enthalpies by Adiabatic Calorimetry Faculty: Prof. Chandra - PowerPoint PPT Presentation

TH 201: Determination of partial molar enthalpies by Adiabatic Calorimetry Faculty: Prof. Chandra Venkataraman Staff: Nirmal Karangale RajuAheda TAs: Madhusree Sarkar Sujith Das Varun Gaala

Objectives  To determine heats of mixing of binary systems by adiabatic calorimetry  To determine partial molar enthalpies of the two components  To test whether a given hypothesis holds true

Principle  Calorimetry: Involves measurement of enthalpy changes of chemical reactions or physical changes as well as heat capacity using the principle of conservation of energy.  Here adiabatic calorimetry is employed. Thus, there is no heat exchange with the surroundings.  Temperature change monitored.

Theory  Partial molar properties: Thermodynamic properties that vary with the molar composition of the components. Helps understand properties of components in a mixture.  Heat of mixing: Amount of heat exchanged when two components are mixed.

Diagram of the Setup Fig: Adiabatic Calorimeter D = Dewar Flask of capacity 150 ml, S = Polypropylene Stopper, H = Resistance Heater, ST= Stirrer, T = Temperature Sensor

Procedure

Calculations For a heating coil : Q  IVt For known amount of heat, Q (Joules) is supplied to calorimeter containing water if Δ T is the observed temperature change, then:     Q mC T K T P Combining the above equations by assuming perfectly adiabatic conditions:     IVt mC T K T P          The heat evolved due to mixing: Q mC K T m P m The heat of mixing Δ hm is given by: Q   m h  m ( n n ) 1 2 Partial molar enthalpies are given by :   d h d h     m m h h x h h x 1 m 2 2 m 1 dx dx 1 1

Results and graphs  Δ Tmix vs Mole fraction of water  Cp of mixture vs Mole fraction of water  Δ Hmix vs Mole fraction of water  Interpretation of results and graphs with uncertainties  Note: To test the hypothesis given, additional measurements/calculations may be required, e.g. Measurement and reporting of temperature with respect to time to check if the calorimeter is indeed adiabatic

Precautions  Care should be taken so that "heat leak" does not occur through either the lid of the Dewar flask or openings in the lid.  While heating, the mixture should be constantly stirred for temperature uniformity

Reporting  Introduction  Aim including the hypothesis to be addressed  Schematic of apparatus  Method  Explanation of theory  Calculation flowchart and sample calculation  Uncertainty in measured and calculated values  Findings  Plots and discussion  Interpretation  Whether hypothesis was proved true/ false  Suggest improvements in rig/calculation method

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