Factors Affecting Reaction Rate (Veronica Lopez)

Title: Factors Affecting Reaction Rate

Principle(s) Investigated:

Reaction rate, temperature, concentration, catalyst, surface area and activation energy.

Chemistry

Standards: Chemistry

8.a. Students know the rate of reaction is the decrease in concentration of reactants or the increase in concentration of products with time.

8.b. Students know how reaction rates depend on such factors as concentration, temperature, and pressure.

8.c. Students know the role a catalyst plays in increasing the reaction rate.

8.d. * Students know the definition and role of activation energy in a chemical reaction.

Materials:

Concentration Demo

0.20 M KIO3 solution

0.20 M Na2S2O5

Distilled water

2% starch solution

100 mL graduated cylinder

50 mL graduated cylinder

10 mL graduated cylinder

3- 400 mL beakers

3-250 ml beakers

Temperature Experiment

active dry yeast

apple juice

balloons

cold and hot water (not higher than 40◦C)

hot plate

thermometers

timers

test tubes

balance

Catalyst Experiment

Sodium Thiosulfate

Potassium Iodide

4 possible catalysts: 0.1 M Nickel(II) sulfate, 0.1M Copper (II) sulfate, 0.1M Cobalt (II) chloride, and 0.1M Iron(II) sulfate

10 mL graduated cylinder

50 mL beakers

Timers

Particle Size Experiment

3M HCl

magnesium metal ribbon

50 mL beakers

scissors

timers

Procedure: data table

https://docs.google.com/spreadsheet/ccc?key=0Atsygoht0yF5dFpGdXNRYnllY09IUnAtbUhtMWFEckE#gid=0

Concentration Demonstration

1. Prepare a series of solutions called solution A:

2. Prepare a series of 3 identical solutions called solution B:

3. Pour Solution 1B into Solution 1A. Stir and time the reaction with a stop watch. Record the time from when solutions A and B are mixed until the appearance of the blue color.

4. Pour solution 2B into solution 2A. Record the time. Repeat for solutions 3B and 3A.

Particle Size Experiment

Students will design their own experiment based on the materials present.

Helpful tips:

  1. Cut the magnesium metal into various particle sizes keeping the mass constant.

Catalyst Experiment

Students will design their own experiment based on the materials present.

Helpful tips:

  1. Draw an “x” on a piece of scratch paper and place it underneath the beaker where you will be mixing sodium thiosulfate and Iron (III) nitrate solution.
  2. Mix equal amounts for both solutions.
  3. Record the time from when sodium thiosulfate and Iron nitrate are mixed until you see the “x” when looking down the beaker from the top. This will be your control.
  4. Repeat this experiment but add one drop of a catalyst to the Iron (III) nitrate solution before mixing. Test the rest of the catalysts and record your results.

Temperature Experiment

Students will design their own experiment based on the materials present.

Helpful tips:

  1. Measure no more than 1.5 grams of active dry yeast and mix with no more than 8 mL of apple juice into a large test tube.
  2. Place a balloon over the test tube and dip the test tube into a cold water bath.
  3. Repeat the experiment one more time. This time dip the test tube into a warm water bath. (temperature should be not higher than 40◦C)

Student prior knowledge:

Students need to understand concepts related to bonding. Then they will understand that atoms can come together and form bonds as well as come apart and break existing bonds. Students also need to understand chemical reactions as well as the kinetic molecular theory.

Explanation:

Reaction rate is the time it takes for reactants to form products. Since there are reactants and products in a chemical reaction there are two ways to measure reaction rate. The reaction rate can be measured as the grams or moles of reactants used over time in seconds. The reaction rate can also be measured as the grams or moles of products formed over time in seconds. Before a reaction has occurred the amount of reactants is greater than the amount of products. As time passes the concentration of reactants decreases and the concentration of the products increases because reactants are being used to make the products.

Concentration, temperature, particle size and the presence of a catalyst are factors that affect reaction rate. In the demonstration and student experiments we will investigate how these factors affect the rate of a reaction. In the concentration demonstration, potassium iodate and sodium metabisulfite react to form iodine. The starch solution serves as an indicator of the end of the reaction by forming a deep-blue colored starch–iodine complex. The reaction time can be measured by noting the time until the blue color appears for each trial. When reactants collide they break their existing bonds and form new ones to form the products. As the concentration of the potassium iodate is increasing the chance that reactants will collide to form products increases. This is due to probability. As the concentration decreases the chance that reactants will collide to form products also decreases.

Questions & Answers:

1. How does temperature affect the rate of the reaction?

As the temperature increases the reactants have more kinetic energy and thus more collisions will occur. As collisions increase, the rate of the reaction will also increase. When the temperature decreases the kinetic energy decreases resulting in less collision and a slower reaction rate.

2. How does particle size affect the rate of the reaction?

Particle size has to do with surface area. One big particle has less surface area than a lot of small particles of equal mass. The reaction using small particles will react faster to form the products because there is more surface area exposed to the reaction. Whereas the larger particle has less surface area for the reaction to occur and will consequently slows down the reaction rate.

3. How does the presence of a catalyst affect the rate of the reaction?

A catalyst is a substance that speeds up a reaction by lowering the activation energy, without getting consumed in the reaction. Reactants have a certain energy level and products have another, and in between is the activation energy as shown below. The activation energy is the energy it takes for reactants to form products. Without the use of a catalyst reactions will take longer to occur because the reactants need to overcome more energy before they can for the products.

Applications to Everyday Life:

Bread dough rises more rapidly in warmer temperatures than in colder temperatures. The molecules in the ingredients used to make the bread are moving with more kinetic energy at higher temperatures. The increase in kinetic energy increases the number of collisions as well as the rate of the dough rising. At lower temperatures the molecules of the ingredients have less kinetic energy and therefore less collision will occur between the ingredients causing the bread dough to rise at a slower rate.

Digestion occurs more rapidly with the help of enzymes than without. Enzymes are biological catalysts that speed up reactions in our body. Starch is first broken down by amylase in the mouth. Proteases are enzymes that breakdown proteins in the stomach and small intestine. Lipases are enzymes that break the bonds within lipids in the stomach as well as the small intestine. Without the help of these biological catalysts the reactions rates in the digestive tract would occur at a slower rate.

Higher concentrations of acid in the rain erode marble headstones faster than lower concentrations. At higher concentrations the H3O+ in acid rain have a higher probability of colliding and reacting with the CaCO3 in marble, causing the marble to erode faster.

Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.

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