[monarchus]

When 5.00 J of heat are added to 1.50 g of cobalt, its temperature rises by 3.42 degree Celsius. What is the molar heat capacity o cobalt in J mol-1 K-1?

A) 0.710
B) 0.875
C) 2.30
D) 57.4


P.S. if your answer is A, please explain why you want to add 273 to the change of the temperature to make it Kelvin. Wasn't change of temperature is the same no matter it is in the form of degree Celsius or Kelvin?

thank you.

[DrCMS]

What do you think the answer is?

Show your work and we'll help you if you're wrong but we're not just going to give you the answer.

[monarchus]

What do you think the answer is?

Show your work and we'll help you if you're wrong but we're not just going to give you the answer.

okay

actually, i tried, and my answer wrong, asked my teacher, he insisted that A is the correct answer, just that i didn't show here

Q = n x c x T

Q = heat evolved
n = number of moles
c = molar heat capacity
T = change in temperature


5 = (1.5 / 58.9 ) x c x 3.42

c = 57.4

[sameeralord]

What do you think the answer is?

Show your work and we'll help you if you're wrong but we're not just going to give you the answer.

okay

actually, i tried, and my answer wrong, asked my teacher, he insisted that A is the correct answer, just that i didn't show here

Q = n x c x T

Q = heat evolved
n = number of moles
c = molar heat capacity
T = change in temperature


5 = (1.5 / 58.9 ) x c x 3.42

c = 57.4

Hello. I haven't learned these stuff at school yet but looking at the formulas and stuff I think you should add 273. The question asks for it
J mol-1 K-1. What you have done is J mol-1 C-1.

[Dan]

Hello. I haven't learned these stuff at school yet but looking at the formulas and stuff I think you should add 273. The question asks for it
J mol-1 K-1. What you have done is J mol-1 C-1.

A temperature change in K is exactly the same as a temperature change in C, there is no need to add 273 to anything.

[Borek]

Let's assume T_start = 100 ºC, T_final = 105 ºC.

Delta T = T_final - T_start = 105 ºC - 100 ºC = 5 ºC

Now in Kelvins: T_start = 100 + 273 = 373 K, T_final = 105 + 273 = 378 K.

Delta T = T_final - T_start = 378 K - 373 K = 5 K

No matter whether you use K or ºC, answer is the same. Take a look again:

Delta T = T_final - T_start = (105 + 273) K - (100 + 273) K = (105 - 100) K + (273 - 273) K = 5 K

273 just cancels out.

[sameeralord]

Hello. I haven't learned these stuff at school yet but looking at the formulas and stuff I think you should add 273. The question asks for it
J mol-1 K-1. What you have done is J mol-1 C-1.

A temperature change in K is exactly the same as a temperature change in C, there is no need to add 273 to anything.

You are right . Thanks for pointing out the mistake .Sorry about this.

Let's assume T_start = 100 ºC, T_final = 105 ºC.

Delta T = T_final - T_start = 105 ºC - 100 ºC = 5 ºC

Now in Kelvins: T_start = 100 + 273 = 373 K, T_final = 105 + 273 = 378 K.

Delta T = T_final - T_start = 378 K - 373 K = 5 K

No matter whether you use K or ºC, answer is the same. Take a look again:

Delta T = T_final - T_start = (105 + 273) K - (100 + 273) K = (105 - 100) K + (273 - 273) K = 5 K

273 just cancels out.

Yeap I got it. So why is the answer A then...

[Borek]

Yeap I got it. So why is the answer A then...

Correct answer is D. The real question is, why does the teacher insist A is OK. But that's not a chemistry nor physics question.

[DrCMS]

actually, i tried, and my answer wrong, asked my teacher, he insisted that A is the correct answer, just that i didn't show here

Q = n x c x T

Q = heat evolved
n = number of moles
c = molar heat capacity
T = change in temperature


5 = (1.5 / 58.9 ) x c x 3.42

c = 57.4

Your answer is correct and your teacher is an idiot.

[monarchus]

Yeap I got it. So why is the answer A then...

Correct answer is D. The real question is, why does the teacher insist A is OK. But that's not a chemistry nor physics question.

hey, this is one of my chemistry test questions.
and i am sure that i studied this in physics
then what makes it neither a chemistry nor physics question?

[monarchus]

actually, i tried, and my answer wrong, asked my teacher, he insisted that A is the correct answer, just that i didn't show here

Q = n x c x T

Q = heat evolved
n = number of moles
c = molar heat capacity
T = change in temperature


5 = (1.5 / 58.9 ) x c x 3.42

c = 57.4

Your answer is correct and your teacher is an idiot.

please dont say this, he is a good teacher though he got this question wrong...

and thank you very much for giving me your opinion

[DrCMS]

It should have been obvious to anyone looking at the question that the answer had to be about the same as the atomic weight of cobalt. 

5J/3.42°C and 1.5g nearly cancel out so as a multiple choice question I did it in my head to get D as the only possible answer.  I looked up the weight of cobalt and used a calculator to double check the answer.

If you teacher insisted the answer was A he's a fool as it only takes a minute to prove D is correct.

[sjb]

Could you ask your teacher to show his working? 

[monarchus]

Could you ask your teacher to show his working? 

his reason for the answer is A is that he thinks that degree celsius cannot be equal to Kelvin, just that. i told him, but he didn't seem to accept my explaination.. well, anyway, it is good enough to know that this question should be done in this way... tq very much

[DrCMS]

his reason for the answer is A is that he thinks that degree celsius cannot be equal to Kelvin, just that. i told him, but he didn't seem to accept my explaination..

I go back to my earlier statement your teacher is an idiot. 

∆T in °C ≡ ∆T in K