Kaplan Thermochemistry Question Number 8

[bigmann4208]

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I was reading the explanation but I am still not getting the answer... Should delta T always be final minus initial? Why is it 100- x in the formula instead of x- 100?

Thanks for any help

 

[mug3n]

Can you type the question here? I don't think it's against board rules because it's not an official Pearson test, and a lot of people who post here doesn't have the Kaplan guide.

 

[bigmann4208]

Yeah the question is from the end of chapter review, not a practice test.
The question is:
A 50-g sample of metal was heated to 100 C and then dropped into a beaker containing 50 g of water at 25 C. If the specific heat capacity of the metal is 0.25 cal/g C, what is the final temperature of the water?

Thanks for the help

 

[ChippyChad]

I think it is:
50g (metal) x 0.25 x (100-Tfinal) = 50g (water) x 4.18 x (Tfinal-25)

i am too lazy to solve it 😛

 

[escse]

I think it is:
50g (metal) x 0.25 x (100-Tfinal) = 50g (water) x 4.18 x (Tfinal-25)

i am too lazy to solve it 😛

It looks right to me; if this is what was written on the Kaplan book, and bigmann4208 is wondering about this..


50g (metal) x 0.25 x (Tfinal-100) = delta T of metal
50g (water) x 4.18 x (Tfinal-25) = delta T of water

and delta T of water = - delta T of metal.

 

[bigmann4208]

I think it is:
50g (metal) x 0.25 x (100-Tfinal) = 50g (water) x 4.18 x (Tfinal-25)

i am too lazy to solve it 😛

Why is it (100-Tfinal) and not Tfinal - 100...I thought delta T is final minus initial?

 

[escse]

Why is it (100-Tfinal) and not Tfinal - 100...I thought delta T is final minus initial?

T final - 100 = delta T.
100 - T final = - delta T.

The reason why it is final miuns initial is because the delta T on the metal side is - delta T. The reason it is - delta T is because the change in temperature of metal is in the opposite direction of water; water had an increase in temperature, metal had a decrease in temperature.