2001 Chemathon - Avogadro's Tiebreaker
(tied to the poster theme "Chemistry in the Arts")
(The team was given the question sheet, a periodic table with atomic
weights, and scrap paper.)
Tiebreaker question - first-year teams:
An 80-pound ice sculpture is the centerpiece of a table under a tent
during an outdoor party. It was kept in a 0 Celsius degree freezer
until 12:00 noon when the party began. The tent temperature was 80
degrees Fahrenheit.
Specific heat of water = 4.184 J / g K
Hvap(H2O) = 2260 J / g
Hfus(H2O) = 333 J / g
1 kcal = 4184 J
A. How much energy is necessary to completely melt the sculpture?
B. How much energy is required for the melted ice to evaporate?
C. After reaching 70 degrees Fahrenheit, how much energ must be removed
to refreeze the melted ice?
D. At 3:00 p.m., how much of the ice sculpture has melted if 80 degrees
Fahrenheit was equivalent to 126.5 W?
Tiebreaker question - second-year teams:
A. Carbon-14 decays as follows. Calculate the first-order decay
constant.
| Time |
Mass |
| 0 |
28.165 g |
| 73 yrs |
27.918 g |
| 151 yrs |
27.657 g |
| 299 yrs |
27.167 g |
| 350 yrs |
27 g |
B. Calculate the half-life of the reaction.
C. An oil painting supposed to be painted by Rembrandt (1606-1669 AD)
is checked by 14C dating in 1993. The 14C (t1/2
= A) content is 0.961 times that in a living plant. Could
Rembrandt have done the painting? Show work.
D. Suppose that the 14C / 12C ratio in plants
300 years ago was 10% higher than today. Could Rembrandt have painted
the painting under these conditions? Show work.