Problem Set 1 (Due at beginning of class on assigned date):

1. Tungsten has been used as a lamp filament since the early 1900s. Incandescent lights operate by passing an electric current through a tungsten filament; electrical resistance results in heating of the tungsten filament to a temperature of approximately 2900ºC. Approximately 90% of the energy expended in incandescent light bulbs is used to generate heat; the rest produces light.

a. Calculate the wavelength at which the intensity of light emitted from this light bulb is at a maximum.

b. Sketch a diagram of wavelength vs intensity illustrating the types and relative amounts of light emitted.

c. The thermodynamic efficiency of coal-fired power plants in the Charlotte region ranges from 25% to 42%. This efficiency is primarily a limitation of the second law of thermodynamics and represents the percentage of heat generated by the coal combustion chemical reaction that is actually converted into electricity. Transmission of electricity across the grid also results in energy losses of 5-10% of the generated electricity. Calculate the overall percentage of heat energy produced from burning coal that is actually converted to light generated by incandescent lights plugged into the grid. Clearly show your rationale, all calculations, and all assumptions.

2. Later in the course, we will examine the generation of tropospheric ozone on hot summer days. One of the steps in this process involves the photodecomposition of nitrogen dioxide (NO₂) to produce nitrogen monoxide (NO) and an oxygen atom. The brown tint of air in polluted cities is primarily due to NO₂ absorption of visible light.

a. Calculate the change in enthalpy for this reaction using the enthalpies of formation table (for NO and NO₂) from your Atkins text. The enthalpy of formation for atomic oxygen is 248 kJ/mole (half the bond enthalpy for O₂).

b. Determine the range of wavelengths (in nm) of light with sufficient energy to photodecompose nitrogen dioxide.

c. Comment on your answer to b in terms of light present at ground level.

3. Baird 1.7

4. Baird 1.9, also draw clearly labeled enthalpy-reaction coordinate diagrams for each of the two reactions.