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what is vapoure pressure?
Vapor pressure is the amount of pressure within a vapor or gas when the substance is in an equilibrium state. In other words, when a liquid or solid is in a closed container and some molecules evaporate while others return to the liquid or solid state, the pressure that can be measured within that container relates to the vapor. Vapor pressure is expressed in terms of atmospheres (atm) and may be affected by temperature changes, container size and molecular bond strength.

When water transforms into steam and the steam is trapped in a container, the water vapor pressure will increase until it reaches a point of equilibrium. At that point, the rate of evaporation is equal to the rate of condensation. In other words, when steam is captured in a closed area, the rise in temperature resulting from an increase in steam leads to condensation inside the container. The water molecules are trapped within the container walls and cannot escape. As a result, the molecules begin to collide and bond and return to a liquid state.


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