# Melting questionWatch

#1
Hi guys,

Just wondering how you do this question and whats the maths behind it, if there is any.

Which mole sample of the solids below is best for melting a 500- gram sheet of ice on a sidewalk? a. NaCl b. CaCl2 c. KBr d. AgNO3 e. NaC2H3O2

Thanks
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1 year ago
#2
You have to calculate the enthalpy of combustion which is the energy released when one mole of a substance burnd in O-O to produce CO2 + H2O and whichever has the most exothermic answer is the answer.
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1 year ago
#3
What information is given about the compounds?
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#4
Thanks! The question didnt give me any enthalpies though, so would that mean I would just have to know the answer?
(Original post by BDunlop)
You have to calculate the enthalpy of combustion which is the energy released when one mole of a substance burnd in O-O to produce CO2 + H2O and whichever has the most exothermic answer is the answer.
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1 year ago
#5
(Original post by BDunlop)
You have to calculate the enthalpy of combustion which is the energy released when one mole of a substance burnd in O-O to produce CO2 + H2O and whichever has the most exothermic answer is the answer.
No you don't.

Doesn't the melting point suppression depend on the number of mol of ions produced?

You do the math.
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1 year ago
#6
(Original post by ChemBoy1)
Thanks! The question didnt give me any enthalpies though, so would that mean I would just have to know the answer?
I'd guess e because you know a, b and c are all salts that you don't burn for heat release, d Is a salt too. I'd guess e
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1 year ago
#7
(Original post by Pigster)
No you don't.

Doesn't the melting point suppression depend on the number of mol of ions produced?

You do the math.
I didn't presume it was talking about mpt suppression, albeit I am not really familiar with this concept. I assumed we were combusting something to produce the heat, which probably wasn't the best presumption.. Apparently the dissolving of CaCL2 is exothermic, perhaps this could be a solution?
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#8
E is not the answer, the answer is B, but there is no explanation so I have no idea why its B.
(Original post by BDunlop)
I'd guess e because you know a, b and c are all salts that you don't burn for heat release, d Is a salt too. I'd guess e
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1 year ago
#9
(Original post by ChemBoy1)
E is not the answer, the answer is B, but there is no explanation so I have no idea why its B.
Look at my reply to pigster. It's to do with enthalpy change of solution
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1 year ago
#10
(Original post by ChemBoy1)
E is not the answer, the answer is B, but there is no explanation so I have no idea why its B.
The Q states that you have a mol of each.

Which salt contains the most mol of ions per mol of substance?
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#11
Thanks Pigster, so then CaCl2 would make sense then! Just out of interest by does the salt with more moles of ions be able to melt ice more easily?
(Original post by Pigster)
The Q states that you have a mol of each.

Which salt contains the most mol of ions per mol of substance?
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1 year ago
#12
The salt with the most ions causes the greatest melting point depression.

And hence makes it best at melting the ice.
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