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.