In a closed environment, the vapor pressure and external pressure can vary depending on the temperature and the substances involved. Let's consider the example of a pressure cooker to understand the concept.
In a pressure cooker, the external pressure is the pressure exerted by the surroundings on the cooker's walls. This pressure is typically atmospheric pressure, which is approximately 1 atmosphere (atm) at sea level. However, the external pressure can be adjusted by altering the cooking environment (e.g., at higher altitudes, the atmospheric pressure is lower).
The vapor pressure, on the other hand, is the pressure exerted by the vapor of a substance in equilibrium with its liquid phase. It depends on the temperature and the nature of the substance. As the temperature increases, the vapor pressure tends to increase as well.
At 25°C, the vapor pressure inside the pressure cooker would depend on the substance being heated. Different substances have different vapor pressures at a given temperature. Assuming water is the substance being heated, its vapor pressure at 25°C is relatively low, around 0.0313 atm.
At 100°C, the boiling point of water at sea level, the vapor pressure of water is equal to the external pressure, which is typically 1 atm. This is the point at which the liquid water inside the pressure cooker reaches its boiling point and starts converting into vapor.
At 120°C, the vapor pressure of water increases beyond 1 atm. Consequently, the vapor pressure exceeds the external pressure, and the water boils at a temperature higher than its normal boiling point. This increase in boiling point is a result of the higher external pressure being applied to the water.
In summary, the vapor pressure and external pressure in a closed environment, such as a pressure cooker, can be different at different temperatures. The vapor pressure depends on the nature of the substance and increases with temperature, while the external pressure is typically atmospheric pressure but can be adjusted based on the surrounding conditions.