Heat of Vaporization H_v of Water (Demonstration Lab)
Obj: Measure the H_v of water
Materials: See the diagram below.

Sketch by Ted Andersen, retired Physics Teacher at Brockport High, a teacher’s teacher!

Methods
1. Mass the insulated cup, then the cup with water; record the starting temperature (0.1^oC).
2. Boil the water, bubbling "live" steam (100^oC) into the insulated cup.
3. Record the change in temperature of the water ΔT.
4. Mass the cup with water again to determine the mass of the condensed steam.

Analysis
1. Calculate H_v using the equation for heat loss/heat gain (Q_lost) = Q_gained)
                    m_w c ΔT = m_s H_v + m_s c ΔT where m_s is the mass of the steam only
                    (water) (steam) (steam)

2. Determine the % error. What are some sources of error?
3. Define H_v.
4. Why was it desirable to use steam at 100⁰C?
5. Why did we start with water at approximately 10⁰C?
6. Describe some practical applications of water’s high H_v.

Data Table
mass of cup_________ kg
mass of cup + water __________ kg
mass of water ______________ kg
temperature (cool) __________ ^oC
temperature (hot) ___________ ^oC
Final temperature of water ______________ ^oC
Temperature changes: Condensate ______________^oC, Cold water______________^oC
mass of cup + water + condensate _____________
mass of condensate (steam m_s) ___________

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