Question

A block of ice weighing 20 lb is taken from the freezer where it was stored at -15"F. How many Btu of heat will be required to convert the ice to water at 200'F?

Answer 1

6700.6 BTU

Explanation:

First you have to warm the block from -15° F to 32°F, the heat to needed to do this is:

`Q_(1)=mc\Delta T=20lb*0.49(BTU)/(lbF) *(32F-(-15F))=460.6BTU`

After you need to melt the ice. The heat you need is:

`Q_(2)=mL=20lb*144(BTU)/(lb)=2880BTU`

Finally, you need to heat the water from 32° F to 200 ° F, and the heat for this is:

`Q_(3)=mc\Delta T=20lb*1(BTU)/(lbF) *(200F-32F)=3360BTU`

`Q=Q_(1)+Q_(2)+Q_(3)=460.6BTU+2880BTU+3360BTU=6700.6BTU`To have the total heat you used you have to su
`Q_(1),Q_(2)` and
`Q_(3)`