Energy and Enthalpy Homework Problem Set

1. An electric stove has a 1200 watt heating element. If it takes 5 minutes for a teakettle to come to a boil, how much energy (in joules) is required?

2. A piece of titanium metal (mass 452.398 g) is placed in boiling water (100.00 °C). After 20 minutes it is removed from the boiling water and placed in a 1.000 liter container of water at 20.00 °C. The temperature of the water increases to 24.28 °C. What is the specific heat of titanium? How does this compare to the value given in the CRC Handbook of Chemistry and Physics?

   Next the same piece of titanium is heated in an acetylene flame (like that used for welding) to an unknown temperature. When the piece of titanium is placed in a 10.000 liter container of water at 20.00 °C the final temperature is now 30.72 °C. What is the tempearature of the flame (assuming that the piece of titanium was at equilibrium)? At what temperature does titanium melt?

3. Calculate the energy required to heat a 155.4 g ice cube that starts in a freezer at -100.0 °C (VERY COLD):
   1. Heat from the freezer to ice at 0.0 °C.
   2. Heat from ice at 0.0 °C to liquid at 0.0°C.
   3. Heat from liquid at 0.0 °C to liquid at 100.0 °C.
   4. Heat from liquid at 100.0 °C to gas at 100.0 °C.
   5. Heat from gas at 100.0 °C to gas at 200.0 °C.
   6. Heat from ice at -100.0 °C to gas at 200.0 °C

4. Balance the following reactions, calculate [delta]H_rxn, calculate the energy released (or required) for the combustion of 10.500 grams of fuel (H₂, CH₄ (methane), or C₄H₁₀ (butane)) in each reaction, and compare the energetics for the reactions (which is the best fuel).
   1. H₂ (g) + O₂ (g) --> H₂O (g)
   2. CH₄ (g) + O₂ (g) --> CO (g) + H₂O (g)
   3. CH₄ (g) + O₂ (g) --> CO₂ (g) + H₂O (g)
   4. C₄H₁₀ (g) + O₂ (g) --> CO₂ (g) + H₂O (g)

Scott Van Bramer
Department of Chemistry
Widener University
Chester, PA 19013

© copyright 1996, S.E. Van Bramer
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Last Updated: Saturday, May 18, 1996