Question

Help Please!!

A block of brass of mass 500 gram and temperature 100C is placed in 300 grams of water at 20C which is in an aluminium calometer of mass 75 grams. If the final temperature is 30C calculate the specific heat of brass?

Cwater = 4200J/kg/C
Calum= 880J/kg/C

Answer 1

From newton's heat transfer we know that mCpdT=constant for all three bodies. This basically says that q=constant through the system. So what type of equation can you set up after knowing this?

Answer 2

where m=mass, Cp=specific heat, and dT=temp change

Answer 3

heat loss from brass = heat gained by aluminium + heat gained by water

Answer 4

i was trying mCdT of brass = mCdT of alimunium + mCdT of water 9 but maybe i should have subtracted)

Answer 5

Very good young sir

Answer 6

omit 9

Answer 7

haha neither young nor a sir but thanks :D young man

Answer 8

for the final temp of the Brass do I use the 20C or the 30C ?

Answer 9

It says the final bulk temp of brass is 30. Use 30 for brass. The 20 is for the water

Answer 10

Also make sure to use kg not grams. Bc the Cp values are in a kg basis

Answer 11

so dont use 500 grams or 300 grams use .5kg or .3kg

Answer 12

ok so for the Brass .5 * C * (30-100)

Answer 13

water is .3 * 4200 * (30-20)

Answer 14

and Aluminium is .075 * 880 * (30-20)

Answer 15

im lost here... I am not getting 3770 which is the C of brass

Answer 16

Yep and I got about 378J/kgK which is very close to the listed value of about 380 J/kgK

Answer 17

Not sure where you get 3770? A good reference is here http://www.engineeringtoolbox.com/specific-heat-metal-alloys-d_153.html which lists about 380

Answer 18

my book has a list... hmm ok ill check it out

Answer 19

my book lists it as J/kg/C

Answer 20

but im confused as I used 4200 and 880 which is J/kg/C why don't i get the 3770 j/kg/C :S

Answer 21

Has to be a typo. That value does not even make sense. The heat capacities of solid metals are usually low, under 500 J/kgK

Answer 22

specific heats* not capacities

Answer 23

The method we did is correct. You get a negative value at the end because the brass is losing heat, so q is negative.

Answer 24

ok so i write it as J/kg/K ? i'll attach the table shown in my book

Answer 25

that's why i was expecting the 3770 lol i don't think i fully understand this topic yet.

Answer 26

Bro i would not get too worked up about it. We did the math, and our answer is about 380. All other references show 380. http://www.diracdelta.co.uk/science/source/s/p/specific%20heat%20capacity/source.html#.UoLdLeL-Upc

Answer 27

Yet another trusted referenc ehsowing 370 J/kgK

Answer 28

alrighty thanks so much for your help i trust a chem engineer hahah

Answer 29

Indeed you should, as i spent an entire year studying heat transfer! Anytime man...

Answer 30

cheers braaaaah