Question

If 34.2 grams of lithium react with excess water, how many liters of hydrogen gas can be produced at 299 Kelvin and 1.21 atmospheres? Show all of the work used to solve this problem.

2 Li (s) + 2 H2O (l) yields 2 LiOH (aq) + H2 (g)

Answer 1

Number of Moles=Mass(g)/Molar Mass(g/mol)
34.2/6.94=4.927 Moles of lithium
Mole Ratio of Lithium to Hydrogen 2:1
2:1
4.927:x
xmole of hydrogen=4.927*1/2=2.463
Use ideal gas equation
PV=nrt
Pressure is measured in pascals
1 atmosphere = 101,325 Pa
1.21 atmosphere=122603.5Pa--->1.21*101325
Volume is measured in m^3
The SI value for R is 8.31441 J K-1 mol-1.
122603.5*V=8.31441*2.463*299
V=0.0499 m^3
1m^3--->1000litre
0.0499m^-->49.9litre--->0.0499*1000/1

Answer 2

im confused

Answer 3

about which part?

Answer 4

reading and understanding tha entire thing...

Answer 5

moles Li = 34.2 g / 6.941 g/mol=4.927
the ratio between Li and H2 is 2 : 1
moles H2 = 4.927/2 = 2.463
to obtain the volume of hydrogen gas we use the equation PV=nrt
P stands for pressure and is measured in pascal not in atmosphere thats why i changed the unit
V is measured in m^3 but in your question Volume has to be litres so i changed units by * by 1000
n is 2.463 moles
R is a gas constant 8.31441

Answer 6

You use Pv=nrt if you have a gas and you are given P, V or T data, and asked to find moles, or P or V or T or molar mass of the gas.

Answer 7

do u get it now? @ThaPaintballer
good job @Abmon98 !!

Answer 8

Thanks, @Somy :D

Answer 9

kind of, still a little lost tho with tha conversions..

Answer 10

well look
when we use PV= nRT
we need to use SI system units
which are
P= Pascal
V= m3
n= mole
R= 8.14 (this value is like this because of the units we are using --> http://www.csupomona.edu/~lllee/gasconstant.pdf )
T= Kelvin

Answer 11

is it clear now?
there is your way also
meaning no conversions

in that case it will be
P= atm
V= L
n= mole
R= 0.08206 (check out in the link i gave you-> you will see that unit will match the units im using here)
T= Kelvin

Answer 12

so you don't need to convert anything, u can just use it with your units
BUT of course you gotta know when which R value to use
depending on the units you are taking

if you are taking P as atm and V as L then your R will be = 0.08206

if you are taking P as Pascal and V as m3 then your R = 8.31

(btw sorry i its 8.31 not 8.14 )

Answer 13

does it make sense now?

Answer 14

yeah i'm kind of starting to piece it together, so 8.31 is tha answer?

Answer 15

no its R value - when u use V as m3 and P as Pa
then u put the values into the formula and get the unknown V

Answer 16

but since the question is asking for volume in Liters
i'd suggest not to convert anything

Answer 17

so in PV =nRT 8.31 is subsituted for V but how do i get tha other units?

Answer 18

leave pressure as atm and use R as 0.08206

Answer 19

nooo 8.31 is value of R!

Answer 20

we do not know V and we need to find it

Answer 21

we know P= 1.21atm and T= 299 Kelvin and R= 0.08206 and we also know mole of Hydrogen

Answer 22

we do not know Volume so we can find it using PV= nRT
make V as subject so ==> V= nRT/P

Answer 23

okay, so what is 'n' replaced with?

Answer 24

with mole

Answer 25

umm ok... so its v = mole*0.08206*299 / 1.21?

Answer 26

yes
you have mole

Answer 27

put mole also
or you don't get how you got mole??

Answer 28

yeah i didnt really understand when you said its mole. chem isnt exactly my subject haha

Answer 29

oop, never mind i get it now. so tha final answer is 50 L? @Somy

Answer 30

idk lol if you calculated the way i told you then yes :))

Answer 31

yeah lol i just checked :D

Answer 32

well done both of you @Abmon98 @ThaPaintballer :D

Answer 33

thanks haha (: so which one of you two do i give tha medal to? :3

Answer 34

him :) he did the whole job lol i didn't do much :)

Answer 35

alright, thanks again both of you! (:

Answer 36

:))

Answer 37

@Somy your good at teaching :) i think somy should receive a medal because she made it clear. thank you btw and its my pleasure @thapaintballer