Calculate ΔHrxn for Liquid -> Solid Water at -5°C

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The discussion focuses on calculating the heat change (ΔHrxn) for the phase transition of water from liquid at 5°C to solid at -5°C. The relevant equations include specific heat capacities for liquid and solid water, as well as the enthalpy of fusion. The initial calculations provided resulted in an incorrect total heat change, prompting a review of the sign conventions used in the calculations. It is emphasized that heat is being removed during the transition, necessitating negative signs for the temperature changes. The correct approach leads to a final ΔHrxn value of -2.95E-4 J.
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Homework Statement


What is the heat change in J associated with 80.7 g of liquid water at 5.00 ° C changing to solid water at -5.00 °C?


Homework Equations


c(H2 O) (liq) = 4.184 J/(g.K)

c(H2O) (s) = 2.09 J/ (g.K)

DHfus(H2 O) = 6.02 kJ/mol


The Attempt at a Solution


Δt = 5°

While liquid
(80.7g)(4.184J/g.k)(5°) = 1688.2 J
(-6.02kJ/mol)(80.7/18 = 4.48 mol) = -27.0 kJ
(80.7g)(2.09J/g.k)(5°)= 843.3 J

2531.5 - 27000
-2.44E4
(correct answer is -2.95E-4)

I mean I was pretty sure that is how you went about doing this type of problem :/.
The Δt = 5° came from (5 - 0) (and 0-(-5))
 
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I believe you are messing up in your sign convention. You are removing heat throughout this process and thus all of your signs must be negative. Delta T is -5, not 5.
 

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