If 37.4 grams of water decomposes at 297 Kelvin and 1.30 atmospheres, how many liters of oxygen gas can be produced? Show all of the work used to solve this problem.

2 H2O (l) yields 2 H2 (g) + O2 (g)

Question

If 37.4 grams of water decomposes at 297 Kelvin and 1.30 atmospheres, how many liters of oxygen gas can be produced? Show all of the work used to solve this problem. 

2 H2O (l) yields 2 H2 (g) + O2 (g)

somy · Answer

use PV=nRT

somy · Answer

$$PV = \frac{ mass }{ Mr }\times RT$$

rishavraj · Answer

18.69

somy · Answer

$$PV \times Mr = mass \times RT$$
make volume as a subject 
$$V =\frac{ mass \times RT }{ P \times Mr }$$

somy · Answer

Mr value of O2 gas u can find from periodic table. Covert unit of pressure to Pascals 
then substitute all the values to the final formula
your answer will be in m3 so convert it to dm3 (which is Liters) by multiplying it to 1000

somy · Answer

@rishavraj please do not give answers. It's against OS rules.

anonymous · Answer

Would I be using the mole ratio?

somy · Answer

no you don't need to, since they gave you mass)

rishavraj · Answer

okay

somy · Answer

by the way u r given Mass of water, so do make sure to find mass of O2 first

somy · Answer

and yes in that that case use mole ratio @yesy7

anonymous · Answer

I'm really confused. Okay so I use PV = nRT?

somy · Answer

sorry i didn't read that the mass was for water
forget what i said earlier :)
i'll take u step by step
first start with finding mole of water

anonymous · Answer

Okay. Can you help me with that?

somy · Answer

2 H2O (l) yields 2 H2 (g) + O2 (g)
you are given a mass of water 
so find mole of it 
$$mole =\frac{ mass }{ Mr }$$

somy · Answer

u can find Mr right?

anonymous · Answer

I know R but yeah I'm confused.

somy · Answer

Mr is molecular mass 
 forget about R for now :D

somy · Answer

Mr of H2O is = 2 H atoms= 2
                            1 O atom= 16

somy · Answer

16+2=18 and since coefficient of H2O in the reaction is 2 then multiply 18 by 2 and this will be your total Mr

somy · Answer

do u get it so far?

anonymous · Answer

Oh, I remember that now.

anonymous · Answer

So Mr is 36?

somy · Answer

:) good 
yeah)

somy · Answer

so now find the mole

anonymous · Answer

To find the mole I'm dividing 37.4 by 36, right?

somy · Answer

yes)

anonymous · Answer

So it would 1 or 1.04

somy · Answer

1.04 is right ) don't round of too much

somy · Answer

okay so now if you look at ratio between H2O and O2 
what can u say?

anonymous · Answer

is it 2:1

somy · Answer

good so what will be O2's mole then?

somy · Answer

if 2- 1.04
   1- ?

anonymous · Answer

.5?

somy · Answer

always take 3 significant figures in your answer to be on the safest side

somy · Answer

0.52 mole

anonymous · Answer

Okay.

somy · Answer

so now we have mole of oxygen gas

somy · Answer

now we can use PV=nRT

somy · Answer

P is ur pressure 
V is volume 
n is mole
R is constant = 8.31
T is temperature

anonymous · Answer

Which mole would I use?

somy · Answer

first
convert pressure to pascals

somy · Answer

the question is asking u for volume of oxygen so what do u think which mole u have to use?

anonymous · Answer

So would it be PV = (0.54)(0.0821)(297)

somy · Answer

mole is 0.52 
use 8.31 as your constant

somy · Answer

because i'm not really familiar with this one, so we can make mistake with units

anonymous · Answer

sorry typo okay

so '

PV = (0.52)(8.31)(297)?
Do I just multiply

somy · Answer

yes

somy · Answer

afterwards divide the value u get by pressure 
do make sure to convert atm to Pa

somy · Answer

1 atm is 101 325 pascals
1.30  atm is ?

anonymous · Answer

1283.3 / 131.69 = 0.97

anonymous · Answer

?

somy · Answer

1283.4/ 131722.5 =

anonymous · Answer

0.0097

somy · Answer

then straightaway multiply the answer by 1000 so that u get the answer in dm3

somy · Answer

when u do it in calculator, do the division, and do not erase it and straightaway multiply by 1000

anonymous · Answer

so it's 0.9743

somy · Answer

im getting 9.74 after rounding of

somy · Answer

in these type of calculations i would suggest you to round of ONLY final answer, so do not round of while you are doing same calculation (meaning u are working in same formula)

anonymous · Answer

I got the same thing the first time when I did 1283.3/131.69

somy · Answer

oh that's because u took pascals like that :)

anonymous · Answer

Oh, that's what I had in my notes so yeah.

somy · Answer

it's very important to consider units in all calculations thats why i use Pa and u used kPa :)

anonymous · Answer

I understand.

somy · Answer

but again if you used kPa make sure your unit of final product matches :)

somy · Answer

so do u get everything?

anonymous · Answer

Yeah, it's much clearer now. Thank you for your help!

somy · Answer

you are welcome :) if you have any doubts feel free to ask :) since i messed up ur brain in the beginning by reading the question wrong lol

anonymous · Answer

It's fine. I'm doing some more problems so I might have you double check them for me later. :)

somy · Answer

no problem :)