31. 半徑R之鉛球鏤空成一空心球型如右圖。鏤空後剩餘部份之質量M。若鉛球上各部份質量均勻，則此鉛球外質量m之質點所受鉛球之重力為何？

6. Given that the enthalpy required to convert CHCl3(g) to gaseous C, H, and Cl atoms is 1397 kJ/mol and that the dissociation enthalpy of a C-H bond is 413 kJ/mol, what is the bond dissociation enthalpy of a C-Cl bond？ (A)328 kJ/mol　(B)603 kJ/mol　(C)984 kJ/mol　(D)1397 kJ/mol