CHEM 101 1nd Edition Lecture 23Outline of Last Lecture I. Measuring Heat of CombustionII. Measuring Heat of ReactionsIII. Using Standard Enthalpy ValuesOutline of Current Lecture I. Radiation II. Electromagnetic SpectrumIII. Electromagnetic RadiationIV. Quantization of EnergyCurrent LectureI. Radiationa. 1864 James Clark Maxwell developed a mathematical formula for radiationb. Wavei. Wavelength (λ): distance between identical loins on successive waves1. Units: Metersa. nm (10-9 m)b. Awith circle on top (10-10 m)c. pm(10-12 m)ii. Frequency: number of wavelengths that pass trough a particular loin in one second.1. Use the Greek letter "nu," ν, for frequency, and units are cycles per second2. Units: Secondsa. Hz(s-1)b. MHz (106 Hz)iii. The speed of visible light and all other forms of electromagnetic radiation in a vacuum is constant1. c = velocity of lighta. = 2.9979 x 108 m/sec (6.7 million mph)iv. For problems1. c = λ x ν2. And put in units of the problemThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.II. Electromagnetic Spectruma. Long Wavelength = Small Frequencyb. Small Wavelength = High FrequencyIII. Electromagnetic Radiationa. If you heat a piece of metal to a high temperature, electromagnetic radiation is emitted with wavelength dependent of the temperaturei. At low temperatures the color is dull redii. As temperature increases the color brightensb. At the end of the 19th century, scientists were not able to explain the relationship between the intensity and the wavelength for radiation given off my heated objectsi. Theories at the time predicted intensity should increase continuously with decreasing wavelengthii. This did not prove true and was called the ultraviolet catastrophe becausepredictions failed in this region. IV. Quantization of Energya. In 1900, Max Planck offered an explanation for the ultraviolet catastrophe.i. Planck assumed that the electromagnetic radiation emitted was caused by vibrating atoms (called oscillators) in the heated objectii. He proposed that each oscillator has a fundamental frequency of oscillation and that the emitted radiation could only have certain energies. b. An object can gain r lose energy by absorbing or emitting radiant energy in QUANTAi. Energy of radiation is proportional to frequency1. E = h x νa. h = Planck's Constanti. 6.6262 x 10^-34 Jxsb. ν = frequencyc. c = speed of lightd. λ = wavelengthe. ν = c/λii. Light with large λ (small ν) has a small Eiii. Light with small λ (large ν) has a large Ec. Examplei. Calculate the energy of 1.00 mol of photons of red light. λ = 700. nm, h = 6.6262 x 10-34 Js, 1 mol = 6.02x10231. E= hν2. ν = c/λ3. E = hc/λa. (6.6262x10-34Js)(2.998x108 ms) / (700 x 10-9) = 171.6
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