Al, so how much Al will be reacted with 12.5mols of HCl?

Answer 17

i set up a proportion so i got 4.17

Answer 18

Yes

Answer 19

:) is that it?

Answer 20

So do you have enough Al to react with all 12.5 mols of HCl?

Answer 21

yes

Answer 22

You only have 3.5 mols of Al, but 12.5 mols of HCl needs 4.16 mols of Al to react fully.

Answer 23

what does it mean when it says limited reactant?

Answer 24

It means the reactant that does not have enough (in mols) to react fully

Let's say an reaction is \[A+B\rightarrow C\]

And I have 27 mols of A, and 5 mols of B.
The ratio of A to B is 1:1
Therefore for the reaction to complete fully, 27 mols of A must react with 27 mols of B, while for B we need 5 mols of B to react with 5 mols of A.

here, we see that B does not have enough to react with all of A, and we call B the limiting reagent.

Answer 25

In my example, when the reaction completes, I will have
22 mols of A (left over), 0 mols of B and 5 mols of C.

Answer 26

so it Al the limiting reagent?

Answer 27

Yes

Answer 28

Now you have to find how much H2 gas is produced from 3.5mols of Al!

Answer 29

what formula should i use?

Answer 30

It's similar to the ones we've used before, you just need to modify it abit. Give it a try.

Answer 31

5.3

Answer 32

Yes, 5.25 mols of H2 gas are produced. You got it!

Answer 33

yay thank you very much for all you help!