Question

4 gms of steam at 100⁰C is added to 20 gms of water at 46⁰C in a container to negligible mass. Assuming no heat is lost to surrounding, the mass of water in container at thermal equilibrium is. Latent heat of vaporisation = 540 cal/gm. Specific heat of water = 1 cal/gm⁰C –

• A. 18 gm
• B. 20 gm
• C. 22 gm
• D. 24 gm

Answer 1

Answer: (C)

22 gm

Answer 2

Heat released by steam in conversion to water at 100⁰C is Q₁ = mL = 4 × 540 = 2160 cal. Heat required to raise temperature

of water from 46ŗC + 100⁰C is Q₂ = mS Dq = 20 × 1 × 54 = 1080 J.Q₁ > Q₂ and $\frac{Q_{1}}{Q_{2}}$ = 2

Hence all steam is not converted to water only half steam shall be converted to water.

\ Final mass of water 20 + 2 = 22 gm.