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Converting J/kg to kJ/mol 
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#1
Aug1811, 06:33 AM

P: 22

Let's say I have a value of:
553 x 10^5 j/kg How would I convert that to kJ/mol? 


#2
Aug1811, 07:14 AM

HW Helper
P: 4,435

mol = mass/molecular weight. = kg/M
kJ = 10^3 J 


#3
Aug1811, 07:17 AM

P: 22

so that means if I had 55300000 j/kg, that would be 55300 kJ/kg.
How would I make it into kJ/mol.... (sorry, i'm not very good at converting...) 


#4
Aug1811, 07:18 AM

P: 202

Converting J/kg to kJ/mol
from J to kJ all you need to do is of course to devide in 1000 (=k).
It's simply to look at it like this: 10^3j = kj => j = 10^3kj so 553 * 10^5 j = 553 * 10^5 * 10^3 kj = 553 * 10 ^2 kj (I substituted j for kj using the upper formula). About kg=>mol, well, for that you'll have to tell us what's the material involved. Imagine there are plastic and metal balls. A plastic ball weighs 1 kg and a metal ball 2kg. It'd be like asking you "how many balls are in a sack weighing 10kg?". If you knew it's plastic balls, you'd say 10. If it were metal balls, you'd say 5. so 1kg can be 1000 mol and it can be 1 mol => we need more information. 


#5
Aug1811, 07:19 AM

P: 22




#6
Aug1811, 07:23 AM

P: 202

Then use the relation given by rl.bhat and derive the connection between kg and mol. When you say 120, make sure if it's 120 g/mol or 120 kg/mol, and convert fittingly.



#7
Aug1811, 07:27 AM

P: 22

Assuming that my Molecular weight is 120g/mol..... Yeah, I have no idea. It seems like there's a missing variable to me :S 


#8
Aug1811, 07:34 AM

P: 202

How come?
rl.baht wrote: mol = mass / molecular weight. we want to know the connection between kg and mol. So assume you have 1kg material. Step 1: convert your molecular weight from 120g/mol => X kg/mol (you do it :) Step 2: use rl.baht connection written above, instead of mass you have "kg", and instead of molecular weight you have what you've calculated on Step 1. Step 3: from the formula of Step 2 isolate kg. You'll get something like kg = Y mol. Step 4: substitute kg for mol in the expression you've got. Give it a try, it's important and basic. If you won't make it I'll show you the way. 


#9
Aug1811, 07:44 AM

P: 22

Step Two: mol = mass/molecular weight = kg/0.12 = mol kg = 0.12mol So 55300kJ/0.12mol = 460833 kJ/mol Wow, that's a big number, did I do it right? 


#10
Aug1811, 07:47 AM

P: 202

hehe, the distance between the earth and the sun in centimeters is also a big number and it's still true :)
About the numbers  I really don't know about the 120 g/kg, you should make sure of that, but it seems you did it perfectly, great! 


#11
Aug1811, 07:49 AM

P: 22

Haha, thanks! :)



#12
Aug1911, 04:10 AM

HW Helper
P: 4,435

How much energy is produced by 0.120 kg? That is required energy per mol. 


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