Energy Levels And Using Energy To Create Chemical Change

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Chemistry

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Feb 20, 2024

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Click here to erase all data entry on this page E Energy Levels Purpose To understand the origins of Quantum Theory using a spectrometer to observe the emission spectrum of several gases. Connections to What You Already Know About in Life Mercury vapor is used in fluorescent light tubes. The emitted visible light is not very bright for just the mercury vapor, but when scientists examined the full spectrum for mercury they saw that there is an enormous emission in the ultraviolet range (UV). This light is sometimes called black light, and you may have seen it in glow-in-the-dark displays. Fluorescent light tubes are coated with a compound that will absorb UV and emit the energy as visible light with all the colors of the rainbow. All colors together create white light which is why fluorescent light tubes emit very white light. Laundry detergents contain small amounts of a compound that absorb UV light and emit visible light. These compounds allow advertisers to claim whiter and brighter whites and colors . If you attend an event using black lights, you may have seen your white socks or white shirt “glow”. Vocabulary Emission spectrum, spectroscopy, fluorescent Background The classical picture of atoms would allow electrons to be at any energy level. According to this classical model, when electrons are excited and then fall back down to the ground state, they emit light at all wavelengths and the emission spectrum would be continuous. In the 1800s scientists found that when a sample of gas is excited by an alternating electric current, it emits light only at certain discrete wavelengths. This allowed for the development of spectroscopy which is used in the identification and analysis of elements and compounds. Even though scientists found spectroscopy very useful, they could not explain why the spectrum was not continuous. The explanation of this was left to Niels Bohr, a Danish physicist. Bohr proposed that energy levels of electrons are not continuous but quantized. The electrons only exist in specific energy levels. Because of this quantization of energy, excited electrons can only fall to discrete energy levels.

You can separate the lines in the full region of an emission spectrum by using an optical prism or a diffraction grating. A spectrometer is an instrument designed to separate the emitted light into its component wavelengths and plots the intensity of the light as a function of wavelength. This assignment illustrates the measurements that helped Bohr develop his quantum model, now known as Quantum Theory. It also illustrates some practical uses for this science. Mercury vapor is used in fluorescent lights and sodium vapor in street lighting. Procedure Section 1 1. To start this activity, click this link for Energy Levels . The lab will load in a new tab. Click back to this tab to read further instructions and complete the questions below. You can follow along with the instructions below in the Procedures tab in the lab. Questions 1. The lab table will be set up with four items. What is the detector on the right? spectrometer 2. What is the metal sample in the center of the table? tungsten 3. A heat source is used to heat the metal sample to high temperatures. What is the temperature of the heat source? 3000 K Procedure Section 2 1. Click on the Visible/Full button in Live Data to change the view to the visible spectrum. Click the Save Screen button (red dot on the spectrometer window) to record this spectrum in the Lab Book. Open the Lab Book tab in the tray. Type tungsten metal in the Notes box and click enter. Record your observations in the data table below. 2. Click this link to load the next lab setup: Photoemission of H 2 Gas. Save this spectrum in the Lab Book. Add the note to the Lab Book that this is Hydrogen Gas. Record your observations

below. 3. Open the Stockroom tab. Expand the Gases menu. Click on the Ne label to select neon as the gas and it will fill the gas sample tube. If you point to the gas sample tube it will read Gas ( Ne) . 4. Save this spectrum in the Lab Book and add a note with the name of the element typed after the image. 5. Continue with this same process until your completed samples include the following: H 2 , He, Ne, Na, and Hg. You should have five spectra saved in the lab book in addition to tungsten metal. Record your observations for each element. You can return to the Lab Book and to view any of the spectra again. Include in your observations a comparison for each element to the spectrum for heated tungsten metal. Sample Spectrum Observations W We are able to see a wide range of wavelengths which makes the spectrum very visible throughout the whole thing. We are able to clearly see all shade of colors throughout the spectrum which covers the whole screen. H 2 I am only able to view clearly 3 lines in the spectrum which is a red, cyan, and blue lines. The first line is a very very dark blue line that is not very clear to view unless zoomed in. He I am able to see more line in the spectrum. I am able to see 7 lines which are a red, yellow/orange, green, baby blue two times, a blue, and then a dark blue that is hard to see. Ne For Ne, there is multiple different lines I see in the spectrum ranging from a very dark purple to a very dark red. I can roughly say I see like 50 lines as an estimate. Na For Na, I see similar to Ne but there is more lines in the blue side of the spectrum. The one that stands out the most is the gold line in the middle of the spectrum. Hg This spectrum is very similar to Na and a bit like Ne. This one you see more lines in the yellow area. What stood out to me was the blue side where there is a huge one that strikes straight up.

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Questions 4. How do your observations of these gas emission spectra help confirm Quantum Theory? Every moving particle or substance whether it is to be micro or macroscopic it will be associated with a wavelength which is what we noticed in every sample we put in this lab. 5. What differences do you see when changing between the Visible and Full spectrum for mercury? when it comes to visible we are able to see a closer range where we see more lines in this area while when we change it to full spectrum, we see the whole thing which range from 80nm to 990 nm. Visible is 400nm to 700 nm. 6. What distinct feature do you see in the sodium spectrum? Why do you think astronomers are excited about cities changing from normal street lights to sodium vapor street lights? I notice the ranges are much longer and we can tell there is a huge spike of intensity. There is a huge spike on the yellow/orange area on the spectrum. This helps because they are monochromatic which allows to filter the light giving less glowly sky.

Click here to erase all data entry on this page E Purpose To measure temperature changes in a chemical reaction and infer whether the reaction is endothermic or exothermic. Connections to What You Already Know About in Life Every time you use heat to cook food, you are using energy to drive a chemical reaction! Or when you drive somewhere and burn fuel in your car you are using the energy created in a chemical reaction for your benefit. Most chemical reactions involve some change in energy and you just have to know where to look to see that change! Vocabulary Endothermic, exothermic Background Energy changes occur during chemical reactions. Some reactions absorb energy. Energy must be added to these reactions to cause them to occur. Reactions that absorb energy that are known as endothermic reactions. Other reactions release energy. Reactions that release energy are known as exothermic reactions. Procedure 1. To start this activity, click this link for Using Energy to Observe Chemical Changes . The lab will load in a new tab. Click back to this tab to read further instructions and complete the questions below. You can follow along with the instructions below in the Procedures tab in the lab. 2. A bottle of sodium chloride (NaCl) is on the lab bench. A weighing paper is on the balance with approximately 2 g of sodium chloride (NaCl) on the paper. 3. The calorimeter on the lab bench contains 100 cm 3 water. In the Thermometer section of the Live Data tab, click Save Data to begin recording data. Allow 20-30 seconds to obtain a baseline temperature of the water. 4. Drag the weighing paper with the sample to the calorimeter until it snaps over it. Pour the sample in the calorimeter. You can click on the Accelerate button (the red clock) to accelerate the time in the laboratory. Observe the change in temperature until it levels off

and then record data for an additional 20-30 seconds. Click Stop Saving . Open the Lab Book tab in the tray and you will see a data table with all of the data from the experiment. Record the initial and final water temperatures in the data table below. 5. Open the Presets menu in the tray and click on Lab Preset: Heat of Solution – NaNO 3 and repeat the experiment with sodium nitrate (NaNO 3 ). Record the initial and final temperatures in the data table. 6. Open the Presets menu in the tray and click on Lab Preset: Heat of Solution – NaAc and repeat the experiment with NaCH 3 COO (NaAc). Record the initial and final temperatures in the data table. 7. Find the change in temperature for each mixture and record the results in the table. Change in Temperature = Δ T = T 2 – T 1 Mixture Initial Temp T 1 (°C) Final Temp T 2 (°C) Change in Temp T 2 -T 1 (°C) NaCl (s) + H 2 O (l) 24.99 24.78 -0.21 NaNO 3 (s) + H 2 O (l) 25 23.98 -1.02 NaCH 3 COO (s) + H 2 O (l) 25 25.99 0.99 1. An exothermic process gives off heat. The reaction mixture warms up and the sign of the change in temperature is positive. An endothermic process absorbs heat. The reaction mixture cools off and the sign of the change in temperature is negative. Which solutions are endothermic and which are exothermic? The experiments with exothermic process would have to be the heat of solution NaAc. The temperature started at 25 and rose to 25.99 Celsius. The change was almost 1 C. As for the endothermic it would be heat of solution NaNo3 and NaCl. The temperature decrease compared to starting temperature.

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2. Which solutions had little or no change in temperature (less than 0.30 °C)? The one that had little to no change would be the first part of the lab which was the mixture of sodium chlorine NaCl with H2O (water) it I only changed -0.21 C. 3. When sodium chloride dissolves in water, the ions dissociate or break apart in solution. NaCl ( s ) Na + ( aq ) + Cl - ( aq ) Write ionic equations, similar to the one above, that describe how NaNO 3 and NaCH 3 COO dissociate as they dissolve in water. Include heat as a reactant on the left side of the equation or as a product on the right side of the equation. → For NaNO3= (NaNO3)+(heat)—>(Na+)+(NO3-) this is an example of endothermic reaction since we used heat to create a dissociation. For NaCH3COO= (CH3COONa)—>(Na+)+(CH3COO-)+ heat this is an example of exothermic reaction since it causes to release heat during dissociation. Edit Insert Formats                        P 

Energy Levels And Using Energy To Create Chemical Change

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