Handwrite everything in the picture THEORY. The standard enthalpy of combustion for a substance is defined as the enthalpy change AH° which accompanies a process in which the given substance undergoes reaction with oxygen gas to form specified combustion products [such as CO2(g), H2O(1), N2(g), SO2(g)), all reactants and products being in their respective standard states at the given temperature T. Thus the standard enthalpy of combustion of benzoic acid at 298.15°K is AH° 298. 15 for the process CeHsCO2H(s) + 15/202(g) = 7CO2(g) + 3H20(1) (1) with reactants and products in their standard states for this temperature. As will be shown below, the enthalpy of combustion can be calculated from the temperature rise, which results when the combustion reaction occurs under adiabatic conditions in a calorimeter. It is important that the reaction in the calorimeter take place rapidly and completely. To this end, the material is burned in a steel bomb with oxygen under a pressure of about 25 atm. A special acid- resistant alloy is used for the construction of the bomb because water and acids are produced in the reaction. In the adiabatic-jacket bomb calorimeter the bomb is immersed in a can of water fitted with a precise thermometer. This assembly is placed within an outer water- filled jacket. Both before and after the combustion occurs, the jacket temperature is maintained (by external means) at the same value as that of the water in the can. If the temperatures are matched with sufficient accuracy, the can and contents do not gain or lose energy by radiation or conduction and the process is therefore adiabatic. This method affords convenience in work of moderate accuracy, but there is inevitably some error due to time lag in adjustment of the outer-jacket temperature. For the most exacting research measurements, an isothermal jacket is used and accurate cooling corrections are made.[1-3a,4] It should be recognized that the process, which actually takes place in the calorimeter, does not correspond exactly to one of the type of Eq. (1) in the actual calorimeter process, the final and initial temperatures are not equal, and the reactants and products are not in their standard states. Products at pressure P
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
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