Water evaporates under atmospheric pressure. Without changing the temperature, the same water is placed in partial vacuum. The rate of evaporation will

Options

A. increase
B. drop to zero
C. decrease
D. remain unaffected

Answer

To solve the question regarding the effect of placing water in a partial vacuum on its rate of evaporation, we can follow these steps:

### Step 1: Understand the concept of evaporation
Evaporation is the process where liquid water turns into vapor at a temperature below its boiling point. It occurs at the surface of the liquid and can happen at any temperature.

**Hint:** Remember that evaporation occurs at the surface of the liquid and is influenced by external conditions.

### Step 2: Consider the effect of atmospheric pressure
Under normal atmospheric pressure, the rate of evaporation is determined by the balance between the vapor pressure of the liquid and the surrounding atmospheric pressure. When the vapor pressure of the water equals the atmospheric pressure, evaporation occurs at a certain rate.

**Hint:** Think about how atmospheric pressure affects the ability of water molecules to escape into the air.

### Step 3: Analyze the situation in a partial vacuum
When water is placed in a partial vacuum, the pressure above the water decreases. This reduction in pressure allows water molecules to escape more easily into the vapor phase because there are fewer air molecules exerting pressure on the surface of the water.

**Hint:** Consider how lowering the pressure affects the energy and movement of water molecules at the surface.

### Step 4: Conclude the effect on the rate of evaporation
Since the vapor pressure of the water remains constant (as the temperature is unchanged), the decrease in external pressure (due to the partial vacuum) means that the rate of evaporation will increase. This is because there are fewer obstacles for the water molecules to escape into the vapor phase.

**Hint:** Remember that a lower pressure environment facilitates the transition of water from liquid to vapor.

### Final Answer
The rate of evaporation will **increase** when the same water is placed in a partial vacuum without changing the temperature.