4. In the molecules CH, NH3 and H2O, the bond angles are as follows: H-C-H
H-N-H
H-O-H
109.5°
107°
104.5°
All of these molecules have four pairs of electrons arranged around the central atom in a
tetrahedral arrangement. Explain why the bond angles are different.

Solid tin exists in two forms: white and gray. for the transformation sn(s, white) → sn(s, gray) the enthalpy change is -2.1 kj/mol and the entropy change is -7.4 j/(mol*k). a. calculate the gibbs free energy change for the conversion of 1.00 mol white tin to gray tin at -30℃. b. will white tin convert spontaneously to gray tin at -30℃? c. at what temperature are white and gray tin thermodynamically equivalent at a pressure of 1 atm?