How do you do b? To get the binding energy of a water molecule, approximate it a

Question

How do you do b?

To get the binding energy of a water molecule, approximate it as two protons (ionized hydrogen atoms) joined to a negatively charged oxygen atom (with two extra electrons). The picture below shows the geometrical arrangement. Joyfully recalling your high school trigonometry, find the distance between the hydrogen atoms. Calculate the electrostatic energy of this arrangement including the sign (a negative sign means energy is released when these atoms come together). Think about how this approximation is wrong and thus which way the answer is off

Explanation / Answer

charge on each H,
q1=q2 = 1.6*10^-19 C
charge on O,
q3 = 2*( - 1.6*10^-19) = - 3.2*10^-19 C
r12 = 1.515 A = 1.515*10^-10 m
r13=r23 = 0.9584 A = 0.9584*10^-10 m

E = K*(q1*q2/r12 + q1*q3/r13 + q2*q3/r23)
=(9*10^9)*{(1.6*10^-19*1.6*10^-19/1.515*10^-10) + (1.6*10^-19 *-3.2*10^-19/0.9584*10^-10) + (1.6*10^-19 *-3.2*10^-19/0.9584*10^-10)
=9*10^9 {1.69*10^-28 -5.342*10^-28 -5.342*10^-28}
= -8.095*10^-18 J
= -8.095*10^-18 / (1.6*10^-19) eV
= -50.6 eV

Related Questions

Navigate

• Browse (All)
• Browse H
• Subjects

---

---

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