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Calculation problems with Heat lost = Heat gained problem. PLEASE HELP
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Topic: Calculation problems with Heat lost = Heat gained problem. PLEASE HELP (Read 13388 times)
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babyrecept107
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Calculation problems with Heat lost = Heat gained problem. PLEASE HELP
«
on:
October 05, 2011, 02:40:40 PM »
I am having an issue with this problem.
A piece of gold with a mass of 45.5 g and a temperature of 80.5 C is dropped into 192 g of water at 15.0 C. What is the final temperature of the water?
I did the Q
1
= Q
2
equation:
M x C x (t
i
- t
f
) = M x C x (t
i
+ t
f
)
(45.5g)(0.129J/g C)(80.5 C - t
f
) = (192g)(4.18J/g C)(15.0 C + t
f
)
5.8695(80.5 C - t
f
) = 802.56(15.0 C + t
f
)
472.495 - 5.8695t
f
= 12038.4 + 802.56t
f
808.4295t
f
= 11565.905
t
f
= 14.31 C
That cannot be the right answer because the answer has to be between 15.0 and 80.5 .
PLEASE HELP because this question has been bothering me for a week.
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jusy1
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Re: Calculation problems with Heat lost = Heat gained problem. PLEASE HELP
«
Reply #1 on:
October 05, 2011, 03:30:52 PM »
Your equation should be:
M x C x (tf - ti) = - M x C x (tf - ti)
On the left side you put heat given away by the piece of gold and on the right side the heat absorbed by water:
M x C x (tf - 80.5) = - M x C x (tf - 15)
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babyrecept107
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Re: Calculation problems with Heat lost = Heat gained problem. PLEASE HELP
«
Reply #2 on:
October 05, 2011, 03:38:19 PM »
It gives me the same answer...
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DrCMS
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Re: Calculation problems with Heat lost = Heat gained problem. PLEASE HELP
«
Reply #3 on:
October 06, 2011, 04:57:13 AM »
The correct equation should be
M
Au
x C
Au
x (80.5-Tf) = M
H
2
0
x C
H
2
0
x (Tf - 15)
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babyrecept107
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Re: Calculation problems with Heat lost = Heat gained problem. PLEASE HELP
«
Reply #4 on:
October 06, 2011, 02:47:32 PM »
M x C x (80.5 - t
f
) = M x C x (t
f
- 15)
(45.5)(0.129)(80.5 - t
f
) = (192)(4.18)(t
f
- 15)
5.8695(80.5 - t
f
) = 802.56(t
f
- 15)
472.495 - 5.8695t
f
= 802.56t
f
- 12038.4
12510.895 = 808.4295t
f
15.48 C = t
f
I still don't think that's right. The temperature of the gold wouldn't dramatically drop like that... Would it?
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Dan
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Organic Chemist
Re: Calculation problems with Heat lost = Heat gained problem. PLEASE HELP
«
Reply #5 on:
October 06, 2011, 03:04:22 PM »
Sounds fine. Remember there is ~4 times as much water (by mass) as gold, and the heat capacity of water is ~30 times that of gold. You would expect the temperature of the gold to drop far more than the temperature of the water would rise.
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babyrecept107
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Re: Calculation problems with Heat lost = Heat gained problem. PLEASE HELP
«
Reply #6 on:
October 06, 2011, 03:09:10 PM »
Thank you very much.
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Calculation problems with Heat lost = Heat gained problem. PLEASE HELP