Question

The temperature of 50g of water has to be risen from 15°C to 85°C by using steam at 120°C. What is the amount of steam, in gms, required for the same? Sw= 1cal/ g°C, Lvap = 540cal/g, Ssteam =0.48cal/g°C.

(a) 6.29g

(b) 8.34g

(c) 7.22g

(d) 6.19g

This question was addressed to me during an interview for a job.

The origin of the question is Thermal Properties of Matter topic in section Thermal Properties of Matter of Physics – Class 11

Answer 1

The correct choice is (d) 6.19g

To explain: Heat lost by steam = Heat gained by water. Let ‘m’ be the mass of steam required.

∴ mSsteam (120-100) + mLvap + mSw (100-85) = 50Sw (85-15)                                                                                                                                                                             The only variable is ‘m’.

On calculating it from the above equation, we get:

m = 6.19g.