Assume that the bond enthalpies of the oxygen-hydrogen bonds in H_2O are not sig

Question

Assume that the bond enthalpies of the oxygen-hydrogen bonds in H_2O are not significantly different from those in H_2O_2. Based on the value of Delta H degree of the reaction, which of the following could be the bond enthalpies (in kJ/mol) for the bonds broken and formed in the reaction? Which of the following accounts for the observation that the pH of pure water at 37 degree C is 6.8 ? (A) At 37 degree C water is naturally acidic. (B) At 37 degree C the autoionization constant for water, K_w, is larger than it is at 25 degree C. (C) At 37 degree C water has a lower density than it does at 25 degree C; therefore, [H^+] is greater. (D) At 37 degree C water ionizes to a lesser extent than it does at 25 degree C.

Explanation / Answer

when H2O is formed from H2 and O2, two O-H bonds are formed and one O=O is broken. whereas when H2O2 is formed, two OH bond and one O-O bond is formed while a O=O is broken. The enthalpy of formation of H2O and H2O2 will be similar only if O-O bond formation has a small value and does not contribute much to the overall enthalpy change. Answer is B.

-----------------------------------------

At 37oC auto ionization of water (Kw) has a larger value . This results in formation of more number of H+ and water is slightly acidic. Answer : B

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.