## Calculate the amount of substance

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chemistry028
Newbie Posts: 2
Joined: Sun Oct 03, 2021 5:49 am

### Calculate the amount of substance

P4+5O2→2P2O5.
I need to calculate what is the amount of 2P2O5 (and it is 4 mol)
The task says that there are 2mol of P4, so that means that i need 10mol of O2 for the reaction to happen, but how exactly do i predict that the amount of P2O5 is 4mol? What is the logic behind it?
ChenBeier
Distinguished Member Posts: 903
Joined: Wed Sep 27, 2017 7:25 am
Location: Berlin, Germany

### Re: Calculate the amount of substance

It's a given number. It can also 10, 0,5 98,67 mol or others
chemistry028
Newbie Posts: 2
Joined: Sun Oct 03, 2021 5:49 am

### Re: Calculate the amount of substance

No, the problem answer says this:

Knowing the amount of white phosphorus, the amount of phosphorus (V) oxide obtained is calculated according to the equation!
n P2O5=2*nP4=2⋅2mol=4mol , but i don't understand the logic behind this. This time the given number is that the white phosphorus is 2mol.
ChenBeier
Distinguished Member Posts: 903
Joined: Wed Sep 27, 2017 7:25 am
Location: Berlin, Germany

### Re: Calculate the amount of substance

Ok, it's a different question. Phosphorouspentoxide is existing bimolecular what means the real formula is P4O10.

The reaction is P4 + 5 O2 => P4O10 = 2 P2O5

But 4 mol is wrong, make no sense.