JEE AdvancedPhysicsProperties of MatterNumerical+3 / −1
A liquid at 30 C is poured very slowly into a Calorimeter that is at temperature of 110 C. The boiling temperature of the liquid is 80 C. It is found that the first 5 gm of the liquid completely evaporates. After pouring another 80 gm of the liquid the equilibrium temperature is found to be 50 C. The ratio of the latent heat of the liquid to its specific heat will be ........... C. [Neglect the heat exchange with surrounding]
Numerical answer
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Correct answer: 270
-
Let the calorimeter heat capacity be (in cal/^ircC), the liquid specific heat be (in cal g^{-1}ircC), and latent heat be (in cal g).
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First 5 g of liquid completely evaporates
- Initial temperature of calorimeter = 110^ircC
- Liquid is poured at 30^ircC
- Since it evaporates, it must first be heated from 30^ircC to its boiling point 80^ircC, then vaporized.
So, heat absorbed by 5 g liquid:
This heat comes from the calorimeter cooling from 110^ircC to 80^ircC:
Hence,
- Then another 80 g of liquid is poured
At this stage, the calorimeter is at 80^ircC. The new 80 g liquid is at 30^ircC, and final equilibrium temperature is 50^ircC.
So, heat lost by calorimeter:
Heat gained by 80 g liquid:
Thus,
- Substitute into equation (1)
From (1):
Therefore, \frac{L}{s} = 270^irc\text{C}
- Final Answer
The required ratio is:
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