Question

Ok, I really need help with this one:

In a particular reaction, 53.8 g of liquid silicon tetrachloride is added to 65.0 g of solid magnesium to produce solid magnesium chloride and solid silicon. What is the excess reagent for the forward reaction?
MgCl2
Mg
Si
SiCl4

Answer 1

First you have to convert to moles. This is a lengthy problem so pull out your calculator. So you find the moles of each reactant. Those are the moles that you physically have.
After you are going to find how much you need for each one, so:
Find the mole ratios between the reactants (look at the coefficients) , for this you need the equation of the reaction

Answer 2

How do you find the moles of the other ones not given grams?

Answer 3

after you find the ratios. what is the equation?

Answer 4

Oh..... So, I got .5169 for silicon tetrachloride and 2.674 for magnesium. Where do I go from there?

Answer 5

good, now what are the ratios of the between the reactants?

Answer 6

Wait, how do I get that?

Answer 7

from the equation of the reaction

Answer 8

So... .5169 divided by 2.674?

Answer 9

did they give you an equation for this reaction?

Answer 10

Nope.

Answer 11

It says "In a particular reaction"

Answer 12

ok, so based on what they give you have to balance the equation now we have:
\[SiCl _{4}+2Mg \rightarrow 2MgCl _{2}+Si\]

Answer 13

this is the balanced equation

Answer 14

So, it's a 2/1 ratio?

Answer 15

correct

Answer 16

So I divide .5169 by 2?

Answer 17

what moles are the .5169?

Answer 18

Silicon Tetrachloride

Answer 19

so .5169 times 2

Answer 20

gives you moles of Mg

Answer 21

So, 1.0338

Answer 22

yep. now divide 2.674 by 2 thats moles of SiCl4

Answer 23

So 1.337

Answer 24

yup. now make sure you label so you dont get confused , the moles that we calculated now is the moles that we need for the reaction to happen. we are gonna compare these to the moles that we had (what we did in the begining)

Answer 25

just write down the moles that we have and the moles we need correctly labeled so we can find the excess.

Answer 26

The moles we have:

1.0338 Silicon Tetrachloride
1.337 Magnesium

Answer 27

The moles before we divided and multiplied were .5169 and 2.674

Answer 28

.5169 Silicon Tetrachloride
2.674 Magnesium

Answer 29

ok the .51.. and 2.67 is what we have . the 1.03 and 1.333 is what we need.

Answer 30

SiCl4 is the limiting reactant and Mg is the excess

Answer 31

Ok! Thanks so much!

Answer 32

no problem!