# Why the mass of steam formed during condensation is equal to 9H2

1. Feb 15, 2013

### Elz

1. Why the mass of steam formed during condensation is equal to 9H2

While studying about the lower calorific value of fuel the equation is
L.C.V.= H.C.V. – heat of steam formed during combustion

Now here in the book they have written that,
Let ms = mass of steam formed in per kg of fuel = 9H2

Since the amount of heat per kg of steam is the latent heat of vaporization of water
corresponding to standard temperature of 15°C, is 2466 kJ/kg,

∴ L.C.V. = H.C.V.- ms X 2466 kJ/kg
= H.C.V. - 9H2 X 2466 kJ/kg …(∵ ms = 9H2)

What i don't understand is why this ms is equal to 9H2? what is the chemical reaction here? Why this value is considered constant for all fuels? can anyone please explain?

2. Feb 15, 2013

### Simon Bridge

3. Feb 15, 2013

### Elz

So 1 kg of H2 is equivalent to 9 kg of water or steam. So if our fuel has 5 kg H2 then 5X9 kg of steam will be formed. And if we condense it we will get this massX latent heat of vaporization of water=heat of steam formed during condensation.
Did I get it right?

4. Feb 15, 2013

### Simon Bridge

That's what I read - yep.

Careful - the ratio is approximate. It assumes all the hydrogen in the fuel gets used to make water - i.e. a very clean burn. The steam is at the boiling point. Stuff like that.
Good enough for a back-of-envelope calculation.

5. Feb 15, 2013

### Elz

Thanks for the help.. :)

6. Feb 15, 2013

No worries.