Homework Help: Chemistry

Posted by a Canadian on Thursday, February 21, 2013 at 5:16pm.

I had a quiz today and one of the multiple choice questions was something like, "find the final temperature of aluminum when it is cooled" and then it gave you the specific heat capacity of aluminum, the mass of the aluminum, initial temperature, and enthalpy change.

One of the options was that there was insufficient information because you need the mass of H2O used to cool the aluminum.

I chose that one... Is that right?

I chose it because I remember my teacher explaining that when you have a solid and a solution reacting, you only use the mass of the solution when doing Q=mc(detlaT). She said, "to explain it simply... What are you putting the thermometer in? The solid or the solution? You're not going to stick a thermometer into a solid." So I thought you'd need the mass of H2O because you can't use the mass of Al... But I overheard other people talking about it and I think a bunch of people calculated an actual value...

I just want to know if I got it right or wrong; it's been bugging me all day.

Chemistry - DrBob222, Thursday, February 21, 2013 at 5:31pm
"Something like" isn't enough for me to know.
q = mass Al x specific heat Al x (Tfinal-Tinitial)

If you used H2O to cool the Al you would need the mas of the H2O and the initial T of the H2O, then you could do the final T. Of course the final T of the water will be the same as the final T of the Al.
Chemistry - bobpursley, Thursday, February 21, 2013 at 5:31pm
enthlapy = heat change.

enthalpy change=mass*specheat*deltaTemp
Chemistry - a Canadian, Thursday, February 21, 2013 at 5:41pm
Thanks; I obviously got it wrong, but what was my teacher talking about when she said that when you have a solid reacting, you don't use the mass of the solid for Q=mc(deltaT), only the mass of liquids or solutions? Why wouldn't that apply in this case?

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