Recitation 2
Name____________________________________
1.) The Watt is the derived SI unit of Power, the measure of energy per unit time: 1W = 1 joule/second.
A semiconductor laser in a CD player has an output wavelength of 780 nm and a power level of 0.10
mW. How many photons strike the CD surface during the playing of a CD 69 minutes in length?
2.) The series of emission lines of the hydrogen atom for which nf = 3 is called the Paschen series.
(a) Determine the region of the electromagnetic spectrum in which the lines of the Paschen series are
observed.
(b) Calculate the wavelengths of the first three lines of the Paschen series—those for which ni = 4, 5, and
6
3.) Write the formulas of each of the following compounds:
a) Mercury (I) chloride
b) Ammonium sulfate
c) Sulfurous acid
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4.) Two elements, R and Q combine to form two binary compounds. In the first compound, 14.0 g of R
combines with 3.00 g of Q. In the second compound, 7.00 g of R combines with 4.50 g of Q. Show that
these data are in accord with the law of multiple proportions. If the formula of the second compound is
RQ, what is the formula of the first compound?
5.) Microwave ovens use microwave radiation to heat food. The energy of the microwaves is absorbed
by water molecules in food, then transferred to other components of the food. Suppose that the
microwave radiation has a wavelength of 11.2 cm.
(a) How many photons are required to heat 200. mL of coffee from 23 °C to 60°C?
(b) Suppose the microwaves power is 900W, how long would you have to heat the coffee in part A?
6.) In the United States, water use for irrigation is measured in acre-feet. An acre-foot of water covers
an acre to a depth of exactly one foot. An acre is 4840 yd2. An acre-foot is enough water to supply 2
typical households for 1.00 years.
a) If desalinated water costs $1950 per acre-foot, how much does desalinated water cost per liter?
b) How much would it cost 1 household per day if it were the only source of water?