THE EFFECT OF TEMPERATURE ON THE RATE OF A REACTION

PURPOSE

The purpose of this demonstration is to show the effect of temperature on the rate of a chemical reaction.

This demonstration is appropriate for a general or first-year, college prep class. Students observe the amount of time it requires for the reaction of an Alka-Seltzer tablet in water of three different temperatures.

TIME REQUIRED

10-15 minutes.

MATERIALS

Chemicals:: Alka-Seltzer tablets (should be fresh); water - hot, room temperature, and cold
Equipment:: clock which can measure seconds; 250-mL beakers*

*See Modifications / Substitutions

MODIFICATIONS/SUBSTITUTIONS

Clear plastic glasses may be substituted for the beakers.

PROCEDURE

Fill the beakers with equal volumes of water at three different temperatures. Use cold water from a refrigerated water fountain or the cold water tap (if significantly below room temperature), room temperature water, and water from the hot water tap. Label the beakers with the appropriate temperature.
Add an Alka-Seltzer tablet to one of the glasses. Record the amount of time it takes for the violent evolution of bubbles to cease.
Repeat for the other two temperatures of water.

DISPOSAL

Pour solutions down the drain.

DISCUSSION

Alka-Seltzer tablets contain a mixture of solids that produce bicarbonate and hydrogen ions when they dissolve in water. The following is the net equation for the reaction that occurs.

HCO₃^-_(aq) + H⁺_(aq) ----> H₂O_(l) + CO_{2 (g)}

Increasing the temperature of the water increases the rate of the reaction because at higher temperatures a greater number of collisions involve sufficient energy to overcome the activation energy barrier for the reaction.

REFERENCES

Summerlin L.R. and Ealy, J.L., Jr.,Chemical Demonstrations - A Sourcebook for Teachers, American Chemical Society, Washington, DC, 1985, p. 70. Describes a similar demonstration using two temperatures of water and adding the Alka-Seltzer tablets simultaneously without timing.

Submitted by Patti Ruff, Bill Vitori, Irene Walsh, Doug Wilbur, and Joe Don Wilkins

Woodrow Wilson Leadership Program in Chemistry

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The Woodrow Wilson National Fellowship Foundation

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