February 11, 2016

Homework Help: Chemistry

Posted by Don on Tuesday, February 1, 2011 at 2:33am.

Instant cold packs used to treat athletic injuries contain solid NH4NO3 and a pouch of water. When the pack is squeezed, the pouch breaks and the solid dissolves, lowering the temperature because of the following endothermic reaction.
NH4NO3(s) + H2O(l) = NH4NO3(aq) H = +25.7 kJ

What is the final temperature in a squeezed cold pack that contains 50.0 g of NH4NO3 dissolved in 115 mL of water? Assume a specific heat of 4.18 J/(gC) for the solution, an initial temperature of 25.0C, and no heat transfer between the cold pack and the environment. To find the mass of water use the density of water = 1.0 g/mL. Hint: The process takes place at constant pressure.

So i know at constant pressure i have to use

Cs * M of solution * deltaT = -(molesNH4NO3)*DeltaH of reaction

Can someone please set this problem up because I tried to set it up but had difficulties with some of the values.

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