Converting J/kg to kJ/mol

  • Thread starter clintyip
  • Start date
In summary, to convert 553 x 10^5 j/kg to kJ/mol, you need to first convert the molecular weight from 120g/mol to 0.12kg/mol. Then, use the formula mol = mass/molecular weight to find the relationship between kg and mol. Finally, substitute the value for mol into the expression to get the final conversion of 460833 kJ/mol.
  • #1
clintyip
22
0
Let's say I have a value of:

553 x 10^5 j/kg

How would I convert that to kJ/mol?
 
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  • #2
mol = mass/molecular weight. = kg/M
kJ = 10^3 J
 
  • #3
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
from J to kJ all you need to do is of course to divide 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
Tomer said:
from J to kJ all you need to do is of course to divide 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...
 
  • #6
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
Tomer said:
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
 
  • #8
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
Tomer said:
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?
 
  • #10
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
Haha, thanks! :)
 
  • #12
clintyip said:
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.
 

What is the formula for converting J/kg to kJ/mol?

The formula for converting J/kg to kJ/mol is to divide the value in J/kg by the molar mass of the substance in kg/mol.

Can you provide an example of converting J/kg to kJ/mol?

For example, to convert 100 J/kg to kJ/mol for a substance with a molar mass of 20 kg/mol, you would divide 100 by 20 to get 5 kJ/mol.

Why do we need to convert J/kg to kJ/mol?

Converting J/kg to kJ/mol allows us to compare the energy per mass of different substances. It also allows us to use the molar mass of the substance to calculate the energy per mole.

What is the difference between J/kg and kJ/mol?

J/kg is a unit of energy per mass, while kJ/mol is a unit of energy per mole. Converting between the two units accounts for the difference in the amount of substance.

Are there any other units for energy per mole besides kJ/mol?

Yes, there are other units for energy per mole, such as J/mol and kcal/mol. These units can also be converted to kJ/mol using conversion factors.

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