Register to reply

Calculating Final Temperature

by TrueStar
Tags: final, temperature
Share this thread:
Nov18-09, 05:44 PM
P: 93
1. The problem statement, all variables and given/known data

A piece of iron weighed at 120 grams at 95.0 degrees Celcius is added to 750ml water of 25.0 degrees Celcius. What is the final temperature of the water when it is equilibrated? Assume the dentisy of water is 1 g/ml. (Specific heat of water is 4.184 and specific heat of iron is .449).

2. Relevant equations

q=mc(delta t). In this case the q of iron is equal to the q of water.

3. The attempt at a solution

Here is my setup:



I know this is wrong, but I'm not sure if it's because I set this up wrong or did my calculations incorrectly.
Phys.Org News Partner Science news on
Experts defend operational earthquake forecasting, counter critiques
EU urged to convert TV frequencies to mobile broadband
Sierra Nevada freshwater runoff could drop 26 percent by 2100
Nov18-09, 05:54 PM
Sci Advisor
HW Helper
P: 8,953
It's a sign error, the change in temperature from 95>x and 25->x must be different signs
Nov18-09, 06:08 PM
P: 93
I don't understand what you mean. I know that 23.85 implies that the temperature decreased for both the iron and water, and that is wrong.

Nov19-09, 03:12 AM
Borek's Avatar
P: 23,599
Calculating Final Temperature

mgb points out that there is a sign error in your original equation.

Nov19-09, 06:06 PM
P: 93
I think I forgot the qin=-qout concept. Let me try again.


x=26.18 degrees Celcius

Is this what you were referring to?
Nov19-09, 06:13 PM
Sci Advisor
HW Helper
P: 8,953
if one thing is cooling from 95deg to x then the change in T is (95-x)
then if the other is heating form 25 to X the change must be (x-25) which gives the different signs.

Putting a minus on one side is the same thing (or at least has the same effect)
Nov19-09, 06:39 PM
P: 93
I thought that in order to do the equation correctly, one must always subtract the initial temperature from the final temperature.
Nov19-09, 07:54 PM
Sci Advisor
HW Helper
P: 8,953
The change in temperature defines the heat flow, so heat in and heat out would have different signs.
Nov19-09, 08:07 PM
P: 93
I see. Thank you for checking out my question and taking the time to explain it. :)

Register to reply

Related Discussions
What is final temperature? Introductory Physics Homework 8
Calculating Final Temperature Biology, Chemistry & Other Homework 5
Calorimetry- how do I know the final temperature? Biology, Chemistry & Other Homework 2
Final temperature of system Introductory Physics Homework 2
Final temperature Introductory Physics Homework 0