Question

Calculate the enthalpy change, delta H , for the process in which 44.4g of water is converted from liquid at 13.4 degrees celsius to vapor at 25.0 degreescelsius.
For water, delta H = 44.0 kJ/mol at 25.0 degrees Celsius and s = 4.18J/(g*C) for H2O

Answer 1

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Calculate the enthalpy change, Delta H, for the process in which 33.3 g of water is converted from liquid at 4.6 C to vapor at 25.0 C.

For water, H = 44.0 kJ/mol at 25.0 C and s = 4.18J/g C for H2O(l)

ANSWER:

_____Phase change (heat require to go from one "point" to another should be the same, assuming all the heat goes to the change
http://www.lsbu.ac.uk/water/explan4.html - dHvap NOT constant)

at 0C, dHvap = 44060J/mole
at 25C, dHvap = 44000J/mole

"A"___cool water -------------> warm water------------> warm steam
_________4.6C_____________25.0C_______…
_J/g______4.18J/gC * (25.0-4.6)C_+__44000J/mole*1mole/18g = ??J/g

dH = + ??J/g * 33.33g = + ??J (endothermic)

OR

"B"___cool water -------------> cool steam------------> warm steam
_________4.6C_____________4.6C________…
_J/g______44044J/mole*1mole/18g____2.0… * (25.0-4.6)C = ??J/g

Are the J/g the same for "A" and "B"?; they should be!

SOLVE

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