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Reaction Powered Car
CBEE 101 Fall 2009Hailey DeMarre, Michael Lougee, Peter Shoaf
Dr. Skip Rochefort
The Alka-Seltzer Reaction• Reactants: Citric Acid (aq) and Sodium Bicarbonate (aq)• Products: Water (L), Carbon Dioxide (g), and Sodium Citrate (aq)• Balanced Equation:
C6H8O7(aq)+3NaHCO3(aq)→3H2O(l)+3CO2(g)+Na3C6H5O7(aq) • Solving for the amount of reactants to use:
Ideal Gas Law: P=nrT/v => Pv/rT = nThe pressure was supposed to be about 5 atm; P=5 atm.The gas constant is always the same; r=0.08205 atm-L/mol-K.The outside temperature was about 7 degrees C, or 280K; T=280K.The volume of the Propel bottle is 700 mL filled with 200 mL of water; v=0.5L.
EXAMPLE CALCULATION:n = (5 atm)(0.5 L)/[(0.08205 atm-L/mol-K)(280 K)]
n = 0.1088 mol CO2
(0.1088 mol CO2)(1 mol NaHCO3/1 mol CO2)(0.845 g NaHCO3/1 mol NaHCO3)=9.139 g NaHCO3
(0.1088 mol CO2)(1 mol C6H8O7/3 mol CO2)(0.136 g C6H8O7/1 mol C6H8O7)=4.930 g C6H8O7
These calculations show how much of each reactant should be used in order to obtain enough pressure to PROPEL the car.
Car Design
• The design is very simple, optimizing weight.• Only 4 wheels, axels, middle support, and the
bottle, held on by low weight hair ties.
Testing Results
Trial Sodium Bicarbonate (g) Citric Acid (g) Water (mL) Distance (ft)
1 12.033 8.951 200 0
2 12.081 8.894 200 0
3 13.576 8.741 100 14
4 11.402 8.771 75 0
5 11.465 9.183 75 0
6 14.112 9.525 100 25
7 14.466 9.740 100 3
8 14.448 9.879 100 35
9 14.493 9.452 100 42
10 14.201 9.260 80 5
Trials 8, 9, and 10 are the official testing trials. Trials 1 through 7 were done without instructor supervision
Conclusions
• Performance:– Distance varied a lot.
• Mostly due to changes in the way the reactants were added together and amount of water used.
– The amount of reactants used was not conjoint with the calculations for 5 atm.
• We did not wait long enough for all of the reactants to be used because the bottle was leaking.
• Some of the reactant amounts that were used were calculated using the total volume of the bottle, not considering the volume of water.
Redesign:– Would use the same simple and lightweight design.– Maintain consistency of amount of reactants used.– Use a container that didn’t leak under pressure as easily.– Wait for the reactants to fully react before releasing pressure.