Cliffs AP Chemistry, 3rd Edition

7. (B)

Silicon, in order to bond four hydrogen atoms to itself, must exhibit sp^3 hybridization.

8. (D) Two of the four valence electrons would go to the σ 2 sbonding orbital, and the other
   two would go to the v 2 s*antibonding orbital. The electron configuration would be
   2 ss
   2
   2

2

^vvh ` )j.

9. (E) “Normal” means 1 atm (760 mm Hg) pressure. Boiling occurs at a temperature at
   which the substance’s vapor pressure becomes equal to the pressure above its surface. On
   this phase diagram, at 1 atm pressure, there is no intercept on a line separating the liquid
   phase from the gas phase. In other words, carbon dioxide cannot be liquefied at 1 atm
   pressure. It is in the liquid form only under very high pressures. At 1.0 atm pressure, solid
   CO 2 will sublime — that is, go directly to the gas phase.


10. (C) The critical point is the point at which the liquid — gas curve ends at a point at which
    the temperature and pressure have their critical values. Critical temperature is the tempera-
    ture above which the liquid state of a substance no longer exists. Critical pressure is the
    pressure at the critical temperature.


11. (B) All three phases are in equilibrium at the triple point. The solid CO 2 sublimes if
    warmed at any pressure below 5.1 atm. Above 5.1 atm, the solid melts if warmed.


12. (A) The greater the disorder of the system, the larger the entropy. There is an increase in
    the number of molecules and thus greater disorder.


13. (A) Entropy increases upon expansion. The molecules under 1.0 atm of pressure are more
    free to move around — less constricted.


14. (A) Sublimation means the change from the ordered solid phase to the random gas phase.


15. (C) There are three molecules on the left for every two on the right. Things are becoming
    more ordered on the right.


16. (B) The system is in equilibrium. The rate of the forward reaction equals the rate of the re-
    verse reaction. No one particular side is becoming more (or less) ordered than the other.
    No additional stress is being placed on the system.

homonuclear

2 s

Be 2

2 s

s*

s

H

Si

H

H H

Part IV: AP Chemistry Practice Test