Chemistry???

Question

What occurs at the molecular level when a liquid-vapor equilibrium exists?

A. The number of molecules in the liquid state equals the number in the vapor state.
B. The molecular changes at a liquid-vapor equilibrium depend on the temperature.
C. The rate of molecules overcoming attractive forces is equal to the rate of molecules entering the solid state.
D. Each molecule spends half the time as a liquid and half the time as a vapor.
E. The changes between liquid and vapor stop, and the amount of each becomes fixed.

Answer 1

B is correct

A is false since the equilibrium can be established at different temperatures and the number of liquid or vapor molecules depends on temperature.

B is true because the higher the temperature the more vapor molecules and the lower the temperature the more liquid molecules.

C is false because the definition of equilibrium is when the forward process and the reverse process both occur at the same rate. In this case it says "solid" state which is not one of the liquid-vapor processes.

D is false since there is no way to predict how much time each molecule spends in one state. We simply find the average for all the molecules.

E is false since an equilibrium is dynamic. The molecules do not stop moving at all. That means the exchange does not stop - it just keeps going at the same rate.

Answer 2

I think it's B.

When the temp rises in a liquid, the molecules gain energy and they move quicker and quicker and eventually break free from each other and overcome the pressure of the atmosphere above the liquid, becoming gaseous. This all depends on how hot the liquid gets. At equilibrium, some are becoming gas, some gas is falling back into liquid, and by definition, the RATES of the reverse and forward reactions in an equilibrium state (gas to liquid, liquid to gas) are equal.

It does not necessarily mean that the quantity of each gas or liquid in each forward or reverse reacton is equal (rule out A), or that they spend equal times back and forth as liquid or vapor (rule out D). Since there is a constant back and forth change from gas to liquid at the same rate, rule out E because there is constant change occurring, just equally back and forth. In C, we're already past the solid phase, so it doesn't figure in.

Answer 3

c would be correct if the penultimate word was "liquid".