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THE STRUCTURE AND FUNCTION OF A CALORIMETER
A calorimeter is a device , or machine , used for calorimetry . Calorimetry is the process of measuring the heat of a chemical reaction or the physical changes as well as the heat capacity .
Some of the common types of calorimeters include :
• Differential Scanning Calorimeters ( Based on thermo-analytical methods , where the difference in the amount of heat required for increasing the temperature of a sample and reference is measured as a function of temperature . There are two sub-types - heat flux differential scanning calorimeters and modulated temperature differential scanning calorimeters ).
• Isothermal Titration Calorimeter ( They are used primarily to determine thermodynamic parameters fo reactions in a solution . They are used to study the binding of small molecules with larger macromolecules .)
• Accelerated Rate Calorimeters
• Bomb Calorimeters ( A contant-volume calorimeter . Measures the internal energy change between reactants and products . They have the ability to withstand large pressure while the reaction is being measured .)
A simple calorimeter just consists of a thermometer attached to a metal container full of water suspended above a combustion chamber .
To find the enthalpy ( heat change ) of a substance ( samples like oil and coal ) the sample is added to a calorimeter and the initital and final temperature ( before the reaction starts and after the reaction finishes ) are noted and recorded . The DDS Calorimeters range does this calculation so the operator won ’ t need to make manual calculations . The temperature change is multiplied by the mass and the specific heat capacity of the substance gives a value for the energy given off or absorbed during the reaction . This manual method and calculation is mainly used in academic teaching when learning the theory of calorimetry .
Three different techniques can be applied to calorimetry : temperature change ( adiabatic / isoperibol ) in which the temperature change of the calorimeter measuring cell can be converted to heat change of the reaction occurring in the calorimeter , power compensation ( isothermal ) in which the reaction and a controlled heater act as two heating sources and are kept at the same heating power so the heat change is equal to the integration of the controlled heat power over the measurement time ; and heat conduction where the temperature change caused by the heat produced in a reaction is recorded as a small voltage through heat flow sensors .
A bomb calorimeter consists of a small cup ( crucible ) used to contain the sample of oil , fuel or coal , pressurized oxygen ( either via manual or automatic oxygen filling ), a stainless steel bomb vessel ( screw cap or bayonet vessel ), water ( the DDS Calorimeters systems are waterless ; the water being replaced by insulating polystyrene or automatic temperature control ), a stirrer , a thermometer ( the DDS Calorimeters bomb vessels have built in linear temperature sensors ), and the insulating container to prevent heat flow from the calorimeter to the surroundings , and an ignition circuit connected to the bomb vessel . By using stainless steel for the bomb vessel , the reaction will occur with no volume change observed .
DDS Calorimeters | Feb / March 2017 Issue www . ddscalorimeters . com