A10.0 g sample of lioh is dissolved in 120.00 g of water at 23.0â°c in a coffee-cup calorimeter with a heat capacity of 100 j/â°c. the heat capacity of the solution was 4.20 j/gâ°c, and final temperature was 34.65â°c. based on these measurements, what is the enthalpy of dissolution of lioh in kj/mol?

-15.24 kJ/mole of LiOH

Explanation:

General considerations:

-A coffee-cup calorimeter is a device that works at constant pressure. Since enthalpy (ΔH) is defined as a heat flow at constant pressure, the coffee-cup calorimeter is usually used to measure enthalpy changes in processes at constant pressure.

-The high heat capacity of calorimeter indicates its difficulty to vary its temperature.

-The calorimeter absorbs a negligible amount of heat.

Information given in the statement:

Intial temperature = 23°C

Final temerature = 34.65°C

Mass of LiOH= 10 g LiOH

Mass of solution =  

Specific heat capacity of the solution =  

Converting specific heat capacity to kJ/(g°C) =" alt="\frac{4.20 J}{g°C}=\frac{4.20 J}{g°C}*\frac{1 kJ}{1000 J}=\frac{0.00420 kJ}{g°C}" />" />

Calculations:

To determine the dissolution enthalpy of LiOH, we can use the following equations:

 Equation 1

 Equation 2  

 = enthalpy of dissolution per mole of LiOH (kJ/mole).

= heat released  by dissolution (kJ).  

=heat absorbed by the solution in calorimeter (kJ) .

m=mass of solution (g).

C=specific heat capacity of the solution (kJ/g°C).

ΔT=chage of temperature of the solution in calorimeter, final temperature minus initial temperatrue (°C).

Molecular weight of LiOH=23.95 g/mole  

Replacing the given data in equations 1, 2 and 3, we get:

Note: Usually exothermic reactions like LiOH dissolutions, that release heat, results in negative enthalpy.

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