Nitromethane, CH3NO2, can be used as a fuel. When the liquid is burned, the (unbalanced) reaction is mainly CH;NO2(1) + O2(9) → CO2(9) + N2(g) + H2O(g) a The standard enthalpy change of reaction (AHn) for the balanced reaction (with lowest whole-number coefficients) is –1288.5 kJ. Calculate AH; for nitromethane. CO2(9) H2O(g) AH = -393.5 kJ/mol AH = -242 kJ/mol AH; = kJ/mol bA 15.0-L flask containing a sample of nitromethane is filled with O2 and the flask is heated to 100.°C. At this temperature, and after the reaction is complete, the total pressure of all the gases inside the flask is 920. torr. If the mole fraction of nitrogen (xnitrogen) is 0.134 after the reaction is complete, what mass of nitrogen was produced? Mass =
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.
The balanced reaction will be written as:
4CH3NO2 (l) + 3O2(g) → 4CO2 (g) + 2N2 (g) + 6H2O (g)
These are lowest whole number coefficient of reaction.
The standard enthalpy change for (least whole number coefficient) reaction is given as:
∆Hrex=-1288.5 kJ
Further, enthalpy of formation of products and reactants are given as:
CO2 (g), ∆Hf⁰= -393.5 kJ/mol,
H2O (g), ∆Hf⁰= -242 kJ/mol,
N2 (g), ∆Hf⁰= 0 kJ/mol ( for pure molecule)
O2 (g), ∆Hf⁰= 0 kJ/mol ( for pure molecule)
Now, enthalpy change of reaction is calculated as:
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