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Raoult's Law

The human bod...

Question

The human body has an average temperature of 98°F. Assume that the vapour pressure of the blood in the veins behaves like that of pure water. Find the minimum atmospheric pressure which is necessary to prevent the blood from boiling. Use figure of the text for the vapour pressures.

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Solution

Here,
T = 98⁰F

$\begin{array}{l} {When we convert the temperature to}^{0} C, we get \\ \frac{5}{9} (F - 32) \\ = \frac{5}{9} (98 - 32) \\ = {36.7}^{0} C \end{array}$

We drop perpendicular corresponding to a temperature of 36.7⁰C on Y-axis from the curve of pure water. This gives the boiling point of blood 50 mm of Hg.

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Similar questions

Q. The vapour pressure of an aqueous solution is found to be

750 torr

at certain temperature

^{'} T^{'}

^{'} T^{'}

is the temperature at which pure water boils under atmospheric pressure and same solution show elevation in boiling point

Δ T_{b} = 1.04 K

, find the atmospheric pressure

(K_{b} = 0.52 {k kg mol}^{- 1})

Q. The vapour pressure of an aqueous solution is found to be 750 torrs at certain temperature 'T'. If 'T' is the temperature at which pure water boils under atmospheric pressure and same solution show elevation in the boiling point

Δ T_{b} = 1.04 K

, find the atmospheric pressure?

[K_{b} = 0.52 K k g m o l - 1]

The water boils when :

1.Saturated vapour pressure of water becomes equal to atmospheric pressure

2. Boiling point of water becomes more than atmospheric pressure

3. Saturated vapour pressure of water is less than atmospheric pressure

4. Vapour pressure of water becomes more than atmospheric pressure

Comprehension # 2

Following passage explains the effect of temperature on the vapour pressure of the liquid.

Effect of temperature on vapour pressure

The quantity of heat required to evaporate a given liquid at constant temperature is defined as the heat of vaporisation. Variation of vapour pressure with temperature is given by,

Clausius-Clapeyron equation.

l o g_{e} P = - \frac{Δ H_{v a p}}{R T} + l o g_{e} A

A liquid is said to be at its boiling temperature if its vapour pressure is equal to external pressure. Therefore, the boiling point of water in particular and of liquids in general decreases as an altitude of a place increases where the external pressure is less than

1 a t m o s p h e r e

(normal b.p. of water is

373.15 K

1 a t m o s p h e r e

On top of mount everest, for example, where the atmospheric pressure is only about

260 m m H g

, water boils at approximately

71^{\circ} C

. Conversely, if the external pressure on a liquid is greater than

1 a t m

, the vapour pressure necessary for boiling than normal boiling is reached later, and the liquid boils at a temperature greater than the normal boiling point.

Clausius-Clapeyron equation can be written in the following form:

Q. Assertion :The normal boiling point of water is

100^{\circ} C

and standard boiling point of water is

{99.6}^{\circ} C

. Reason: The temperature at which vapour pressure of liquid is equal to the external pressure is called boiling temperature at that pressure.

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