Thermal Energy

[allsirgarnet]

Although not strictly homework, the question I think is basic enough for this sub-forum if thats ok thanks, despite my complete ignorance of subject.

 

Set up.

 

A sealed/insulated volume of 25 cubic litres of air, at 1 atmosphere pressure, preheated to a temperature of roughly 2300C (two thousand three hundred).

 

Heres the question please.

 

If 3cc/mil room temperature fresh water is added to the volume of air, with the intention of converting the water to steam at presumably 2300C, once the conversion is completed by how much in centigrade with the overall temperature of the air/steam volume fall?

 

Put another way...

 

Given the setup, what will be the final overall temperature in centigrade of the volume of air/steam mix, once the water to steam conversion is completed.

 

 

I've had various answers ranging from a 10C overall drop in temperature upto 530C overall drop in temperature, but no one so far seems certain.

 

Can anyone please help me resolve this problem?

 

Very many thanks in advance.

 

Gary

[swansont]

You need to know the heat capacity of the air and water vapor, as well as the latent heat of vaporization of the water. You also need to specify the temperature of the water

 

http://en.wikipedia.org/wiki/Heat_capacity

http://en.wikipedia.org/wiki/Latent_heat

 

Water's latent heat of vaporization is 2260 J/g, so 3 grams means 6780 J, and air has a specific heat capacity of about 29 J/mol-K, and you have about a mole of air, so just flashing 3g of water to steam at 100ºC will drop the temperature by more than 230ºC.