+
Reaction Rates !
February 11 and 12, 2013
Boon Chemistry
+
Catalyst
You will have about 2 minutes to answer on your own. Then you
will have about 1 minute to share.
(1) Give two examples of units
that could be used to measure a
car’s rate of motion.
(2) What can you do to slow the
rate at which milk spoils?
+

Objective
• I can define reaction rate and investigate factors that affect reaction
rate.

Agenda




Catalyst
Notes: Reaction Rate
Demonstrations & Mini-Lab: Factors affecting reaction rate
Practice: Reaction Rate Foldable
+
What is Reaction Rate?
Rate = change
over time

Reaction rate is the rate at which a chemical reaction takes place.

It is measured by the rate of production of product or
disappearance of reactant.
+
What is reaction rate?

A chemical reaction does not have one specific reaction rate.
Rather, reaction rate is affected by many different conditions
like concentration, temperature, surface area and pressure.

Usually, the rate decreases gradually as the reaction
continues. The rate is zero when the reaction is complete.
Video: Reaction Rates vs. Dating -http://www.youtube.com/watch?v=OttRV5ykP7A
Discussion Question: What analogy does the video use to explain the
factors that affect reaction rates? What factors affect reaction rates? Can
you think of your own analogy?
+
Affect of Surface Area on Reaction
rate.

The investigation shows the relationship between surface area and
reaction rate.

We have two beakers with 50 mL of vinegar. In beaker 1, we will put a
whole antacid tablet. In beaker 2 we will put a ground up antacid
tablet.

Hypothesis: How do you think the difference in surface area will affect
reaction rate?

Record your observations in the space on your handout.

Conclusion: As surface are increases, rate increases. As surface area
decreases, rate decreases.
+
Affect of Reactant Concentration
on Reaction Rate

The demonstration shows the relationship between reactant
concentration and reaction rate.

The video shows the reaction of Hydrochloric acid and calcium
carbonate (marble chips)

Each successive reaction uses a lower concentration of hydrochloric
acid.

Record your observations in the space provided.

How does changing the concentration of reactants affect the rate of
reaction?
+
Demonstration



The Chemical Reaction:
HCl + CaCO3 
CO2 + H2O + CaCl2
(a) Label the reactants and products. (b) What reactant
concentration will be varied? (c) What gas is produced?
+
Demonstration: Concentration and
reaction rate

Explanation: In order for the reaction to take place, the
reactant molecules need to come in contact with each other.
The more HCl molecules there are dissolved in the water, the
greater the chances that these molecules will collide with the
marble chips.

Conclusion: As reactant concentration increases, rate
increases. As reactant concentration decreases, rate
decreases.
+
Investigation: Affect of
Temperature on Reaction Rate.

The investigation shows the relationship between
temperature and reaction rate.
+
Introduction to
Chemiluminescence

In nature, an example of chemiluminescence would be the
firefly, which very efficiently creates light through a chemical
reaction. Through industrial chemistry we have also created a
similar form of emission; however, it is still not as efficient as
a firefly. The most common reaction used in novelty toys like
glowsticks is that of Cyalume with hydrogen peroxide.
Peroxides give off a lot of energy in chemical reactions, and
therefore would be perfect for such a precise and efficient
reaction.
+
Introduction to
Chemiluminescence

The chemical reaction:

cyalume + H2O2 + dye → trichlorophenol + 2CO2 + dye[♦]
In the equation above the diamond [♦]
represents the excited stage during
which the chemicals give off light. In
this investigation, we will study the affect
of temperature on the rate of the
chemiluminescence reaction.
+
Investigation

Summary of Procedure: (1) Submerge one light stick in a
bath of cold water (about 10°C). (2) Submerge a second light
stick in a bath of hot water (about 50°C). (3) Allow each light
stick to reach the same temperature as its bath. (4) Remove
the light sticks, and activate them. (5) In a dark corner of the
room, observe and compare the light intensities of the two
sticks. (6) Record your observations.


Hypothesis: How do you think the temperature of the glow
stick will affect the reaction rate?
+
Explanation and Conclusion

Explanation: As temperature increases, the proportion of
molecules with enough energy to make a collision lead to a
chemical reaction increases. The affect is not only about the
increased number of collisions, but the increased energy of
the collisions. Decreasing the temperature as the opposite
effect.

Conclusion: As temperature increases, rate increases. As
temperature decreases, rate decreases_.
+
Reaction Rates Foldable

Fold and cut the foldable worksheet so that it has “doors.”

Use your notes to fill in as much information as you can in the
foldable.

When you are done, go to edmodo.com and click on the
brainrush game to check your understanding.
+
Reaction Rate Foldable

Fold the worksheet in half the long way so that it opens like a
book. The question: “What is reaction rate and how is it
measured?” should be at the top of the front cover.

Cut along the lines between the questions to make “doors” for
your foldable.

Use your notes to fill in the blanks on the inside of the foldable.

When your foldable is complete, use it to practice the new
vocabulary.

Additional practice: Read pp. 575-585 problems pp. 585 #1-13.

If you need help working on your phase change diagram project,
you may work on that now. Please raise your hand if you have
questions.
+
Homework

Read pp. 586-595. Pay particular attention to information
about activation energy and catalysts.

Problems pp. 595 #3, 4, 5, 9, 11, 14

Phase Change Diagram Project Due Wednesday March 12.