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

Faculty: Prof. Chandra Venkataraman Staff: Nirmal Karangale RajuAheda TAs: Madhusree Sarkar Sujith Das Varun Gaala

TH 201: Determination of partial molar enthalpies by Adiabatic Calorimetry

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

IVt Q 

For a heating coil: For known amount of heat, Q (Joules) is supplied to calorimeter containing water if ΔT is the observed temperature change, then:

T K T mC Q

P

   

Combining the above equations by assuming perfectly adiabatic conditions:

T K T mC IVt

P

   

The heat evolved due to mixing:

   

m P m

T K mC Q     

The heat of mixing Δhm is given by:

) (

2 1

n n Q h

m m

  

Partial molar enthalpies are given by:

1 2 1

dx h d x h h

m m

  

1 1 2

dx h d x h h

m m

  

Results and graphs

 ΔTmix vs Mole fraction of water  Cp of mixture vs Mole fraction of water  ΔHmix 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

• ccur through either the lid of the Dewar flask or
• penings 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

Thank you