Ex_3B_KEY.pdf

# N liquid c liquid t liquid n solid 2534 mol2942 j mol

• Test Prep
• 8

This preview shows pages 7–8. Sign up to view the full content.

= n liquid C liquid T liquid n solid = (2.534 mol)(29.42 J mol K )(83 K) (1.298 mol) = 4.767 × 10 3 J mol = 4.77 kJ mol If you solve for the q liquid part first, that should be 6.188 × 10 3 J.

This preview has intentionally blurred sections. Sign up to view the full version.

NAME:_________________________________ © 2015 L.S. Brown B9 (10 pts) 8. Some “hot packs” are based on the exothermic dissolution of calcium chloride in water. CaCl 2 (s) Ca 2+ (aq) + 2 Cl (aq) Δ H ° = –81.3 kJ A particular hot pack contains 40.0 g of CaCl 2 and 175.0 g of water, originally separated by a partition. When the pack is squeezed, the partition breaks and the CaCl 2 dissolves in the water. If the pack and its contents are initially at 21.0 ° C, what is the maximum temperature that this bag could reach? (Assume that the calcium chloride solution has a specific heat of 4.20 J g –1 K –1 , and that the heat capacity of the bag itself is small enough to be neglected.) I’ll start by finding q (or Δ H) for the amount of CaCl 2 dissolving. Note that the given value for Δ H is for dissolving 1 mole, so for our 40.0 g sample we will get: Δ H = 40.0 g × 1 mol 110.98 g × –81.3 kJ 1 mol = –29.303 kJ That will be the amount of energy we have available to heat up the solution. And there will be 215 g of solution, since it includes both the 40 g of CaCl 2 and the 175 g of water. We can find Δ T: q = mc Δ T, so Δ T = q mc = 29,303 J (215 g)(4.20 J g ° C ) = 32.5 ° C We started at 21 ° C, so the final T will be 53.5 ° C.
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern