Calorimetry and Hesss Law Essay Example for Free

Calorimetry and Hesss Law Essay Elemental magnesium is one of the principal components of flares used to illuminate nighttime activities, or to aid in signaling one’s location to aircraft and ships. Your instructor may ignite a strip of magnesium ribbon to demonstrate the combustion of magnesium in air. It will be evident that a great deal of light energy is released from this reaction. A direct method for measuring the heat produced by this reaction would be difficult, so we shall resort to an indirect method in this experiment as discussed below. Some chemical reactions (including the one above) are associated with the evolution of thermal energy and are called exothermic reactions. When there is absorption of energy in a chemical reaction, the process is called endothermic. The magnitude of the energy change is determined by the particular reaction as well as the amount of product(s) formed. The thermal energy transferred in a balanced chemical reaction carried out at constant pressure is called the enthalpy of reaction (or heat of reaction) and is  given the symbol ΔHrxn. ΔHrxn is often expressed in units of kJ/mole where mole refers to the amount of a reactant or a product involved in the reaction. In general, the reactant or product must be specified. In this experiment, you will measure the enthalpy changes of several exothermic reactions utilizing a simple calorimeter. This calorimeter consists of an insulated vessel (a Styrofoam cup), a thermometer, and a lid (which is loose fitting to allow the pressure to remain constant. The energy given off by any reaction carried out in the calorimeter is absorbed by both the calorimeter and the solvent (water). This causes an increase in the temperature of the calorimeter and solvent that can be me asured by a thermometer. The heat that is absorbed by the calorimeter and solvent is calculated from the equation: qcal = C â‹… ΔT (1) where C is the heat capacity of the calorimeter and solvent, and ΔT is the change in temperature of the water (the solvent) in the calorimeter. Heat capacity is defined as the amount of energy required to raise the temperature of an object by 1  °C. In this experiment, the vessel and the amount of solvent remain constant, so C is a constant. Enthalpy is an extensive quantity, so the amount of heat generated by the reaction is given by the expression: qrxn = n â‹… ΔH (2)  where n is the number of moles of a specific reactant or product and ΔH is the enthalpy change of the reaction in kJ/mol. Since the energy of the universe is conserved, the total energy change of the system (the reaction) and surroundings (calorimeter and solvent) is equal to zero. These relationships can be combined as shown in equation (3). qsystem + qsurroundings = qreaction + qcalorimeter = n⋅ΔH + C⋅ΔT = 0 (3) This equation can be rearranged to determine either C or ΔH as shown in equations (4) and (5). C = − n⋅ΔH/ΔT (4) ΔH = − C⋅ΔT/n (5) For exothermic reactions, ΔH 0 and ΔT 0. The main experimental problem in any calorimetric measurement is obtaining an  accurate value of ΔT. The initial temperature, Ti, of the reactants can be determined directly using a thermometer. However, it is difficult to obtain a precise value for the final temperature, Tf (the instantaneous temperature when the reactants are mixed together and react), because (1) reactions do not occur instantaneously, and (2) calorimeters are not perfectly insulating, but actually allow some heat energy to slowly enter or escape from the calorimeter over time. This occurs both during the reaction and after its completion. If an exothermic reaction occurs in a hypothetical calorimeter that is perfectly insulated, all of the heat produced by the reaction will remain in the calorimeter, resulting in a constant final temperature. This would yield the same ΔT whether or not the reaction is instantaneous. Now consider a hypothetical exothermic reaction that occurs instantaneously, but in a realistic calorimeter that is not perfectly insulated. In this case, the temperature of the calorimeter would diminish over time due to the gradual escape of heat energy to the surroundings. ï€  The â€Å"final† temperature to be used in determining ΔT in this case is actually the maximum temperature reached immediately after reaction occurs, since this temperature change is due exclusively to the heat produced in the reaction, and no escaping of heat to the surroundings has occurred yet. For real calorimeter experiments, reactions neither occur instantaneously nor are calorimeters perfectly insulated. Thus, during an exothermic reaction the temperature of the calorimeter increases initially, but never has a chance to reach the correct maximum â€Å"final† temperature since heat is escaping to the surroundings even while the reaction is proceeding toward completion. A correction for this heat exchange is made by an extrapolation process using the temperature vs. time curve (see Figure 1). First, a plot of the temperature readings as a function of time for the reaction is generated. By extrapolating only the linear portion of the curve (e.g., the points including and after the maximum temperature) back to zero time (the time when the reactants were mixed in the calorimeter), Tf is obtained. The Tf value determined in this manner will be the temperature that the calorimeter and the solvent would have reached, had the reaction occurred instantaneously and with no heat exchange to the room. This value should be used for the calculation of change in temperature, ΔT. Consult with your TA for specific instructions for extrapolation using Microsoft Excel. A. Determination of the Enthalpy of Combustion of Mg Using Hess’s Law The calorimeter will be used to determine the enthalpy of combustion of magnesium by application of Hess’s law. Consider the following reactions: (a) H2(g) +  ½ O2 (g) → H2O (l) ΔHa = − 285.84 kJ/mole (b) Mg(s) + 2 H+ (aq) → Mg2+ (aq) + H2 (g) ΔHb (c) Mg2+ (aq) + H2O (l) → MgO (s) + 2 H+ (aq) ΔHc By adding equations (a), (b), and (c) we obtain (d) Mg (s) +  ½ O2 (g) → MgO (s) ΔHrxn = ΔHa + ΔHb + ΔHc which represents the combustion of Mg(s). Reaction (a) represents the formation of liquid water from its constituent elements. The enthalpy change for this reaction, symbolized ΔHa above, is the standard heat of formation of liquid water (or ΔHf (H2O)) and is a known quantity. ΔHb and ΔHc will be determined experimentally by measuring the temperature rise when known masses of magnesium metal and magnesium oxide, respectively, are added to hydrochloric acid. Reaction (c) as written is an endothermic reaction. Since it is easier to perform the reverse (exothermic) reaction, the data you collect will be of opposite sign to that needed for the Hess’s law calculation for reaction (d). When data from your analysis is correctly combined with that for the known reaction (a), the enthalpy of combustion of magnesium metal can be obtained. PROCEDURE: Note: Handle the Styrofoam cups gently. They will be used by other lab sections! A. Determination of the Enthalpy of Combustion of Magnesium Reaction of Magnesium Metal and Hydrochloric Acid 1. Using the graduated cylinder, add 50.0 mL of 1.0 M HCl to the empty calorimeter. Wait for a few minutes to allow the set-up to reach thermal  equilibrium. 2. While waiting, determine the mass of a sample of magnesium ribbon (about 0.15 g) on the analytical balance, and then wrap it with a piece of copper wire. The copper will not react in the solution; its purpose is to prevent the magnesium from floating to the surface during the reaction. Do not wrap the magnesium too tightly or it will not react quickly enough with the HCl solution. Do not wrap the magnesium too loosely since it may escape the copper â€Å"cage† and float. 3. Using LoggerPro, start a run of 500 seconds with the temperature probe in the 1.0 M HCl in the calorimeter (with lid). 4. The magnesium/copper bundle is added to the HCl solution. Replace the lid with the thermometer in place, and begin swirling to mix. Be sure to support the temperature probe. Continue swirling and collecting data and record about 300 seconds or until the temperature starts decreasing. This will provide the linear part of the curve, and are the most important points for the extrapolation procedure. 5. When data collection is completed, rinse the calorimeter and thermometer with distilled water and dry as completely as possible. Place the piece of copper in the container labeled â€Å"copper waste.† B. Reaction of Magnesium Oxide and Hydrochloric Acid 1. Place 50.0 mL of 1.0 M HCl into a clean graduated cylinder. 2. On a top-loading balance, transfer approximately 0.7 to 0.8 g of MgO to a clean weighing boat (no need to record this mass). Next, determine the mass of the MgO and the weighing boat on the analytical balance and record the data. Transfer the MgO to the dry calorimeter. 3. On the analytical balance, record the mass of the â€Å"empty† weighing boat after the transfer and calculate the mass of MgO actually transferred to the calorimeter. 4. Record the initial temperature (Ti) of the 1.0 M HCl solution in the graduated cylinder. 5. Note the time (time = zero) and add the 50.0 mL of 1.0 M HCl to the calorimeter containing the MgO. 7-8 points after the temperature maximum. In this reaction all the MgO should react since HCl is used in excess. However, if the solid MgO is allowed to sit on the bottom or sides of the cup it will not dissolve and hence it will not react. Make sure the solution is mixed constantly but gently. (NOTE: Before discarding this solution, check to see that all of the MgO has reacted. If solid MgO remains, the results from this portion of the experiment are not accurate. If any solid is present, this portion of the experiment must be repeated.)  6. When data collection is completed, rinse the calorimeter and thermometer with distilled water and dry as completely as possible.

Stock Market crash of 1929 (present form) :: essays research papers

  Ã‚  Ã‚  Ã‚  Ã‚   Before World War I only small fractions of Americans invested or had interest in the Stock Market. Many Americans thought of Wall Street with fear and loathing. Populist politicians denounced Wall Street as the center of financial shell games thought up by millionaire operators like Gould, Drew, Morgan and others.   Ã‚  Ã‚  Ã‚  Ã‚  But with the conclusion of the War, many of Americans were getting a different perspective of the Stock Market. Many lost fears of investing due to many were previously buyers of Liberty Bonds. Many Americans assumed they knew the advantages of investing and knowledgeable about stock splits, margin accounts, dividends, etc. New financial methods, the investment trust offered new approaches to investing in the market and many major corporations such as General Motors, General Electric and AT&T offered common stock and bonds were starting to boom and attracted many new money-seeking investors.   Ã‚  Ã‚  Ã‚  Ã‚  And till last month, the market was center of conversation, talked about and financial advice was shared everywhere! The market continued to increase, Major Corporations stocks rose incredibly. But brokers loans reached $137 million, and New York’s banks were in debt to the Federal Reserve by $64million. Warning signs began to appear in the market, and many market analysts began predicting the crash. Throughout the nation, thousands of investors were margin trading, buying stock on credit. The margin trader bought stock by paying less than the full price. This was highly profitable but extremely risky. If the stock value decreased the customer had to invest more money to sustain the account. And if the stock kept falling, the customer would run out of their money, and the broker, who usually borrowed money from their banker, was forced to sell out the account for any amount offered. If the customer could not pay the broker, the broker was unable to pay the banker, which placed of them all in debt.   Ã‚  Ã‚  Ã‚  Ã‚  Many banks wanted their money from brokers, brokers wanted their money from customers, and the only method most customers could get their money was by selling their stock. And so there were massive rapid sales that totaled to nineteen million shares on Friday the 25th of October. The selling of the stocks depressed the market, in other words caused the stock market crash.   Ã‚  Ã‚  Ã‚  Ã‚  Yesterday, on October 29, 1929 also known as â€Å"Black Tuesday,† was the most devastating day in economic history, a total of 16, 410, 030 shares were sold.

Workplace Ethical Dilemma Paper

Workplace Ethical Dilemma Paper BSHS / 322 Marcia Winter Introduction We've all heard the golden rules: In today’s society it is hard to find a good paying job. When one finds a good paying job, that person needs to do whatever he or she can do to keep that job. Ethics can be a problem in a workplace if someone is asked to do something that they do not feel is right. â€Å"Ethics are about making choices that may not always feel good or seem like they benefit you but are the â€Å"right† choices to make† (Curry, 2011; para 2).In the following, I will discuss a workplace ethical dilemma that I have witnessed in my current employment. I will discuss the essential points of the dilemma and how this dilemma intersects with my personal values. Personal Ethics I have very simple personal ethics and values that I live by. â€Å"Don't hurt, don't steal, don't lie, or one of the most famous: â€Å"Do unto others as you would have done to you† (Curry, 2011; para 2) . I have others but these are the main ones I live by.My parents taught me early in life that if I want to do well in this world and have others respect me than I better remember these ethics and values. Workplace Ethical Dilemma I have been employed for the same medical facility for almost 2 years. I started at the hospital and have worked my way into the clinics. This is a major accomplishment because normally my job does not move their employees around. They like to keep everyone in the same place. When I transferred to my current position I was put in the position to â€Å"spy† on the current workers in the office.I kept the same boss and she knew that there were some issues at my new location. She wanted me to get the scoop on everyone and then report back to her. Now, I love my boss and my job, but she was asking me to do something that I was not ok with. I am not the type of person to gossip about people behind their backs. I like to do my job and go home. I do not wan t to talk about others because I have been on the receiving end and have been the person that others have talked about. It does not feel good. Points of Dilemma When I was asked to spy on my coworkers, I did not know what to say.I kept thinking that my boss was joking with me and was waiting for me to respond in the correct way. I felt like she was looking to see what I would do. I did not talk about it for a couple of days after she talked with me about it. I thought long and hard as to what I was going to do. I did not want to lose my job over this but I really did not want to tell on my coworkers. I did not even know them yet. I kept thinking that I could not work with people I did not trust. I knew that if someone was to spy on me, that I would never be able to trust them. Read also â€Å"Glengarry Glen Ross†Ã‚   by David MametI did not want to break that trust. When my boss approached me a second time, I knew what my answer was going to be. I told my boss that I did not feel comfortable spying on my coworkers. I was waiting for her to tell me that I did have a choice†¦. it is either your job or spy on your coworkers. She surprised me when she told me that she understood my position and respected my decision. I stood their flabbergasted because I did not know what to say. Personal Values Personally, this decision to not do what my boss told me tore at me. I have always been taught to listen to authority.My boss would be my authority. However, I was also told to treat others the same way I would like to be treated. I cannot stand it when people talk about me behind my back. I am a person who confronts problems head on. If someone has a problem with the way I do things than I would want that person to confront me and talk with me about it. I would not like them to go running to the boss and â€Å"tell† on me. I did not want my boss to be mad at me but I also do not want me coworkers mad at me. There would only be a couple of reason why I would tell on my coworkers.One would be if I witnessed one of them doing something very wrong to a patient or to another coworker. An example of this would be if one of my coworkers lied to a patient or to another coworker. This would be against my code of ethics. The other reason would be if one of my coworkers would be stealing from the company. Stealing would consist of stealing money, supplies or cheating on one’s paycheck. There are some people who are very dishonest regarding their time card. â€Å"Employee fraud is on the rise, soaring from $400 billion in lost revenue for U. S. usinesses in 1996 to over $600 billion in 2003. And while many organizations have implemented background checking as a requirement for employment, the majority of employees who steal œ68. 6 percent, according to Association of Certified Fraud Examiners –have no prior criminal record (Wolf; Para 4). Conclusion In conclusion, having good work ethics and values are extremely important. People look at those qualities just as much as they would look at qualifications. Employers want employees who are going to not only show up for work but also does quality work as well.The personal workplace dilemma that I shared is not the only personal workplace dilemma I have had. I am sure in my future I will have more. If I continue to live by my personal ethics and values than I should have no problems with my future dilemmas. References Curry, Myron; 2011; Ethics on the Workplace; retrieved October 23, 2011 from http://EzineArticles. com/12475 Wolf, Ira; 2004; Cheating, Lies and Other Workplace Ethics; retrieved October 23 2011 from http://www. super-solutions. com/EmployeeFraudandWorkplaceEthics. asp#ixzz1bqShnBN4

Alzheimer s Disease A Progressive Deterioration Of Neurons

Almost everyone has experienced the situation where he sees someone familiar, but cannot think of that person’s name, or he has shopped in a mall and cannot remember where the car is parked. Anyone over the age of sixty-five would probably panic, fearing that he has Alzheimer’s disease, since age is a huge risk factor related to memory loss. He may ask himself, â€Å"Is something wrong with me, or am I just getting old?† Much of our population is terrified of developing Alzheimer’s disease or of watching a loved one slowly and gradually fade away. Alzheimer’s disease is the most common cause of dementia, which is when the brain loses the ability to function mostly in keeping short-term memories, progressing to lack of cognitive function, and eventually causing death (Atkins, 2008, pp. 3). 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