In general, how do the intermolecular attractions between particles in a gas....?

1. The intermolecular attractions between liquids is definitely higher than that of gas particles. That's what makes it a liquid, as oppose to a gas. Liquid particles become gas particles when its particles have enough energy to break away from the intermolecular bonds and become gas (such as liquid water being heated to evaporation). Gases are also farther away from each other, so there is less attractions between the molecules.

2. A dynamic equilibrium exists when the forward and reverse reaction occurs at equal rates, meaning there is no net change. Thus, for the open beaker, vapor will form once in a while when a liquid particle gets enough energy and break out of the liquid phase to become a vapor. But keep in mind that water vapor in the air may also get trapped inside the liquid. So dynamic equilibrium can be achieved when the rate of liquid becoming vapor and vapor becoming liquid is the same.

3. Evaporation is basically a way to decrease temperature. When liquid water is heated, the particles in the liquid gains energy and start bumping into other particles, until it finally gets enough energy and become a vapor. And when that particle leaves, the overall temperature of the water decreases. So if the fastest runner is removed from the race, that's like saying the high energy particle is gone. Thus the average speed of the rest of the runners will decrease, this is saying the average energy for the rest of the particles will also be less (since the high energy particle will no longer be bumping into other particles).

4. For boiling point, a substance will boil when the vapor pressure is equal to the atmospheric pressure. Generally, at a given temperature, substances with lower boiling point will have a higher vapor pressure. Thus, at 75 degrees C, ethanol will be closer to its boiling point, so it will have the greater vapor pressure. Another way to think about this is: at 78.5°C, liquid ethanol will have gained enough energy and become gas particles, so at 75.0°C the vapor pressure of liquid ethanol will be closer to the atmospheric pressure then water is (since a substance will boil when the vapor pressure is equal to the atmospheric pressure).

Hope that helps.