# Converting J/kg to kJ/mol

by clintyip
Tags: converting, j or kg, kj or mol
 P: 22 Let's say I have a value of: 553 x 10^5 j/kg How would I convert that to kJ/mol?
 HW Helper P: 4,433 mol = mass/molecular weight. = kg/M kJ = 10^3 J
 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...)
 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.
P: 22
 Quote by Tomer 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 kg 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.
Well, this is actually a fuel, Kerosene, with a molecular weight of 120...
 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.
P: 22
 Quote by Tomer 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.
So I have 55300 kJ/kg

Assuming that my Molecular weight is 120g/mol.....

Yeah, I have no idea. It seems like there's a missing variable to me :S
 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.
P: 22
 Quote by Tomer 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.
Step One: 120g/mol => 0.12kg/mol
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?
 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!
 P: 22 Haha, thanks! :)
HW Helper
P: 4,433
 Quote by clintyip Step One: 120g/mol => 0.12kg/mol 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?
1 kg of kerosene produces 55300 kJ of energy.
How much energy is produced by 0.120 kg? That is required energy per mol.

 Related Discussions Electrical Engineering 3 Classical Physics 4 Introductory Physics Homework 2 Introductory Physics Homework 3 Introductory Physics Homework 4