Paine College equilibrium point between the reactants (Side A) and products (Side
CHE 105 – Week 5 Formative Assessment. Instructions: • • • • • Each student will work on this assignment alone. Assignments with identical answers will earn grades of zero. If you have questions, you are to ask me, your instructor, not your peers. The assessment will be printed out, completed, scanned, or photographed and uploaded to the upload area. Only assignments uploaded to the class will be graded. You must show ALL work. Submissions with answers only will not be evaluated. Formats: The following formats will be evaluated: • Microsoft Word Note: if you cannot scan your work before submitting, you are welcomed and encouraged to do the following: • • • • Take an image of each page of your work with your phone. Copy/paste those images to a Word document. Make sure the image size is the same as the page. Submit one image per page. Save the file as a Word document. Submitted files in the following formats will NOT be evaluated: • Pages • Lone Jpeg images • Any other file formats *********************************************** Part 1: Reversible reactions. Read Completing this experiment requires that you have already reviewed all of the module material for week 5 and you are comfortable with the definitions of thermodynamics. Please feel free to review if needed. As a brief reminder/introduction, there are two types of reactions in nature: reversible and irreversible. Until only about 200 years ago, it was thought that all reactions were irreversible! The definition of a reaction is when reactants are brought in contact with each other and the result is the breaking or making of bonds to create new materials. If the reaction occurs and the reverse reaction is not possible – if the energy of that process is too great – the reaction is said to be irreversible. A great example of an irreversible reaction is the combustion reaction of Hydrogen and Oxygen to create water. This reaction is required to lift rockets into space – so it’s a good thing that it’s both irreversible and very energetic! Reversible reactions occur when there is at least some ‘back and forth’ between the reactants and the products (as they are shown in a reaction scheme: Reactants ↔ Products In other words, when there are reactants present, products can form, and when there are products, reactants can form. Both processes are the opposites of each other, but both can occur at different frequencies. In this weeks formative assessment, you will be thinking about and demonstrating the conditions around some reversible reactions. Go to the PhET simulation found at :SIMULATIONS > CHEMISTRY > Reversible Reactions. (or – embed here https://phet.colorado.edu/en/simulation/reversible-reactions) Instructions: Open the reversible reactions simulator. Add molecules, and play with the different parameters. Keep in mind that any dots on the left side, are molecules designated A will be reactants and B will be products in a hypothetical reaction. The conversion of A and B is a hypothetical scenario where the population of the dots is what you are considering. In this simulation, you can adjust the following: • • • • height of each side of the reaction height of the ruler number of molecules on each side heat/removal of heat Part 2: Reversible reactions. Doing an experiment. Start the simulaton and add 50 molecules to each side and have the ruler at the top. As they are bouncing around, think about and answer the following questions: 1. Describe what does the ruler in the middle represents? 2. What does the relative levels of sides A and B represent? 3. Heat or cool the reaction – what are we doing to the molecules? What’s happening? 4. If both levels are equal, and the ruler is effectively removed (set to 7) what does this situation represent? 5. Reset the experiment, move both sides to their lowest postions, and move the middle bar to 45. Reset the number of molecules to be the same on both sides. What happens when you increase the heat? 6. What are the conditions under which the numbers of molecules will be different on each side?’ 7. Reset the experiment again. Move the reactant energy platform to some value above the products platform. Record the values and describe where the middle bar is. Does your configuration resemble an endothermic or exothermic reaction? Why do you think so? 8) Move the reactant energy platform to 25. Keep the products on the lowest possible setting. 9) Would you expect this reaction to be endo or exothermic? Why? 10) Which change you made above would best simulate the addition of a catalyst to a chemical reaction. 11) Now move the products to 25 and place the reactants at the lowest possible setting. Start over with some number of new particles, the same number on both sides. What happens? How can we describe this reaction? Part 2: Another experiment. 1) Reset the simulator to have the divider at the maximum level, each platform (reactant/product) at it’s lowest setting, and add 5 particles to one side. 2) Increase the heat to 1000K. What’s happening? If this were a reaction, how would we describe it? What do you think would happen if the divider was removed? 3) Take the divider down slowly. Report what’s happening. Consider this from a chemical perspective. What is being represented here? 4) Plot your experiment. Stop the reaction at 20 second intervals and count the number of molecules on each side over a period of 4 minutes. Time (seconds) 20 sec 40 sec 60 sec 80 sec 100 sec 120 sec 140 sec 160 sec 180 sec 200 sec 220 sec 240 sec Trail 1 A Trial 1 B Trail 2 A 5) Describe what is happening to your data in terms of equilibrium. 6) Will you expect the reaction to ever stop? Why?/Why not? 7) If you let the reaction go on longer, what happens? Trial 2 B
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