# Homework Help: How in the bomb calorimeter the water is recondensed?

1. Feb 15, 2013

### Elz

1. In the bomb calorimeter used for the test the water is recondensed after it is vaporized

In the bomb calorimeter we measure the HHV as the steam formed there is condensed. What I want to know is how the steam is re condensed? In the wikipedia it says In more recent calorimeter designs, the whole bomb, pressurized with excess pure oxygen (typically at 30atm) and containing a weighed mass of a sample (typically 1-1.5 g) and a small fixed amount of water (to saturate the internal atmosphere, thus ensuring that all water produced is liquid, and removing the need to include enthalpy of vaporization in calculations), is submerged under a known volume of water
...
http://en.wikipedia.org/wiki/Calorimeter#Bomb_calorimeters

If a small amount of water is admitted into the bomb then how it is condensing the steam? Also Bomb calorimeter is called a constant volume calorimeter, What does this constant volume mean? As the bomb calorimeter has to withstand high pressure so what does this constant volume refer to?

2. Feb 15, 2013

### Staff: Mentor

Any additional steam would increase the humidity above 100%, therefore it condenses (unless the temperature increases significantly).
What is unclear about constant volume? The whole setup has a fixed volume, it cannot expand or emit any stuff.
That is a side-effect of the constant volume: The pressure can be high.

3. Feb 15, 2013

### Elz

I also found in a report that introducing pure oxygen to the bomb would increase the pressure in an isochoric chamber, thus ensuring that the water would be liquid. Can you please explain how it works? I mean i just want to be clear about the mechanism.

Why it is done in constant volume?

Thanks for you response.

4. Feb 16, 2013

### Staff: Mentor

A high pressure increases the boiling point.
The scientist wanted to study something at constant volume, I think. Why? That depends on the experiment.

5. Feb 16, 2013

### SteamKing

Staff Emeritus
Well, it is a bomb calorimeter.

If the reaction didn't occur at constant volume, that would imply that the bomb spread itself all over the lab.