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April 27 - May 1, 2016

4/28/2016

Housekeeping: Chapter 6 covers kinetics, which means "movement." In the context of chemistry, it refers to the movement of particles. We have covered the meat of kinetics, but now it is time for you to go back and study the bread. I have given you a set of three tasks that you must complete within the next three class periods. I will provide links and videos to assist you with learning the material.

I am going to combine the Chapter 5 exam with Chapter 6, so you will take just one test. It is easier that way and since your exam is scheduled for May 10, you have plenty of time to master the content in Chapter 6.

Content Review
Textbook: Chapter 6
Mad!Science! Links: Kinetics

Agenda:
Complete the tasks found here and in hard copy.

Lesson Objectives: You should be able to:
1. Explain the factors that affect rates of reaction.
2. Construct a Maxwell-Boltzmann energy distribution curve to account for the probability of successful collisions and factors that affect them, including the effect of a catalyst.
3. Investigate rates of reaction experimentally and evaluate the results.
4. Sketch and explain energy profiles with and without catalysts.

Mission 1: Reaction Mechanisms. The mechanism of a chemical reaction is the series of events that takes place as reactants are converted into products. You can read more about it on ChemWiki. The first video, from Brightstorm, introduces the concept of reaction mechanisms. The second video, which is IB, goes into detail about determining rate laws, which we will deal with soon enough.

Mission 2: Dem Graphs Again!!! Here is a simple graph from the BBC Bitesize website. What do you see?

Here's another. What do you see?

The point of Mission 2 is for you to be able to read and interpret different rate graphs and provide a reasonable explanation as to what is going on, so make sure you pay close attention to the graphs in your text.

Mission 3: Dudes Named Max and Bolt (sort of)...The Maxwell-Boltzmann graph is a distribution curve that shows the distribution of particles in a reaction. Below is a picture from chemguide.edu and a quick YouTube video summary. Study.com has a nice, extensive explanation that will help you answer the questions on the sheet. Copy and paste this link to listen and/or read: http://study.com/academy/lesson/the-boltzmann-distribution-temperature-and-kinetic-energy-of-gases.html

Homework: It is expected for you to complete the tasks in class and for homework. I have given you three periods, so you have the entire weekend plus Sunday to complete the assignment. So by the end of the period on Sunday, both of you should be handing in separate work. If you hand in one complete set of answers, I will split the grade down the middle.

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April 10-28, 2016

4/13/2016

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Housekeeping: You still have not turned in your lab reports. Zeroes will go in the gradebook until they are handed in. If you miss the cutoff date, which is the date of parent-teacher conferences, the zeroes will stay. You have had more than a month to submit your work and it is ridiculous that you cannot keep to a schedule at this point.

We are working in Chapter 5 for the next few weeks. Chapter 5 contains some difficult content and three labs. I am not sure if we will complete all three labs, but we will try. You will have to write up one of those labs, We will go through the schedule for this month and May to figure out when we can get the material covered.

Because this is a lot of material, it is expected that you will work outside of class to keep up with the material. The first part of 5.1 discusses how energy changes are measured and specific heat. The section is 13 pages. We will spend today working on this section. The next day I will see you is Thursday and I plan to cover the second half of 5.1, so it is up to you to make sure you have mastered the content from the first half of 5.1. I will provide practice questions and work packets for you to work on outside of class.

Agenda:
1. 5.1 Discussion and explanation of energy changes.

Lesson Objectives. By the end of this lesson, you should be able to:
1. Explain how heat is a form of energy
2. Describe temperature as a measurement of kinetic energy
3. Explain the conservation of energy in chemical reactions
4. Compare endothermic and exothermic reactions
5. Describe enthalpy changes and how they are expressed under standard conditions.
6. Calculate specific heat problems.

Content Review:
Text: Chapter 5.1 (p. 165-171)
Links: The Physics Classroom The Nature of Energy Measuring Energy Changes

Student Missions:
Mission 1: Energy. Some Days Are Better Than Others.
Some things you should know. Temperature and heat are not the same thing.

Chemical Reactions are accompanied by energy changes. Bonds are broken and formed in reactions which correspond to an increase or decrease in energy, Energy is the ability to do work or move an object against an opposing force. Examples of energy are light, electricity, sound, heat and chemical energy are absorbed or released during chemical reactions.

Heat is energy that results from a temperature change and produces an increase in disorder in how particles behave. Heat increases the average kinetic energy of molecules, which is measured by temperature. The above video discusses the differences between temperature and heat.

The system and surroundings must be defined in any example. The system is the area of interest and the surroundings include everything else. Most systems are open and interface with the surroundings. Some systems are closed and do not interface. The total energy in a system and its surroundings do not change.

Heat contents of a system is called enthalpy A system is a heat reserve. Changes in energy are denoted by "delta H." Delta H is positive when heat is added and negative when heat is released.

Examine the diagram on page 167. It shows the relationship between a system and its surroundings and how they look on an energy curve. Energy curves are endothermic or exothermic.

Enthalpy is stored in chemical bonds and intermolecular forces as potential energy. When substances react, the difference in the enthalpy between reactions and products produces an enthalpy change that can be observed.

Most chemical reactions are exothermic; they g ive off heat and result in a transfer of energy from system to surroundings. Delta H is negative in exothermic reactions. Endothermic reactions absorb heat and result in a transfer of energy from surroundings to system. Delta H is positive in endothermic reactions.

Standard enthalpy changes are a set of conditions (which should be in your data booklet) are the following: 100 kPa, a concentration of 1 mol/dm3 (1M) for all solutions, and all substances in their standard states. Temperature is usually not a part of these conditions, but is normally included as 298K.

Mission 2: Thermochemical Equations. It's better to read this brief section on page 168 and then we will discuss it as a class. These are shorthand ways of conveying information.

Mission 3: Let's Be Specific About This! Specific heat is the property of a substance which gives heat needed to increase the temperature by 1K. It depends on the number of particles present.

The formula for specific heat is

We will complete some practice problems in class today.

Homework: Review the material and finish the specific heat problems. Also complete p. 171 #1-6.

Mission 4: Enthalpy Changes. The direction of change is in the direction of lower stored energy. Chemicals change in a way that reduces their enthalpy. It is expected that a reaction will occur if it leads to a reduction in enthalpy. Products in an exothermic reaction are more stable than the reactants, but stability is a relative term. The sign of delta H is a guide for the likely direction of change, but it is not 100% reliable. Endothermic reactions do occur when there is an increase in the disorder of a system; for example, when gases are produced.

Mission 5: Hess' Law: Addition Gone Wild!! At this point, we are working out of the energetics packet with the practice problems. Energy cycles allow for the calculation of an enthalpy change for a particular reaction calculated from the known enthalpy changes from other reactions. Below are two images: one generic, the other specific.

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April 27 - May 1, 2016

April 10-28, 2016

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