g'chem q

[dat_student]

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20 g of NaCl is poured into 250 ml of H2O. temp drops 1 C. what is the heat of solution?

 

[sgdorfl90]

20 g of NaCl is poured into 250 ml of H2O. temp drops 1 C. what is the heat of solution?

my best guess would be 1 cal, since that's what it takes to heat 1 degree, so reduction by that much releases 1 cal to the environment...thanks DAT student for making me question my studying...again.

 

[dat_student]

my best guess would be 1 cal, since that's what it takes to heat 1 degree, so reduction by that much releases 1 cal to the environment...thanks DAT student for making me question my studying...again.

you're very welcome but wrong answer 🙂

 

[sgdorfl90]

you're very welcome but wrong answer 🙂

wait...the environment was reduced by 1 degree...does that mean it gained 4.18J of energy...so heat of sol. should be +4.18J...let me know the right answer

 

[dat_student]

wait...the environment was reduced by 1 degree...does that mean it gained 4.18J of energy...so heat of sol. should be +4.18J...let me know the right answer

wrong again 🙂

 

[sgdorfl90]

wrong again 🙂

where do u get these questions??? please PM me the answer if u don't want others to see it...thanx

 

[dat_student]

where do u get these questions??? please PM me the answer if u don't want others to see it...thanx

3

 

[sgdorfl90]

3

if u don't mind...can u explain how u got the answer...i tried and failed...thanks for helping me out

 

[dat_student]

if u don't mind...can u explain how u got the answer...i tried and failed...thanks for helping me out

u tried for 5 min, so impatient

 

[sgdorfl90]

u tried for 5 min, so impatient

****'s not coming to me bro...i hit a dead-end, and I am just wasting time...can u please show me how the right answer is derived. Thanks.

 

[duh?]

Quit playing dat student, anyody knows that 5mins on a question like that is NOT GOOD (try spending 5 mins on each DAT question and tell me how you do). Could you tell us how to do it or are u going to be a pain? Besides what kinda answer is 3. Didn't ur teachers tell you to always put units with ur answers. 3! 3 what? cows? I'm just pulling ur legs but yeah, i'm getting frustrated too. 🙂

 

[dat_student]

Quit playing dat student, anyody knows that 5mins on a question like that is NOT GOOD (try spending 5 mins on each DAT question and tell me how you do). Could you tell us how to do it or are u going to be a pain? Besides what kinda answer is 3. Didn't ur teachers tell you to always put units with ur answers. 3! 3 what? cows? I'm just pulling ur legs but yeah, i'm getting frustrated too. 🙂

oop! sorry. 3 kj/mol

 

[sgdorfl90]

oop! sorry. 3 kj/mol

Duh...what Mr. DAT student did not give us is the enthalpy of hydration and Lattice enthalply for salt dissolved in water, which is 784KJ/mol, and 787KJ/mol respectively. Now you find the number of moles of NaCl, and then find the final Lattice enthalply and enthalpy of hydration. Lattice enthalply, btw is the solute-solute bond breaking, and enthalpy of hydration is solvent-solvent breaking + solute-solvent forming. The number of moles of NaCl for this is close to 1, so, we can just subtract enthalpy of lattice-that of hydration to land at a grand number of 3KJ/mol.


To😀AT student, I know u wanna give others a try, but if u do post a question, can u post a workout answers too, cuz many ppl will be fustrated and won't be able to do anything if they don't understand this one...at least it happens to me. Thanks

 

[dat_student]

...To😀AT student, I know u wanna give others a try, but if u do post a question, can u post a workout answers too, cuz many ppl will be fustrated and won't be able to do anything if they don't understand this one...at least it happens to me. Thanks

ADA won't tell you the correct answers for the real DAT. 🙂
SIDE NOTE: Some parts of your last argument are not true.

 

[duh?]

Can someone please say SHUT UP?! 🙄 Thanks a lot Mybaa. 😀 I'm sure dat student had no idea how to solve the problem. 🙄 😡

 

[dat_student]

Can someone please say SHUT UP?! 🙄 Thanks a lot Mybaa. 😀 I'm sure dat student had no idea how to solve the problem. 🙄 😡

I had no idea. Thanks for helping me find the answer.

 

[sgdorfl90]

yo bro...if u can help me out as to where my arguments r wrong, it would help in the future...keep up the good work, and just take that test and get a 30 man.

 

[howui3]

DAT STUDENT IS AN ASS! if you want to help people improve on the DAT try EXPLAINING ANSWERS! that will go a lot furhter then 3kj/mol!

 

[dat_student]

yo bro...if u can help me out as to where my arguments r wrong, it would help in the future...keep up the good work, and just take that test and get a 30 man.

no other info (lattice, enthalpy etc) was needed. simply divide the number by 1/3 mole of NaCl, 1 / (1/3) = 3 kj/mole

 

[Flipper405]

no other info (lattice, enthalpy etc) was needed. simply divide the number by 1/3 mole of NaCl, 1 / (1/3) = 3 kj/mole

Again, where did you get "the number" from? I assume that would have to be 1 kj, and I don't see that anywhere in the problem...

 

[dat_student]

Again, where did you get "the number" from? I assume that would have to be 1 kj, and I don't see that anywhere in the problem...

(m*c*delta temp) gives you "1"

 

[sgdorfl90]

(m*c*delta temp) gives you "1"

hey, I don't think doing m*c* change in T works as u want it to in this case...doing 4.18 * 250G * 1 degree change does give 1045 J, which is around 1 KJ, but the addition of salt does change the specific heat capacity, in which case this does not really work out the way u want it to. those r my 2 cents, let me know what u think.

 

[heshyn2000]

hey, I don't think doing m*c* change in T works as u want it to in this case...doing 4.18 * 250G * 1 degree change does give 1045 J, which is around 1 KJ, but the addition of salt does change the specific heat capacity, in which case this does not really work out the way u want it to. those r my 2 cents, let me know what u think.

I think, (i) wont change delta H it will only effect the coligitive properties.

 

[dat_student]

hey, I don't think doing m*c* change in T works as u want it to in this case...doing 4.18 * 250G * 1 degree change does give 1045 J, which is around 1 KJ, but the addition of salt does change the specific heat capacity, in which case this does not really work out the way u want it to. those r my 2 cents, let me know what u think.

NaCl was not added to a salt solution. We want to know the heat as a result of adding NaCl. Finding just the heat is meaningless. So you have to find "heat per mole."