Reaction Rates

    Kids, do you think that temperature will have an affect on how fast or slow a reaction might take place?  In order for a chemical reaction to occur, the molecules, which are REACTANTS, must physically come into contact with one another. Anything that increases the frequency of these encounters will increase the rate at which PRODUCTS are formed. Your hypothesis can be that the rate of a chemical reaction will be increased by raising the temperature of reactants.

    Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

    You will need: 6 clear cups, a measuring cup, a thermometer (-20° C to 110° C), 3 original formula effervescent Alka-Seltzer® tablets, a stopwatch, a mortar and pestle, a source of hot water, ice cubes, and graph paper.

    Procedure—  Run water from the hot tap until it is as hot as possible. Fill a clear glass with exactly 8 oz. of hot water. Use the thermometer to take the temperature and record it on a data sheet. Drop 1 Alka-Seltzer® tablet into water. Measure the time required for the tablet to fully dissolve. Be prepared to start and stop on time. The reaction will take less than 15 seconds. Record the time. Repeat this experiment using room temperature water.

    For the cold water test, the procedure is a little different. Fill a clear glass with 4 oz. of water and add enough ice to adjust the level to 8 oz. Stir the ice water for about 15 seconds so the temperature will come to equilibrium. Use the thermometer to take the temperature and record it on your data sheet. (Leave the ice cubes in the water!) Drop 1 Alka-Seltzer tablet into the water. Measure and record the time required for the reaction to be completed.

    Analysis—  Graph your data points (water temperature vs. time to fully dissolve) to show the effect of temperature on Rate of Reaction.

    So now can you answer this question? As the temperature increases, the rate of reaction increases, decreases, or stays the same? How about these more advanced questions?

    1. At a temperature of 10 degrees C, it would take ______ seconds for 1 Alka-Seltzer tablet to react with 8 oz. of water.
    2. If the temperature is doubled from 20 degrees C to 40 degrees C, the time for the rate of reaction ______by approximately _______.
    3. Using hot tap water, the rate was ______ times faster than at 0 degrees C.


    Kathleen Carrado Gregar, PhD, Argonne National Labs 
    [email protected]
    April 2007