Monday
November 24, 2014

Homework Help: lab+chem.

Posted by David on Saturday, August 5, 2006 at 8:21pm.

Hey can u guys help on this lab, I dont get it.

I have to figure out the: prediction, Analysis, and evaluation.

Problem: what is the molar enthalpy of ice?

Evidence:
mass of calorimeter: 3.76g
mass of calorimeter+ water: 103.26g
mass of calorimeter+ water+melted ice: 120.59g
initial temperature of ice:0.0 degress celcius
initial temperature of water:
32.4 degress celcius
final temp. of water: 15.6 degress celcius


The one thing I dont get is how to do the prediction and analysis. Can you help me figure out what the molar enthalpy of fusion of ice is? Thanks!


I assume you can calculate the mass of ice and mass of H2O from the data.
(massofice*deltaHfusion)+[massof ice*specificheatmeltedice*(Tf-Ti)]+[massofwater*specificheatwater*(Tf-Ti)]=0
Plug all those values in and solve for delta H fusion. If you have trouble, post your work to the point where you are stuck and we can help you through.


I didn't define my terms. Tf is the final temperature and Ti is the initial temperature of the appropriate material (meltice ice or water).


I got the answer -338.79J/mol, would that be right? And are the units right?

(17.33*deltaHfusion) + (17.33*4.19*(15.6-0)) + (99.5*4.19*-16.8) = 0

(17.33*deltaHfusion) + (-5871.2458)=0

(-5871.2458)/ (17.33)= deltaHfusion

-338.79J/mol =deltaHfusion

Thanks*


You have used 4.19 for the specific heat of water which has the units of J/g*C. The problem asks for the units per mole, not per gram. You may use your answer and multiply by the molar mass of H2O OR go back and substitute (I think it is 75.3 J/mol) for the 4.19 you used. I think I obtained about 6.08 kJ/mol or so and that is about what you have, too. My references list 4.184 and not 4.19 for the specific heat of water. At the least, I would use 4.18 and recalculate (then multiply by 18) or use 4.18 x 18.0 and get the answer in the units requested. I hope this helps.


I just looked at the problem you worked again and I think you have a sign wrong; i.e., you have 17.33X +(-5800something) = 0. When the 5800 something is carried to the other side it becomes a + number and the answer should be a positive number. And you added heat to the ice to melt it. At any rate, check your arithmetic and see if it doesn't come out a positive number. I meant to write that the first time and it slipped my mind.


THANK YOU! If I have any more questions I will ask.


oh i jus got it sry i am only in 8th..

Answer this Question

First Name:
School Subject:
Answer:

Related Questions

Science - I am trying to find an example of how to write a prediction for a ...
Lab in general - I just read my syllabus for lab and I am kind of shocked at ...
lab.... - when doing a lab you need an anayliss, but what is it and how do I ...
12 Chemistry - What is the molar enthalpy of combustion of magnesium? This was ...
chemistry - Hey, I was just struggling with a question that I need to figure out...
Chem Lab Help - I wanted to know if any one has done the Determination of ASA ...
CHEM LAB - What is the Molar Enthalpy of Neutralization in kJ/mol if 5.00 moles ...
Chem Lab - What is the Molar Enthalpy of Neutralization (ÄHn) in kJ/mol if 5.00 ...
AP Chemistry - I need help with figuring out an appropriate way to do this sort ...
Chemistry - Why wouldn't you do this reaction directly in a lab (and would ...

Search
Members