Ice at `0^@C` is added to 200 g of water initially at `70^@C` in a vacuum flask. When 50 g of ice has been added and has all melted the temperature of the flask and contents is `40^@C`. When a further 80 g of ice has been added and has all melted the temperature of the whole becomes `10^@C`. Find the latent heat of fusion of ice.A. `80 cal//g`B. `90 cal//g`C. `70 cal//g`D. `540 cal//g`

Ice at `0^@C` is added to 200 g of water initially at `70^@C` in a vac

1.	Ice at `0^@C` is added to 200 g of water initially at `70^@C` in a vacuum flask. When 50 g of ice has been added and has all melted the temperature of the flask and contents is `40^@C`. When a further 80 g of ice has been added and has all melted the temperature of the whole becomes `10^@C`. Find the latent heat of fusion of ice.A. `80 cal//g`B. `90 cal//g`C. `70 cal//g`D. `540 cal//g`
Answer» Correct Answer - B According to principle of calorimetry `ML_f+MsDeltaT=(msDeltaT)_(water)+(msDeltaT)_(flask)` `50L_F+50xx1xx(40-0)` `200xx1xx(70-40)+W(70-40)` `50L_F+2000=(200+W)30` `5L_F=400+3W` .(i) Now the system contains `(200+50)` g of water at `40^@C`, so when further 80 g of ice is added `80L_F+80xx1xx(10-0)` `=250xx1xx(40-10)+W(40-10)` `80L_F=670+3W` .(ii) solving Eqs. (i) and (ii), `L_F=90(cal)/(g)` and `W=(50)/(3)g`

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