Chemical Reactions

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<strong>Chemical</strong> Energy from Process This session deal with the chemical energy within the molecules of a closed system that involve a chemical reaction. During a chemical reaction, some chemical bonds that bind the atoms into molecules are broken and new ones are formed. The chemical energy associated with this process is usually different for the reactants and products. 393,520 kJ 1 kmol C at 25 o C, 1 atm Combustion Chamber CO 2 at 25 o C, 1 atm 1 kmol H at 25 o C, 1 atm 241,820 kJ Combustion Chamber H 2 O (g) at 25 o C, 1 atm 1 kmol O 2 at 25 o C, 1 atm 1 kmol O 2 at 25 o C, 1 atm First Law of Thermodynamics The first law of thermodynamics states that in any closed system, energy is conserved. Which means that energy cannot be created nor destroyed, but it can only change forms. Meaning: ∆E sys = 0 and ∆E products =-∆E reactants The molecules of a closed system possess energy in various forms such as sensible and latent energy, chemical energy, and nuclear energy. All of these forms must balance out in the reactants and products to give the system a net energy of zero. 8
Enthalpy Change Enthalpy is the system we use to measure that change in energy of a closed system due to chemical bonds being broken. Reaction enthalpies are real physical quantities for which numeric values can be calculated or measured. In order to put the calculation into algebraic form, chemists use the defined equation: ∆H = Σ∆H f (products) -Σ∆H f (reactants) The reaction enthalpy, which is the enthalpy change that occurs in the reaction, is always calculated as the sum of the enthalpies of the products minus the sum of the enthalpies of the reactants. Standard Reference State Since composition of a system at the end of a process is no longer the same as that at the beginning of the process, there’s a need to use a standard condition in which to make the measurements from. This standard condition is called the standard reference point, which are 25 o C and 1 atm. The superscript “ ° ” is used to indicate property values at the standard state. The defined equation above, under standard conditions, becomes: ∆H ° = Σ∆H ° f(products) -Σ∆H ° f(reactants) 9
Page 1 and 2: Chemical Reactions Objectives: •A
Page 3 and 4: 1 kmol C + 1 kmol O 2 1 kmol of CO
Page 5 and 6: Theoretical and Actual Combustion P
Page 7: Example 15.3 combustion of gasous f
Page 11 and 12: Table A-26 A Enthalpy of Formation
Page 13 and 14: Heating Value of Fuel = the amount
Page 15 and 16: Example 15.6 First Law Analysis of
Page 17 and 18: (a) Combustion equation: CH 4 (g)+
Page 19 and 20: Example 15.8 Adiabatic Flame Temper
Page 21: Assume air and combustion gases are

Chemical Reactions

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