[Isomer]

Hi....I've been working at this one for over an hour and am stumped....

A 90.00g piece of aluminium is placed on top of a 120.00 g piece of copper which has a higher initial temp than the aluminium. The copper loses 7.21 kJ of energy to the aluminium (assume no loss of energy to the surroundings). The copper has a final temp of 47.3 degrees celsius when thermal equilibrium is reached. What is the initial temp of both metals??

This is what I have done so far...

aluminium.....m=90, c=.897, final temp=47.3
copper.....m=120, c=.385, final temp=47.3

Here are my equations so far....

1. mc(delta temp) aluminium = mc(delta temp) copper

2. mc(final temp - initial temp) aluminium = mc( initial temp - final temp) copper

3. mc(final temp) aluminium + mc(initial temp) aluminium = mc(initial temp) copper + mc(final temp) copper

4.mc(final temp) al + mc(final temp) cu = mc(initial temp)cu + mc(initial temp)al

5. 6003.789 = mc(initial temp) cu + mc(initial temp) al

I need to find the initial temp of each metal....but I'm at a standstill. I tried factoring out the initial temp but that doesn't work because it gives me the same answers for both initial temps. Any ideas where to go from here? Or did I screw up earlier???

[sdekivit]

2. mc(final temp - initial temp) aluminium = mc( initial temp - final temp) copper


3. mc(final temp) aluminium + mc(initial temp) aluminium = mc(initial temp) copper + mc(final temp) copper

think again: is this mathematically correct ? You'll probably know: ab(c-d) = abc - abd

But besides of this:

of copper which has a higher initial temp than the aluminium. The copper loses 7.21 kJ of energy to the aluminium (assume no loss of energy to the surroundings).

since the initial temperatures aren't the same, you can't use this approach. You can use this equation to calculate the final temperature since that has the same value. That's why you come at an answer of 47,3 C, because 0 = 0.

The question already says the copper losses 7,21 kJ to the aluminum, so this is Q.

--> - Q = c * m ( 47,3 - T) = c * m * (T - 47,3)

[Isomer]

Sorry....you are right...I typed it out wrong. But even if I make that correction I still don't know how to isolate each initial temperature!!!

[sdekivit]

Sorry....you are right...I typed it out wrong. But even if I make that correction I still don't know how to isolate each initial temperature!!!

see my first reply, i was busy editing it 

[Isomer]

Thanks for the reply. Much appreciated.