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Assorted General Chemistry Problems

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5.38) Consider the following reaction:
CH3OH (g) ---> CO (g) + 2 H2 (g) deltaH = +90.7 kJ
a. Is heat absorbed or evolved in the course of this reaction? b. Calculate the amount of heat transferred when 45.0 g of CH3OH (g) is decomposed by this reaction at constant pressure. c. For a given sample of CH3OH, the enthalpy change on reaction is 18.5 kJ. How many grams of hydrogen gas are produced? d. What is the value of ΔH for the reverse of the previous reaction? How many kilojoules of heat are released when 27.0 g of CO (g) reacts completely with H2 (g) to form CH3OH (g) at constant pressure?

5.56) A 1.800-g sample of phenol (C6H5OH) was burned in a bomb calorimeter whose total heat capacity is 11.66 kJ/°C. The temperature of the calorimeter plus contents increased from 21.36C to 26.37°C. a. Write a balanced chemical equation for the bomb calorimeter reaction. b. What is the heat of combustion per gram of phenol? Per mole of phenol?

5.64) Given the data
N2 (g) + O2 (g) ---> 2NO (g) deltaH = +180.7 kJ
2 NO (g) + O2 (g) ---> 2 NO2 (g) deltaH = -113.1 kJ
2 N2O (g) ---> 2 N2 (g) + O2 (g) deltaH = -163.2 kJ
Use Hess's law to calculate deltaH for the reaction
N2O (g) + NO2 (g) ---> 3 NO (g)

5.72) Using the values from Thermodynamics Quantities for Selected Substances at 298.15 K (25°C), calculate the value of ΔH° for each of the following reactions:
a. N2O4 (g) + 4 H2 (g) ---> N2 (g) + 4 H2O (g)
b. 2 KOH(s) + CO2 (g) ---> K2CO3(s) + H2O (g)
c. SO2 (g) + 2 H2S (g) ---> 3/8 S8(s) + 2 H2O (g)
d. Fe2O3(s) + 6 HCl (g) ---> 2 FeCl3(s) + 3 H2O (g)

5.114) A sample of a hydrocarbon is combusted completely in O2 (g) to produce 21.38 g CO2 (g), 4.47 g H2O (g), and 311 kJ of heat. a. What is the mass of the hydrocarbon sample that was combusted? b. What is the empirical formula of the hydrocarbon? c. Calculate the value of ΔH°f per empirical-formula unit of the hydrocarbon. d. Do you think the hydrocarbon is one of those listed in Thermodynamics Quantities for Selected Substances at 298.15 K (25°C)? Explain your answer.

6.54) Which of the following are permissible sets of quantum numbers for an electron in a hydrogen atom: a. n=2, l=1, m1=1; b. n=1, l=0, m1=-1; c. n=4, l=2, m1=-2; d. n=3, l=3, m1=0? For those combinations that are permissible, write the appropriate designation for the subshell to which the orbital belongs.

6.60) a. The average distance from the nucleus of a 3s electron in a chlorine atom is smaller than that for a 3p electron. In light of this fact, which orbital is higher in energy? b. Would you expect it to require more or less energy to remove a 3s electron from the chlorine atom, as compared with a 2p electron? Explain.

7.26) Explain the following variations in atomic or ionic radii:
a. I- > I > I+
b. Ca2+ > Mg2+ > Be2+
c. Fe > Fe2+ > Fe3+

7.50) While the electron affinity of bromine is a negative quantity, it is positive for Kr. Use the electron configurations of the two elements to explain the difference.

7.104) Moseley established the concept of atomic number by studying X rays emitted by the elements. The X rays emitted by some of the elements have the following wavelengths.
Element Wavelength (A)
Ne 14.610
Ca 3.358
Zn 1.435
Zr 0.786
Sn 0.491
a. Calculate the frequency, v, of the X rays emitted by each of the elements, in Hz. b. Using graph paper (or suitable computer software), plot the square root of v versus the atomic number of the element. What do you observe about the plot? c. Explain how the plot in part b allowed Moseley to predict the existence of undiscovered elements. d. Use the result from part b to predict the X ray wavelength emitted by iron. e. A particular element emits X rays with a wavelength of 0.980 A. What element do you think it is?

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Solution Summary

Assorted General Chemistry Problems are solved with full working shown.