Quantitative problems
Be sure to show work and label quantities. Show how units cancel.
Useful constants
334 J/g Heat of fusion (Hf) (melting or freezing)
2260 J/g Heat of vaporization (Hv) (evaporating or condensing)
2.10 J/g˚C Heat capacity (c) of solid water
4.18 J/g˚C Heat capacity (c) of liquid water

15. (4) While you were “sweating” your chemistry test, water vapor evaporates from your body, absorbing 125 kJ of energy. (Assume no temperature change). What mass of water evaporates?

Question

Quantitative problems
	Be sure to show work and label quantities.  Show how units cancel.
Useful constants
334 J/g 		Heat of fusion (Hf)  (melting or freezing)	
2260 J/g		Heat of vaporization (Hv) (evaporating or condensing) 
2.10 J/g˚C	Heat capacity (c) of solid water
4.18 J/g˚C	Heat capacity (c) of liquid water

15. (4) While you were “sweating” your chemistry test, water vapor evaporates from your body, absorbing 125 kJ of energy. (Assume no temperature change).  What mass of water evaporates?

anonymous · Answer

i know that this is more of a chemistry problem, but please if u know it, help me! :)

joannablackwelder · Answer

Since this is just a phase change problem and no temp change, the appropriate constant is the heat of vaporization.

joannablackwelder · Answer

Do you have any ideas on how to use it?

anonymous · Answer

no

joannablackwelder · Answer

Well, the way I would do this is to start with 125 kJ of energy. I know that each gram of water evaporated absorbs 2260 J of energy.

joannablackwelder · Answer

So, if we use the 1 gram evaporated = 2260 J as a fraction to cancel out the units we don't want but not change the value, we can find the mass.

joannablackwelder · Answer

125 kJ * (1000 J/1 kJ) = 125,000 J

joannablackwelder · Answer

And 125,000 kJ * (1 g/2260J) = ?