Name _________________________
Particle Size (Surface Area), temperature and Rate of Reaction
Ideas
The rate of a chemical reaction is affected by the physical size of the reactants and by temperature.
Decreasing the size of the particles which make up a given weight will increase the number of particles
represented by the same weight. Smaller particle size results in an increase in the rate
of reaction. Similarly, warmer water (or conditions) will speed up a reaction.
My predictions:
1.) The powder will react _______ times faster than the whole tablet.
2.) Using hot water out of the tap, the rate of reaction will be _________ times faster
than with cold water.
Materials
Note: All experiments should be done using original formula effervescent Alka-Seltzer.

2 Clear beakers

3 Alka-Seltzer tablets

Mortar and pestle (pencil and sheet of paper)

Stopwatch (on iPad)
Procedure
I. Particle Size
A. Whole Tablet
1. Fill a clear glass beaker with exactly 100 ml of cold
water.
2. Drop 1 whole Alka-Seltzer tablet into the water.
Measure and record the time to dissolve.
B. Powdered Tablet
1. Place 1 Alka-Seltzer tablet on to a sheet of paper and grind to a fine powder.
2. Transfer powder into a clear cup. (Note: It's important to have the powder in the cup before
adding water.)
3. Add 100 ml of cold water to the glass. Measure and record the time to dissolve.
Name _________________________
Observations
Particle Size Time for reaction to be completed
Whole Tablet _________ Seconds
Powder _________Seconds
Summary
a) As particle size decreases, the rate of reaction _______________.
b) The rate of reaction for the powder was ___________ times faster than for the whole tablet.
Questions
1. As particle size decreases, the total surface area of a reactant ________________. As a result,
the probability of interactions between atoms/ions ________________, and the rate of reaction
___________________.
2. Particle size appears to have _______________ (less or more) of an effect on the rate of
reaction than temperature.
II. Water Temperature
A. Hot Water
1. Run water from the hot tap until it is as hot as possible. Fill a clear glass beaker with exactly
100ml of hot water.
2. Remove 1 Alka-Seltzer tablet from its package. Drop it into water. Measure the time required for
tablet to fully dissolve. Be prepared to start and stop on time. The reaction may take less than
15 seconds. Record the time.
B. Cold Water
1. Use your data from the whole, cold tablet in part one, when comparing with the hot water
tablet you just conducted.
Observations
Time for Reaction to be Completed
Hot Tap
_____ Seconds
Cold Water
_____ Seconds
Name _________________________
Summary
As the temperature increases, the rate of reaction _____________________________.
Questions
1. Using hot tap water, the rate was ______ times faster than at 0 degrees C.
III. My thoughts
Explain why smaller particle size allows for a faster reaction.
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Explain why warmer temperature allows for a faster reaction.
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