(a) The high heat of vaporization of water is what makes steam dangerous. Determ

Question

(a) The high heat of vaporization of water is what makes steam dangerous. Determine the amount of boiling water if spilled over your skin surface could produce the same amount of heat exposed by 5 gm of steam at the same surface. Assume the skin raises its surface temperature to 35 oC at thermal equilibrium in both cases. Show your detail calculations. (Lice=80 Cal/gm; Lsteam=538 Cal/gm; Cwater=1 Cal/gm-K)

(b) Assume a 1 gm of frozen ice at 0oC is mixed with 5 gm of culture mammalian cells at 25oC in an isolated system during an in-vitro experimentation. Subsequently 1 gm of steam was further exposed to the above mixture in the experiment. Determine the total mass and final temperature of the product of the mixture at thermodynamic equilibrium taking approximation of the cytoplasmic cell composition to water.

Explanation / Answer

When steam is exposed, steam first condenses at 100 deg.c and then losses sensible heat from 100 deg.c to 35 deg.c. In case of boiling water which is at 100 deg.c, it loses only sensible heat from 100 deg.c to 35 deg.c

Hence heat lost by steam includes latent heat + sensible heat= 5*538+5*1*35

Heat lost by boiling water= mass*1*35= 5*538+5*35

mass sof boiling water= 81.85 gm

b) First forzer ice melta and this heat is = 1*80

further water also reaches a equilibrium temperature T which is given by

=1*1*(T-0)

Ttoal heat to be added = 80+T

This comes from 5gm of culture which has to supply heat which is equal to =5*1*(25-T)

hence 80+T= 5*1*25- 5T

6T= 125-80= 45

T= 45/6= 7.5 deg.c

hence both frozen ice and culture will be reaching a temperature of 7.5 deg.c

Noe when steam is exposed, steam gets condensed and this heat= 538*1= 538 cal

and steam losses sensible heat which is given by = 1*1*(100-T)

total herat to be removed from stream= 538+(100-T)

this heat is taken by the total of ice and culture of 1+5=6 gm which is at 7.5 deg.c

so sensible heat gained by the mixture = 6*1*(T-7.5)= 638-T

6T-45= 638-T

7T= 638+45= 683

T= 683/7=97.57 deg.c

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