One kilogram of ice at 0C is mixed with one kilogram of water at 80C. The final temperature of the mixture is (Take specific heat of water = 4200J kg⁻¹K⁻¹, Latent heat of ice = 336kJ kg⁻¹)
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Always compare heat released and heat absorbed when phase change is involved.
Step 1: Heat released by hot water cooling to 0C:
Q = mcΔ T = 1×4200×80 = 336000J
Step 2: Heat required to melt ice:
Q = mL = 1×336000 = 336000J
Step 3: Heat is just sufficient to melt ice; remaining heat raises temperature of 2 kg water to 40C.