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Properties of Matter question

2019 · Shift 1 · Q52
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Properties of Matter question

2019 · Shift 1 · Q52

JEE AdvancedPhysicsProperties of MatterNumerical+3 / −1
A liquid at 30 ∘^\circ∘ C is poured very slowly into a Calorimeter that is at temperature of 110 ∘^\circ∘ C. The boiling temperature of the liquid is 80 ∘^\circ∘ 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 ∘^\circ∘ C. The ratio of the latent heat of the liquid to its specific heat will be ........... ∘^\circ∘ C. [Neglect the heat exchange with surrounding]
Numerical answer
View written solutionFree

Correct answer: 270

  1. Let the calorimeter heat capacity be CCC (in cal/^ ircC), the liquid specific heat be sss (in cal g^{-1} ircC−1^{-1}−1), and latent heat be LLL (in cal g−1^{-1}−1).

  2. 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: Q1=5s(80−30)+5L=5(50s+L)Q_1 = 5s(80-30) + 5L = 5(50s + L)Q1​=5s(80−30)+5L=5(50s+L)

This heat comes from the calorimeter cooling from 110^ ircC to 80^ ircC: Q1=C(110−80)=30CQ_1 = C(110-80)=30CQ1​=C(110−80)=30C

Hence, 30C=5(50s+L)30C = 5(50s+L)30C=5(50s+L) 6C=50s+L(1)6C = 50s + L \quad \text{(1)}6C=50s+L(1)

  1. 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: Q2=C(80−50)=30CQ_2 = C(80-50)=30CQ2​=C(80−50)=30C

Heat gained by 80 g liquid: Q2=80s(50−30)=1600sQ_2 = 80s(50-30)=1600sQ2​=80s(50−30)=1600s

Thus, 30C=1600s30C = 1600s30C=1600s C=1600s30=1603sC = \frac{1600s}{30} = \frac{160}{3}sC=301600s​=3160​s

  1. Substitute into equation (1)

From (1): 6C=50s+L6C = 50s + L6C=50s+L 6(1603s)=50s+L6\left(\frac{160}{3}s\right)=50s+L6(3160​s)=50s+L 320s=50s+L320s = 50s + L320s=50s+L L=270sL = 270sL=270s

Therefore, \frac{L}{s} = 270^ irc\text{C}

  1. Final Answer

The required ratio is: 270\boxed{270}270​

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