(THE EFFECT OF TEMPERATURE ON THE RATE OF A REACTION)
The purpose of this demonstration is to show the effect of temperature upon the rate of a reaction.
This demonstration is appropriate for a general or first-year college-prep course. The rate of formation of CO2 (g) from the reaction of Alka-Seltzer tablets with water at different temperatures is easily observed by comparing the rates of inflation of balloons attached to the flasks in which the reactions are carried out.
Approximately 10 minutes.
*See Modifications / Substitutions
Safety goggles must be worn by those doing the demonstration.
In place of Erlenmeyer flasks, 10-12 oz. soda bottles may be used.
- Alka-Seltzer tablets
- tap water - hot, room temperature, and cold
- balloons (previously blown up to stretch them)
- 125-mL Erlenmeyer flasks*
- chemical scoops, spatulas or spoons
Solutions may be flushed down the drain with water.
Bicarbonate and hydrogen ions, produced when Alka-Seltzer dissolves in water, react according to the following equation:
- Ask students to help with the demonstration; it will require at least one student per flask.
- Fill one flask about half way with hot tap water. Add an equal volume of room temperature tap water to the second flask and an equal volume of cold tap water to the third.
- Practice putting the balloon over the mouth of the flask.
- Break three Alka-Seltzer tablets into comparable size pieces.
- Add one broken tablet to each flask.
- Immediately put a balloon over the mouth of each flask.
- Note the rate of balloon inflation.
- Compare the sizes of the inflated balloons when the reactions are finished to demonstrate that only the rate of reaction is affected, not the final amount of product.
HCO3-(aq) + H+(aq) ----> H2O (l) + CO2 (g)
Increasing the temperature increases the rate of reaction because at the higher temperature, a greater percentage of ions in the sample have energy greater than the required activation energy for the reaction. The observed rate of inflation of the balloons, which is shown to be related to the temperature at which the reaction takes place, is a measure of the rate of formation of carbon dioxide gas.
Check balloons before doing the demonstration to be sure that they will inflate with the pressure generated.
Smoot, Robert, Chemistry: A Modern Course, Merrill Publishing Co., Columbus, OH, 1983. This work desribes a similar demonstration.
Submitted by Patti Ruff, Bill Vitori, Irene Walsh, Doug Wilbur, and Joe Don Wilkins
Woodrow Wilson Leadership Program in Chemistry
The Woodrow Wilson National Fellowship Foundation
CN 5281, Princeton NJ 08543-5281