CHEM 200/202. Professor Jing Gu Office: GMCS-213F. All s are to be sent to:

Transcription

1 CHEM 200/202 Professor Jing Gu Office: GMCS-213F All s are to be sent to: My office hours will be held in GMCS-212 on Wednesday from 3:00 pm to 5:00 pm or by appointment.

2 LECTURE OBJECTIVES Chapter 5.3 Enthalpy Write and balance thermochemical equations. Calculate enthalpy changes for various reactions. Explain Hess s Law and use to compute reaction enthalpies.

3 HOMEWORK & EXAM 2 (CHAPTERS 5-6) Homework 5 due 2/23 (TODAY) Homework 6 due 3/9 Quiz 2 is 3/8 Exam 2 is 3/10 at 2 PM Note: OWL HW and Quizzes are due by 11:55 PM on due date

4 LECTURE OBJECTIVES Chapter 5.3 Enthalpy Explain Hess s Law and use to compute reaction enthalpies. Chapter 6.1 Electromagnetic Energy Explain the basic behavior of waves. Describe the wave nature of light. Calculate the light wave properties such as Frequency, Wavelength and Energy. Distinguish between line and continuous emission spectra. Describe the particle nature of light (photon).

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7 USING HESS S LAW ClF (g) + F 2(g) ClF 3(g) H rxn =? These reactions can be used to find H rxn above: 2F 2(g) + O 2(g) 2OF 2(g) 2ClF (g) + O 2(g) Cl 2 O (g) + OF 2(g) H 1 = kj H 2 = kj ClF 3(g) + O 2(g) 1/2Cl 2 O (g) + 3/2OF 2(g) H 3 = kj

8 CHAPTER 6 ELECTRONIC STRUCTURE & PERIODIC PROPERTIES OF THE ELEMENTS

9 LIGHT VERSUS MATTER Light Continuum of radiant energies Matter Discrete Massless Fixed Mass No definitive position Fixed Position Behave like waves (and also particles) Behave like particles

10 WAVES Frequency (ν, s -1, Hz) Number of cycles a wave undergoes in one second Wavelength (λ, m) Distance a wave travels in one full cycle Speed of light (c) c = 3.00 x 10 8 m/s λ = c/ν or ν = c/λ

11 AMPLITUDE (INTENSITY) OF A WAVE Top wave is higher in amplitude compared to bottom wave

12 PROBLEM A sodium streetlamp gives off yellow light that has a wavelength of 589 nm. What is the frequency of this light in Hertz? ν = c/λ

13 PROBLEM FM-95, an FM radio station, broadcasts at a frequency of 9.51 x 10 7 s -1 (or 95.1 MHz). What is the wavelength of these radio waves in meters. ν = c/λ

14 THE ELECTROMAGNETIC SPECTRUM

15 ELECTROMAGNETIC RADIATION Frequency (ν, s -1, Hz) Wavelength (λ, m) Speed of light (c) c = 3.00 x 10 8 m/s (in a vacuum) Planck s constant (h) h = x J s ν = c/λ E = hν E = hc/λ

16 PROBLEM A bright violet line occurs at nm in the emission spectrum of mercury vapor. What amount of energy in Joules must be released by an electron in a mercury atom to produce a photon of this light? ν = c/λ E = hν

17 PARTICLE NATURE OF LIGHT Three major aspects of light make it appear to act like a particle, not like waves: Blackbody radiation The photoelectric effect The emission of light from hot elements

18 BLACKBODY RADIATION Heating up an object will cause its atoms to increase in kinetic energy (due to increased vibrations) and emit light (e.g. heating element on an electric stove). Classical physics predicts increasing (infinitely high) amounts of energy being released by objects as hot as the sun. This did not match the observations, where a maximum emission intensity occurs. The birth of quantum mechanics (quantized energy levels).

19 BLACKBODY RADIATION Max Planck proposed that atoms could only vibrate at whole integer values (quantized values with whole integers). New Equation: E = nhν n = 1, 2, 3, 4,. h = x J s (Planck s) Standing waves: a string anchored at each end can be vibrated at certain frequencies result in a certain frequency in a stable wave patter. Each wave has increasing number of nodes (1, 2, 3, 4 )

20 THE PHOTOELECTRIC EFFECT Under certain conditions is was observed that light could knock electrons free from metal plates. Each metal was found to have a discreet threshold frequency for the light, below which electrons would not be ejected The kinetic energy (speed) of the ejected electrons depended on the frequency of the light, not the amplitude (brightness).

21 THE PHOTOELECTRIC EFFECT Einstein proposed that the light hitting the metal should not be viewed as a wave, but as a stream of particles (photons). The energy of the photons depends on their frequency. Ephoton = ɸ + Ekinetic ɸ = work function (metal specific) Ekinetic = max kinetic energy of the electron