2. A student is attempting to determine the heat capacity at constan pressure (C

Question

2. A student is attempting to determine the heat capacity at constan pressure (Cp) of a colorless, odorless liquid that is miscible with ("dissolves in") water. To do so, he mixes 25 g of the unknown l at 23-C) in a glass beaker with 30 g of water that has been preheated to 80 °C. The final temperature of the mixture is found to be 58 °C Assuming that no heat is lost to the surroundings during the process described above, calculate the heat capacity at constant pressure (Cp) of the unknown liquid. Show your work for credit. Hint: Begin by applying the first law of thermodynamics for all energy changes.

Explanation / Answer

for adiabatic system,

heat gained by unknwon liquid = heat lost by water (1)

heat gained by unkown liquid = mass of liquid* specific heat of liquid* change in temperature = 25*Cp*(58-23)

where Cp =specific heat of unknown liquid.

heat lost by water= mass of water* specific heat of water* change in temperature= 30gm*4.184J/gm.deg.c*(80-58)

from Eq.1, 25Cp*35= 30*4.814*22

Cp = 30*4.184*22/(25*35) =3.155 j/gm.deg.c

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