Outage Notification

#39.  The question is asking to calculate the heat capacity of a bomb calorimeter, and the answer key has a negative value.  Does it make sense for a heat capacity of a calorimeter to be a negative value? Even with the calculation, the temperature decreases and the delta H is negative, so the answer should be positive (??) 
#44.  Although it does not give the equation, I assume formation of ammonia means N2 + 3H2--> 2NH3.  This calculates to 975kJ for enthalpy of reaction, but the question is asking for the enthalpy of reaction for the formation of ammonia, so it should be half of 975kJ or 487.5 kJ/mol (since there are two moles of ammonia formed in the reaction).  The answer key says 975.  
#2 of Free Response...  I'm probably approaching this completely wrong, but I cannot get the answers on the key.  The answer key to part a says 22.1C, but this looks like an endothermic reaction, so the temperature should be less than initial of 20C.  Also, it says the change in energy is +52.088 J for the 0.860 mol of NaCl while in the prompt it says the heat of solution is +3.9 kJ/mol.  Not sure what to do with these two pieces of information, and wondering why the energy given is so much lower than what you would expect from the heat of solution.  Also, the problem seems unrealistic to dissolve 0.86 mol of NaCl (50g) in 5.5 mol of water (99mL).  In part b, question says you are using a solvent that creates a higher heat of solution (not sure what that means– the lectures didn’t really address heat of solution) and if the temperature change will be larger or smaller. Then it says assume delta H is the same.  If the delta H is the same, wouldn’t the temperature also be the same?  In the answer key, it says the denominator is greater, that is why there is a less change.  I think we are supposed to use the equation delta T = q/mc.  Why is the denominator greater? Isn’t the q value larger if there is a greater heat of solution? 
#3 of Free Response part a and b is asking for DH, which I was not sure what it meant.  I think I realized later it might mean delta H.  Is that correct?  Does part a supposed to have a list of bond energies?  I looked them up, and the values vary a little, but I calculate -346kJ, which is not the same as the key.  In part c and part d, it is asking to use the enthalpy change in part c.  I think you mean part b?

Hi Yoko,
Thank you for your comments.  They are very helpful. You are correct for #39, the answer has been revised to reflect a +50kJ.  For #44 the question has been revised to ask for the answer to be per mole and the answer reflects half the original enthalpy. I replaced Free response #2 with a question more reflective of the content. For Free response #3 I added a table of needed bond enthalpies and created answers that reflect this change. I also replaced the DHs and  referenced to part b in parts c and d