Biology/Chemistry

 

Chemical Reaction Rates

 

Ken Schug

Illinois Institute of Technology

1466 East Park Place

3101 South Dearborn

CHICAGO IL 60637

CHICAGO IL 60616

(773) 567-3042

(312) 567-3438

 

Objective(s):

 

To learn phenomenologically some of the factors which affect the rates of chemical reactions.

 

Materials:

Per Experiment A: 50 mL (circa 2 ounces) of 3% hydrogen peroxide, one tablespoon of activated dry yeast, two quart kitchen storage bags (with ties), small glass jar with cap, matches, fireproof surface, and a cigarette or wood splint.

Per experiment B: two tablespoons household flour, fireproof surface (e.g. empty food can), funnel with three foot rubber or plastic tube attached, matches (preferably long “fireplace” type)

 

Strategy:

  1. Fill bag 1 with air and tie off. To bag 2 add yeast and capped jar containing hydrogen peroxide, force out most of the air, and tie off, then remove cap from bottle and allow contents to mix. Bag will slowly inflate as an enzyme in the yeast acts as a CATALYST for the decomposition of hydrogen peroxide into water and oxygen gas. Place bags on fireproof surface and touch each with glowing cigarette or splint. With bag 1, a small hole will be formed when the plastic melts but bag 2 will burst into flame, demonstrating the effect of reactant CONCENTRATION on reaction rates. (Bag 1 contains 20% oxygen by volume and bag 2 nearly 100%. Can be related to signs in hospitals where oxygen is being administered to avoid sources of ignition.  [P.S. Using two yeast/ peroxide bags, cooling one with ice and warming the other –not too hot unless you also want to show deactivation of enzymes – might be a way to demonstrate the effect of TEMPERATURE on reaction rates from the rates of inflation of the bags. Author hasn’t tried this yet]
  2. Place tablespoon of flour on inverted can and try to ignite with a match; will get some charring but not extended flame. Place another tablespoon of flour in wide end of funnel, lift above your head, and hold a lighted match about a foot above the funnel while blowing into tube. With some practice, a large flame of burning flour will form (more impressive if room is darkened first) showing the effect of SURFACE AREA on reactions involving solids or gases. Can be related to explosions in grain elevators, using twigs to start campfires.

 

Performance Assessment:

Describe other situations involving the above variables and ask students to predict effect on the reaction rate. Extra credit is given for students coming up with their own examples.

 

Conclusions:

This experiment provides a phenomenological way to demonstrate factors that affect the rates of chemical reaction with readily available materials.