Chemical Forums

Chemistry Forums for Students => High School Chemistry Forum => Topic started by: hannah on April 20, 2006, 07:40:13 PM

Title: Heat transfer....
Post by: hannah on April 20, 2006, 07:40:13 PM

Uhh okay if you have different amounts of a solution and mix them how do you find the resulting temperature?

Specifically, if you have 30 g H2O at 40 degrees C and 100 g H2O at 70 degrees, what's the resulting temp??

Thanks...
hannah

Title: Re: Heat transfer....
Post by: Qazzian on April 20, 2006, 09:40:51 PM

For that, since it's the same type of liquid (water) in both, just take a weighted average of the temperatures.

Title: Re: Heat transfer....
Post by: mike on April 20, 2006, 10:12:56 PM

Thermometer ::)

Title: Re: Heat transfer....
Post by: hannah on April 20, 2006, 11:13:50 PM

I sort of thought of that, but what if its two different liquids like water and ethanol if i spelled that right?

Title: Re: Heat transfer....
Post by: Borek on April 21, 2006, 02:45:47 AM

Heat balance.

Title: Re: Heat transfer....
Post by: xiankai on April 21, 2006, 07:07:02 AM

heat loss by a substance = heat gain by another substance, assuming no heat loss to surroundings and 100% efficiency

the formula for heat is q = m c dT

where m is mass, c is the specific heat capacity and dT is the temperature change

Title: Re: Heat transfer....
Post by: hannah on April 21, 2006, 08:39:14 AM

Right but how do you do that with two unknowns? it doesn't give me Q or dT...

Title: Re: Heat transfer....
Post by: Borek on April 21, 2006, 08:59:43 AM

Q gained = Q lost, that takes care about first unknown.

Final temperature of both liquids is identical, that takes care of dT.

Title: Re: Heat transfer....
Post by: Donaldson Tan on April 21, 2006, 02:58:45 PM

Although there is 2 unknown (c and T_final), c cancels out because both "substances" are actually water and therefore have the same heat capacity.