Differential and Integral Heat of Solution

ADVANCED LABORATORY I FALL, 2000 ADIABATIC CALORIMETRY Reference: S,G,&N Exp. 8 in Chp. VI. Objectives: (1) Determine the integral heat of solution for finite amounts of KNO3 dissolved in water. Extrapolate the measurement to infinite dilution to obtain the differential heat of dilution. (2) Incorporate the concepts learned in your Electronics laboratory to amplify and accurately measure temperature changes associated with solution formation. (3) Use the A/D capabilities of a computer to record voltage as a function of time (e.g. a strip chart recorder). Pre-lab assignment and questions: (1) Thoroughly read the "Principles of Calorimetry" section of Chp. VI (pgs. 145 - 151). (2) After thoroughly analyzing the circuits described in Chapter XVII of your textbook, describe in detail how the operational amplifier circuit used in this experiment works. Be sure to consider both parts of the circuit, and how they work in combination. If dRT /dT is approximately 100 (ohms per °C) what do you expect the voltage change (Vo ) to be for a 10o C temperature change? Assume the following values of voltages and resistances: V1 = -50 mV; RH = 2 kΩ; RF = 100 kΩ; R2 = 1 kΩ. By analysis of the circuit, you know the relationship between RH and R1 before an addition of KNO3. (3) Prepare your pre-lab abstract as described in your syllabus. Background: (I) Heats of Solution. In this experiment the adiabatic calorimeter is used to measure the heat of solution of KNO3 in water. The generalized reaction for this solvation is: A + x S → A xS (solution at m concentration) Where: A is pure solute S is pure solvent which is mixed to form a solution m is the molal concentration.

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The change in enthalpy accompanying this reaction depends upon the final solution concentration. Two measures of enthalpy have proved useful in determining the heat of solution: the integral heat of solution and the differential heat of solution. The integral heat of solution 1

per mole of solute dissolved Δ Hint is