Molar heat capacity
Started by jdla
Did you round any of the given values? Because it seems to me you would just multiply the C of Fe times the g/mol of Fe. Thus, netting 77,000 cal/mol. I don't think the mass of the wire has anything to do with it since it's asking for something that's indepedent of the mass you currently have. (molar heat capacity is the energy required to raise the temperature of 1 mole an object 1degree celsius)
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Remember to use dimensional analysis. For this problem you need to look at your units and see what they want.
The answer is in (k)cal/mol, you're given cal/g and g/mol, so multiplying them would eliminate g and leave you with cal/mol.
And the molar heat capacity is not dependant on the amount of the substance, so the weight of the wire doesn't matter.
No because you're finding the molar value, meaning the amount per mol of substance.
The answer is in (k)cal/mol, you're given cal/g and g/mol, so multiplying them would eliminate g and leave you with cal/mol.
And the molar heat capacity is not dependant on the amount of the substance, so the weight of the wire doesn't matter.
jdla said:
No because you're finding the molar value, meaning the amount per mol of substance.
The MCAT is about rounding and approximations...
I found the fastest way was to:
Realize you have .006 of a gram and the heat capacity of 1 gram is 1400.
Use propotions:
X/.0068g = 1400/1g (cross mult and divide with rounding)
X*1=1400*.001 (.001 for easy units) X=1.4 Cal/g
Now convert to moles by 1.4cal/g * 55g/mol = ~70 and you rounded down earlier so look for a larger answer.
And an easy check is eliminate answers:
A 1.4kcal/mol (1.4 kcal/mole (way off cuz 1 gram has 1.4kcal/g)
B. 9.5 cal/mol (your answer was rounded down and far from this)
C. 25 cal/mol (" " "...)
D. 78 cal/mol (very close to your approx!)
I found the fastest way was to:
Realize you have .006 of a gram and the heat capacity of 1 gram is 1400.
Use propotions:
X/.0068g = 1400/1g (cross mult and divide with rounding)
X*1=1400*.001 (.001 for easy units) X=1.4 Cal/g
Now convert to moles by 1.4cal/g * 55g/mol = ~70 and you rounded down earlier so look for a larger answer.
And an easy check is eliminate answers:
A 1.4kcal/mol (1.4 kcal/mole (way off cuz 1 gram has 1.4kcal/g)
B. 9.5 cal/mol (your answer was rounded down and far from this)
C. 25 cal/mol (" " "...)
D. 78 cal/mol (very close to your approx!)
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