1.- Glycine, C 2 H 5 O 2 N, is importantfor biological energy. The combustion re

Question

1.- Glycine, C2H5O2N, is importantfor biological energy. The combustion reaction of glycine is givenby the equation: 4C2H5O2N(s) +9O2(g) ----> 8CO2(g) + 10H2O(l)+2N2(g)         Horxn=-3857kJ.                                                           Given that Hof[CO2(g)] =-393.5 kJ/mol andHof[H2O(l)] = -285.8 kJ/mol,calculate the enthalpy of formation ofglycine.      a) -537.3 kJ/mol  b) -268.2 kJ/mol     c) -2149kJ/mol     d) -3178kJ/mol     e) -964 kJ/mol 4C2H5O2N(s) +9O2(g) ----> 8CO2(g) + 10H2O(l)+2N2(g)         Horxn=-3857kJ.                                                           Given that Hof[CO2(g)] =-393.5 kJ/mol andHof[H2O(l)] = -285.8 kJ/mol,calculate the enthalpy of formation ofglycine.      a) -537.3 kJ/mol  b) -268.2 kJ/mol     c) -2149kJ/mol     d) -3178kJ/mol     e) -964 kJ/mol

Explanation / Answer

4C2H5O2N(s) +9O2(g) ----> 8CO2(g) + 10H2O(l)+ 2N2(g)  ; Horxn= -3857kJ   --------- ( 1 ) Given thatHof[CO2(g)] = -393.5kJ/mol C + O 2 ---------------> CO 2 ;Hof[CO2(g)] = -393.5kJ/mol    --------------- ( 2 ) and Hof[H2O(l)] =-285.8 kJ/mol H 2 + ( 1 / 2 ) O 2 -----------------> H 2 O  ;  Hof[H2O(l)] =-285.8 kJ/mol   ----------- ( 3 ) Formation of glycine is given by 2C + O 2 + (5/2) H2 + ( 1 / 2 ) N 2 ------------> C 2 H 5 O 2N     ; H ---------------- ( 4) Eqn ( 4 ) can be obtained by 2 * Eq ( 2 ) + ( 5/2 ) * Eq( 3 ) + ( 1/4 ) reverse of Eq ( 1 ) So , H = 2 ( -393.5 ) + ( 5/2 ) ( -285.8 ) + ( 1/4 )(+ 3857 )             = - 787 - 714.5 + 964.25             = -537.25 KJ / mol             ~ - 537.3 KJ / mol So, option ( a ) is correct

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