Need some help w/ a Calorimetry prob.

[WorkOnIt]

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Here it is:

CaCl2(s) -----> Ca(aq) + 2Cl(aq) Delta H= -81.5 k/J

An 11.0-g sample of CaCl2 is dissolved in 125 g of water, w/ both the substances at 25.0 . Calculate the final tempture of the solution assuming no heat lost to the surroundings and assuming the solution has a specific heat capacity of 4.18 J/C grams

if u know, please help.

P.S. the ans. is 39.2 C but try to explain how u get that ans.

Steve

 

[WorkOnIt]

bump

 

[SubSpring]

e=m*C*(temp change) if im not mistaken, hold on, lemme copy and paste this and check it out, eheh

ahh foget it

81.5=mass * heat cap *temp change

81.5 = 136 * 4.18 *(x-25)

x= final temp

temp change = final temp - begin temp (25)

 

[Ramoray]

i aint getting 39.. how do u do this one? im confused now

 

[SubSpring]

mass times heat capacity times the change in temp

so 125 g plus 11 g = 136 g

h/c of solution = 4.18

and the temp change is 39.2-25 = 14.2

136 * 4.18 * 14.2 = 8072.416 ( - 80.7 K/j cuz its exothermic)

 

[Ramoray]

damn briging back bad mcat memories, i forgot to convet the 80 into 8000! ahhhhh what is that convert? 80k/j? to 8000? what is that measured in.. i forget? ahh soo long ago!

 

[SubSpring]

e = 8000 joules, which is 8 kj

hmm .. maybe u meant -8 kj? cuz 80 kj = 80000 joules

 

[WorkOnIt]

Originally posted by SubSpring
e=m*C*(temp change) if im not mistaken, hold on, lemme copy and paste this and check it out, eheh

ahh foget it

81.5=mass * heat cap *temp change

81.5 = 136 * 4.18 *(x-25)

x= final temp

temp change = final temp - begin temp (25)

hey subspring, I totally forgot some of the math could u go step by step in solving for X

 

[alphabeta53]

Originally posted by WorkOnIt
hey subspring, I totally forgot some of the math could u go step by step in solving for X

Either you are an idiot or an ambitious 5th grader. Seriously... you don't know the math? I am surprised you found your way onto the internet....

 

[SubSpring]

im gonna use my #'s cuz i dont think yours are right, hehe


8150=136 * 4.18 * delta T

8150=568.48 * delta T

diovide by 568.48


delta T = roughly 14.3

add delta to the beginning temp (25) and u get 39.3 .. close enuff for my chem class

 

[WorkOnIt]

hmthe heat of change is -81.5 kJ. what did u use to covert to 8150 and whats the units

 

[SubSpring]

ok, if its 81.5 kj, = 81500 J

81500=136*4.18* delta T

81500=568.48 * delta T

divide by 568.48

delta T = 143.3

so your end. temp would be 168 C

sorry, thats just the way it is 😀

 

[Cerberus]

Originally posted by alphabeta53
Either you are an idiot or an ambitious 5th grader. Seriously... you don't know the math? I am surprised you found your way onto the internet....

there is no need to be a prick😡

 

[Cerberus]

ok, here we go

first find out how many moles you have of CaCl2

1 mole CaCl2=110.978g
11g/110.978=.09911

Now multiply this times the total energy created when one mole of CaCl2 dissociates.

.09911*81.5*1000=8078 (the 1000 is to convert from KJ to J)

now set up a simple equation

remember

q=SH*M*Delta T

therefor

8078=4.184*(125+11)*(t-25)

solve for t and you get 39.1965 C

 

[lola]

look at you go, cerberus!
givin helpful advice in pre-allo

 

[Cerberus]

Originally posted by lola
look at you go, cerberus!
givin helpful advice in pre-allo

heh, chem rocks

 

[WorkOnIt]

Thanks man!!

btw **** that anus alphabeta53

 

[SubSpring]

my help didn't count? 🙁

 

[heelshmeel]

Originally posted by Cerberus
8078=4.184*(125+11)*(t-25)

solve for t and you get 39.1965 C

yeeah, that's what I was thinking all along....😀

good job cerebrus

 

[Jacobim]

As Allen Iverson's Mom says, "Get out of here with that crazy stuff."