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| Vapour Pressure of Liquids |
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| Vapour pressure is defined as the partial pressure exerted by the vapors above the liquid surface in equilibrium with liquid at a given temperature. |
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| fig 3.3 |
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| In illustrations 1a and 1b, the liquid and vapor states of a given substance are represented. The individual molecules or particles are represented at a particular instant of their random motion. When equilibrium is reached (illustration 1c), the number of molecules evaporating is equal to the number of molecules condensing. The pressure read on the manometer M is the vapor pressure of the liquid at that temperature. |
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| Vapor pressure of a liquid depends on the following factors: |
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| a) Nature of the liquid |
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| b) Temperature of the liquid. |
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| Nature of the liquid |
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| Liquids that have weak intermolecular forces are more volatile and have a higher vapor pressure. |
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| For e.g., vapor pressure of ethyl alcohol is greater than that of the water. |
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| Temperature of the liquid |
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| Vapor pressure increases with increase in temperature. This is because with an increase in temperature, rate of evaporation also increases. |
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