A student performs an experiment to determine the molar enthalpy of solution of
ID: 971215 • Letter: A
Question
A student performs an experiment to determine the molar enthalpy of solution of urea and places 91.95 g of water at 25 degree C into a coffee cup calorimeter and immerse a thermometer in the water. After 50 s, the student adds 5.13 g of solid urea, also at 25 degree c, to the water and measures the temperature of the solution as the urea dissolves. A plot of the temperature data is shown in the graph below. (Specific heat capacity of pure water is 4.2 J g^-1 degree C^-1) Determine the change in the temperature of the solution that results from the dissolution of the urea. According to the data, is the dissolution of urea in water is an exothermic or endothermic process? Justify your answer. By using above data, calculate the heat of dissolution of urea in joules and also the molar enthalpy of solution Delta H degree_soln, of urea in KJ mol^-1.Explanation / Answer
A) Change in temperature = Final temperature - Initila temperature =22.8 oC - 25oC = 2.2 oC
B) The temperature is decresing, hence heat is being absorbed. hence, the reaction is ENDOTHERMIC.
C) Q = m x Cp x dT
Q = (5.13 + 91.95) x 4.2 x 2.2 = 231.74 J = heat of dissolution
No. of moles = mass/molar mass = 5.13/60 = 0.0855moles
molar enthalpy = 0.232kJ/ 0.0855 = 2.71kJ/mol
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.