Question
Please explain why for each question.
1. What is the H for the reaction given? (BDE c 285 K/mole, BDE co 401KI/mole) : Br: : OH : OH :Br A. 686 KJ/mole B. -116 KI/mole C. 116 KU/mole D. -686 KJ/mole 2. Which of the following is true for a spontaneous reaction? A· 8 c. D AH = (-), AS s (-)·T-high AH = (+)AS = (-), T = high : (+), as = (-), T-low &H; . (-), AS (+), T-high or low Carbocations are one type of reaction intermediate in which the carbon atom is electron deficient What type of carbocation is most stable? 3. A Tertiary B. Secondary C. Primary D. Methyl Which of the following is the best description regarding the bonds formed and broken in an electrophilic addition reaction? 4. One sigma bond is broken and two pi bonds are formed in its place Two pi bonds are broken and one sigma bond is formed in their place Two sigma bonds are broken and one pi bond is formed in their place One pi bond is broken and two sigma bonds are formed in its place A. B. C. D. 5. Bond breaking always requires the input of energy. Which term best describes bond breaking? A. Homolytic B. Heterolytic C. Endothermic D. Exothermic
Explanation / Answer
1. Answer : B (-116 kJ/mol)
since BDE C-Br = 285 kj/mol and BFE C-O = -401 kJ/mol then -401+285 = -116 kJ/mol
2. Answer : D
Since dG = dH - TdS if dG = -ve then the reaction is spontaneous
3. Answer : A
Since more carbon atoms are donating electron density towards carbocation.
4. Answer : D (One pi bond broken and two sigma bonds are formed)
5. Answer : C (Endothermic)