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

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SUMMARY

The heat change (ΔHrxn) for the phase transition of 80.7 g of liquid water at 5.00 °C to solid water at -5.00 °C is calculated using specific heat capacities and the enthalpy of fusion. The specific heat of liquid water is 4.184 J/(g·K) and for solid water is 2.09 J/(g·K). The enthalpy of fusion (ΔHfus) for water is 6.02 kJ/mol. The total heat change is determined to be -29,500 J, correcting for sign conventions during the cooling and phase change processes.

PREREQUISITES
  • Understanding of specific heat capacity (c) for both liquid and solid states of water.
  • Knowledge of the enthalpy of fusion (ΔHfus) for phase changes.
  • Ability to perform calculations involving mass, temperature change (Δt), and moles.
  • Familiarity with thermodynamic sign conventions for heat transfer.
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  • Study the calculation of heat changes during phase transitions using specific heat and enthalpy values.
  • Learn about thermodynamic principles related to heat transfer and sign conventions.
  • Explore the concept of molar mass and its application in thermodynamic calculations.
  • Investigate other phase change calculations, such as vaporization and sublimation of water.
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Chemistry students, educators, and professionals involved in thermodynamics, particularly those focusing on phase transitions and heat calculations in water.

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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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