Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: bluemidnight on March 07, 2006, 12:11:51 PM
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Hi it's my first time here.
Can someone please help me. I don't know how to answer the following question:
5g of iron at 75.0 degrees C is added to 150.0g of water at 15.0 degrees C in a calorimeter. What is the final temperature of the iron and water? (For iron, c=0.444J/g*degrees C, for water c=4.18J/g*degrees C)
I know the equation I have to use is q=m x c x delta T, I just don't know what to do. Any help will be very much appreciated :)
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So you already have one equation for the water and one for iron: q=m x c x delta T
The heat given off by the iron is the same amount of heat absorbed by the water, so set the q (heat) equal to each other.
m x c x delta T = m x c x delta T
(let's say the left side of the equation is for the iron and the right side is for the water)
the final temp. has to be the same for both
delta T = T_final - T_initial
let's call T_final: "y" (just as a variable)
delta T = y - T_inital
so now your equation is:
m x c x (y - T_inital) = m x c x (y - T_inital)
(remember the left side of the equation is for the iron and the right side is for the water)
now just plug in your numbers and solve for "y" because that was the variable chosen to represent final temperature.
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m x c x (y - T_inital) = m x c x (y - T_inital)
This is correct thinking, but incorrect use of symbols. Never use same symbol to denote two values. First because the equation you set up is incorrect from the formal point of view, second, because it is too easy to lost control over your calculations.
mH2O x cH2O x (Tfinal - TstartH2O) = mFe x cFe x (Tfinal - TstartFe)
Solve for Tfinal.
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sorry! I missed the subscript icon
I'll remember that from now on ;)
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Thank you so much! You were both very helpful. I really appreciate it