1. Honors Chemistry Reaction Rates
Chapter 16 - Kinetics
Honors Chemistry
Reaction Rates

2. What is the reaction rate?
Kinetics - The branch of chemistry that is concerned with the rates of change in the concentration of reactants in a chemical reaction.
The reaction rate is a measure of the change in the concentration of reactants or products over time in a chemical reaction (mol/L·s)
Reactions can happen very quickly or extremely slow.
Examples:
fast and furious chemical rxn slower rxn rate millions of years rxn rate

3. Expressing Reaction Rates
Fast and slow helps us to visualize the speed of chemical reactions, but chemists, doctors and engineers need to be more specific about how fast reactions occur. For example, a knowledge of the speed at which radioactive tracking devices break down in the human body enables doctors to take x-rays to diagnose diseases.

4. Expressing Reaction Rates
In medicine, specific isotopes are used to observe the condition of specific organs. A common procedure is the injection of iodine-131 for the observation of the thyroid gland. A healthy thyroid will accumulate any iodine entering the body. Because the body cannot distinguish between stable iodine and its radioactive isotope, iodine-131 will also be accumulated. When a physician scans the patient, if iodine-131 is present in the thyroid, the gland is working properly. However, if the trace element has not collected in the thyroid, the physician knows the gland is failing.
Thyroid gland
Showing cancer

5. Expressing Reaction Rates
Related technology is often used in industrial settings. Using trace elements, engineers can follow the path of a coolant or lubricant throughout a system. It is also used to identify inclusions, cracks, areas of porosity, and other flaws. When used in test situations, radioisotopes can help to detect areas of abnormal wear and corrosion.

6. Rate of change
At what rate is this car traveling?
If the rate is 50, what is this in the metric system?
How is rate of a reaction expressed?
What is happening to the reactants and products over time?
Reaction Rate and units
Definition:
Units:

7. Why is my answer negative?
Reaction Rates are determined experimentally:
CO + NO2  CO2 + NO
Note: negative reaction rate values indicate that the concentration of a compound decreases as the reaction proceeds. When the rate is measured by consumption of a reactant, a negative sign is applied to the calculation to get a positive reaction rate.
Average Rate =
Example:
If the concentration of NO is 0.000M at time t1=0.00 s and 0.010M two seconds after the reaction begins, the following calculation gives the average rate of the reaction expressed as moles of NO produced per liter per second.
Answer:
Why is my answer negative?

8. Reaction Rate Calculations
The speed at which a process works is measured against time. For example, a sprinter moves in meters per second, the speed of a car in miles per hour, and the speed of light is measured by the distance it travels in a year. The rate of a chemical reaction is measured as the change in concentration (mol/L) per second.
CO (g) + NO2 (g) -> CO2 (g) + NO (g)
t2 – t1 = ∆[NO]
t2 – t ∆t
[ ] = molar concentration
t = time (s)
∆ = change

9. Reaction Rate Calculation Example
t1 = 0.00 sec
t2 = 2.00 sec
[NOt1] = 0.00 M
[NOt2] = 0.01 M
0.01 M – 0.00 M = M = mol/L · s
2.00 sec – 0.00 sec sec

10. Practice Problems
1. Determine the rate of reaction of a 1.0 M concentration of chlorine when it changes during a reaction to a 0.0 M concentration in 10 seconds.
Determine the rate of reaction of a 2.4 M concentration of hydrogen when it changes during a reaction to a 0.00 M concentration of hydrogen in 6 seconds.
3. Determine the rate of reaction of a 1.6 M concentration of calcium when it changes during a reaction to a 0.2 M concentration of calcium in 40 seconds.

11. Collision Theory
Reaction rates are actually calculated from experimental data. However, looking at chemical reactions on a molecular level provides us with a clear picture of what reaction rate measures.
Have you ever seen a demolition derby in which the competing vehicles are constantly colliding? Each collision results in the demolition of one or more vehicles. In a chemical reaction, reactants must also come together in order to form products.

12. The Collision Theory
The Collision Theory states that atoms, ions, and molecules must collide in order to react. The more collisions that occur between atoms, ions, and molecules; the faster the reaction. However, in reality, detailed calculations of the number of molecular collisions that actually occur in a reaction yield a puzzling result – only a small fraction of collisions produce reactions.
For a collision of atoms, ions, and molecules to produce a reaction a collision must have:
1. Correct Orientation
2. Sufficient Energy

13. Orientation and Activated Complex
Correct orientation requires that molecules, ions, and atoms strike each other with the correct atoms in the molecules coming into contact.
Animation – Collision Theory
If this occurs, an activated complex is formed which is a temporary unstable arrangement of atoms that may break apart to form products. The activated complex is also called the transition state.

14. Activated Complex
Another critical factor that will determine if an activated complex is formed is the presence of enough activation energy (Ea).
Animation
Even though molecules, atoms and ions collide in the correct orientation, if there is not enough activation energy (Ea) the atoms, molecules and ions will rebound and not form an activated complex and new product.

15. 1. 2. What Factors Affect the Rate of a Reaction?
In order for something to be produced, what must the molecules do?
Crash Course
What are the two criteria that must be met when particles collide?
For example, how is water produced? What must collide? 1. 2.

16. Mini Lab Activity – I’m Feeling Dizzy
To see how important energy is to controlling a reaction, you are going to design an experiment using marbles and a petri dish.
1. You must find the relationship between temperature, the frequency of collision, and the energy needed to cause a change from reactants to products.
Results:

17. What you have just modeled from the activity was called the activation energy, Ea, of a reaction.
What is activation energy (Ea)?
What can we compare activation energy to?
What is an activated complex and where does it form?

18. Exothermic Reactions
An exothermic reaction is a chemical reaction accompanied by the release of heat. In other words, the energy needed for the reaction to occur is less than the total energy released. As a result of this, the extra energy is released, usually in the form of heat.

19. Endothermic Reactions
An endothermic reaction is a chemical reaction in which heat is absorbed. The energy needed for the reaction to occur is more than the amount of energy released. Therefore, high energy products are formed.

20. What is the difference between the diagrams
What is the difference between the diagrams? Label them as endothermic and exothermic.
How does Ea affect a reaction?

21. Factors Affecting Reaction Rates
Besides correct orientation and sufficient energy, there are other factors that affect the speed of a chemical reaction. These include:
The nature of reactants
2. Concentration
3. Surface Area
4. Temperature
Catalyst
Inhibitors

22. Factors that Affect Reaction Rate - Concentration
Five main external conditions affect reaction rate. The first is the concentration of reactants. Generally speaking, if we increase the concentration of one or more reactants, the reaction will go more quickly. This is simple because the more molecules, the more collisions between molecules, and the faster the reaction will go.

23. Concentration
Reactions speed up when concentrations of reacting particles are increased because there are more atoms, molecules, and ions present to react. This produces more activated complexes and more product.

24. Factors that Affect Reaction Rate - Temperature
The second factor that influences reaction rate is temperature. The higher the temperature of the reaction, the more quickly it will proceed. At higher temperatures, the molecules are moving around more quickly (they have more kinetic energy); this means they will collide with each other with more energy, and it’s more likely that they will overcome the activation energy needed to start the reaction. It’s a general rule of thumb that a 10˚C increase in temperature will double the reaction rate.

25. Temperature
In most cases, increasing the temperature will increase the rate of reaction because atoms, ions, and molecules move faster and collide more often.
By heating a gas from 20°C to 30°C, the frequency of collisions increases by 10%, but the rate of reaction increases 100%.

26. Factors that affect Reaction Rate - Catalyst
The addition of a catalyst will also speed up a chemical reaction. A catalyst speeds up the rate of reaction by lowering the activation energy. Biological catalysts are known as enzymes. The only other important thing you need to remember about catalysts is that they are not consumed in the course of the reaction.

27. Presence of a Catalyst
Catalysts are substances that change the rate of a chemical reaction without being consumed by the reaction.
A catalytic converter changes harmful CO and NO to safer CO2 and N2 using platinum as the catalyst.
2CO + 2NO -> 2CO2 + N2

28. Inhibitors
Inhibitors are catalysts that slow down a chemical reaction.
To keep apples from rotting before they are sold, growers add inhibitors to slow the effect of acetylene gas which causes apples to ripen.

29. Factors that Affect Reaction Rate – Physical State of Reactants
Another factor that affects certain reactions is the physical state of the reactants. For example, if you mix two gases or two liquids, this represents a homogenous reaction, but if reactants are in different phases, for example, if one is a gas and one is a liquid, then the reaction area is limited to the area where they touch each other, and the larger this area, the faster the reaction will proceed. For example, consider a teaspoon of salt dissolving in water. If you were to dump the salt into the beaker of water and let it float to the bottom without stirring it, it would take much longer for it to dissolve than if you stirred the solution.

30. Nature of Reactants
The nature of reactants strongly affects how quickly a reaction will occur, because some substances react more readily than others. Some substances, depending on their position in the Periodic Table, release electrons easier than others. Elements in families 1A and 2A are much more reactive than elements in families 3A and 4A.
Potassium in water

31. Factors that Affect Reaction Rate – Surface Area
The greater the surface area the more atoms, ions, and molecules available to react which causes a faster reaction.

32. Surface Area
The greater the surface area, the more atoms, ions, and molecules available to react and the faster the reaction.

33. Factors That Affect Reaction Rates
Name the five factors that affect the reaction rate:
1. What happens to group 1A elements when they are placed in water?
2. How does concentration affect the rate of a reaction?   
3. What is surface area and how does it affect reaction rate?
4. Popping the Top activity – how does temperature affect the rate of reaction?
5. Mini Lab Activity – Jeanie in a Bottle – How does a catalyst affect the rate of a reaction?

34. Popping the Top – How Temperature Relates to Rates of Reaction
Purpose: You will investigate how temperature can affect the rate of a reaction.
Materials: film canisters, warm water, ice water, room temperature tap water, Alka Seltzer tablets
Procedure:
1. Break one Alka Seltzer tablet in half.
2. Fill the film canister about ½ full of tap water.
3. Very quickly put the tablet in the canister and put the lid on the canister.
4. Try not to scream!!!!!

35. Mini Lab Activity – Jeanie in a Bottle
Purpose: You will investigate a catalyst and write down your observations of a reaction.
Materials: 3% Hydrogen Peroxide, small beakers, yeast packets, manganese dioxide, glass stirring rod
Procedure:
Pour about 10 mL (the exact amount is not important) into a small beaker.
Add a pinch of yeast to the beaker and observe while stirring with the stirring rod.
Pour out the beaker in the sink.
Repeat steps 1 and 2 with the manganese dioxide.
Pour out the contents of the beaker in to the sink.
Data and Questions
What did you observe with the yeast and manganese dioxide? Did you see the same thing?
Were these homogeneous or heterogeneous catalysts?
Equilibrium
What is equilibrium and how is it measured? 1.

36. This graph represents the energy of particles at two different temperatures. T1 is at a lower temperature than T2.
A. What do you notice about the height of the hills? Which one is higher?
B. Notice that curve T2 is shifted relative to T1. What happened to the number of particles as the temperature increased relative to the activation energy?
C. If you wanted to increase the rate of reaction, how would you do it according to the chart?
D. Based on what you wrote, why would your guess work?

37. Look at the chart below. Can you figure out how a catalyst works?
Answer:
What can we use to slow down the rate of reaction? ________________
Inhibitors:
What is the difference between a homogeneous catalyst and a heterogeneous catalyst?
homogeneous catalyst
Example
heterogeneous catalyst

39. Please answer the following questions on a separate sheet of paper:
What does the reaction rate indicate about a particular chemical reaction?
How is the rate of a chemical reaction usually expressed?
What is chapter 17 about?
What factors affect the reaction rate?
What is the formula for average rate?
How are reaction rates expressed?
Are reaction rates positive or negative?
What is the difference between M and mol/(L· s)
9. What do brackets around a formula represent?