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Thermochemistry

Question. How will you differentiate between ∆E and ∆H ? Is it true that ∆H and ∆E have the same values for the reaction taking place in the solution state? 
Answer. H is amount of heat evolved or absorbed in a reaction at constant pressure whereas ∆E is amount of heat evolved or absorbed in a reaction at constant volume. Yes it is true that both ∆E and ∆H have the same values for the reaction taking place in solution phase. This is due to fact that in solution state volume of the system remains constant. 

Question. What is the difference between heat and temperature? Write a mathematical relationship between these two parameter. 
Answer. Heat: Transfer of energy between two bodies due to temperature difference is called heat. It is represented by letter q. 
Temperature: It is measure of average kinetic energy of all particles of a system. Temperature can be used to determine the flow of heat. 

Mathematical relationship:    
                        

Where q is quantity of heat transferred, m is mass of substance to q is transferred, is difference of temperatures of the substance before and after the heat transfer. 

Question. How do you measure the heat of combustion of a substance by bomb calorimeter method? Answer. It consists of a cylindrical steel vessel lined with enamel to prevent corrosion. A known mass of the test substance is placed in a platinum crucible inside the bombe. The lid is screwed on tightly and oxygen is provided through a valve until the pressure inside is about 20 atm. After closing the screw valve, the bomb calorimeter is immersed in a known mass of water in insulated calorimeter. Then it is allowed to attain the steady temperature. Then initial temperature is noted. Then test sample is then ignited by passing currant through ignition coil. Then temperature of water, that is stirred continuously, is recorded at 30 sec. intervals. From increase in temperature , heat capacity, of bomb calorimeter including bomb, water etc, we can calculate the enthalpy of combustion.


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