Chemistry
posted by 3.091 .
DECOMPOSITION OF NO2 (10/10 points)
The decomposition of NO2 at room temperature exhibits the following variation in concentration with time:
The concentration of NO2 is expressed in mol/liter, while time is expressed in seconds.
[NO2] ln[NO2] 1/[NO2] Time (s)
0.0831 2.4877 12.03 0
0.0666 2.7091 15.02 4.2
0.0567 2.8700 17.64 7.9
0.0487 3.0221 20.53 11.4
0.0441 3.1213 22.68 15.0
a. Express the rate of decomposition of NO2 as a function of the concentration of NO2 and determine the order of reaction. (numerical response only: 1 = 1st order, 1.5 = three halves order, 2 = 2nd order, etc.)
2  correct
b. Determine the value of the rate constant.
0.71  correct

WOULD YOU WANT TO BE A SILICON RIBBON TWIRLER? (10/10 points)
A silicon ribbon measuring 100 micron thick, 5 mm wide, and 1 m long has 5 volts applied across its long dimension. The resistivity of silicon is 640 ohmm. How much current will flow through the ribbon? Express your answer in Amps.
3.906*10^9  correct

FUN WITH GALLIUM NITRIDE (10/10 points)
Determine if light with wavelength 3.87 x 107 m incident on gallium nitride (GaN) can generate electrons in the conduction band. Gallium nitride has a band gap of is 3.2 eV.
yes  correct
Photons with wavelengths below what value will generate electrons in the conduction band? (Express your answer in meters.)
3.872*10^7  correct

IT'S PLANE SIMPLE! (10/10 points)
Calculate the planar packing density (fractional area occupied by atoms) on the (110) plane of nickel at 300K.
0.5549  correct
Calculate the linear packing density (atoms/cm) for the [100] direction in nickel at 300K.
2.837*10^7  correct

IDENITIFYING ELEMENTS, LIKE A TRANSLATOR (10/10 points)
Determine the chemical element that will generate [mathjaxinline]K_{\alpha} \text{ of 7.725 x $10^8$ $\dfrac{J}{mol photons}$}[/mathjaxinline]. Enter the symbol representing the element below (i.e. enter H for hydrogen, Xe for Xenon, etc.).
Cu  correct

XRAY DIFFRACTION OF AN UNKNOWN METAL, MIGHT BE DANGEROUS (10/10 points)
Last week you and a friend started an experiment to obtain the Xray diffraction peaks of an unknown metal. Through these diffraction peaks you wanted to determine:
(a) whether the cell is SC, BCC, or FCC
(b) the (hkl) value of the peaks
(c) the lattice parameter a of the metal
Unfortunately, however, your friend (since he's not in 3.091) left MIT yesterday, not to return until next semester. All of the data that you could recover from the rubble in his room was the following:
sin^2(\theta) 0.120 0.239 0.480 0.600 0.721 0.841 0.956
You also know that the metal is in the cubic crystal system and the wavelength of the Xrays used is
lambda_CuK_alpha. Using the following information, determine the information you were originally interested in (a, b, and c above).
a. Is the cell SC, BCC, or FCC?
SC correct
b. Enter the hkl value of the peaks as a list separated by commas. Do not put spaces between the values. For instance:
(100),(111),...
(100),(110),(111),(200),(102),(112),(202)  correct
c. Enter the lattice parameter a in Angstroms.
2.24  correct

ELASTICITY, LIKE YOUR SOCKS (10/10 points)
The crystal structure of graphite is shown below. Use the figure to answer the following questions.
Compare the Young's moduli for the directions indicated in the figure. Fill in the blank.
The modulus along a is _________ that along b
equal to  correct
The modulus along a is _________ that along c
greater than  correct
The modulus along b is _________ that along c
greater than  correct
Which of the following reasons best explain your reasoning when comparing the moduli of b and c?
The Poisson ratio is greater than 0.3 in graphite.
The two directions are crystallographically identical
Fundamental bending and stretching of bonds is different in the two directions
Van der Waals bonding has a lower bond strength than colavent bonding  correct
Stretching of covalent bonds requires greater force than bending such bonds
The opportunity to stetch rings in one direction gives one direction a lower modulus
Which of the following reasons best explain your reasoning when comparing the moduli of a and b?
Stretching of covalent bonds requires greater force than bending such bonds
The Poisson ratio is greater than 0.3 in graphite.
The two directions are crystallographically identical  correct
Fundamental bending and stretching of bonds is different in the two directions
The opportunity to stetch rings in one direction gives one direction a lower modulus
Van der Waals bonding has a lower bond strength than colavent bonding

VACANCY IN HOTEL CALIFORNIA (10/10 points)
An activation energy of 5 eV is required to form a vacancy in a metal. At 827oC there is one vacancy for every 104 atoms. At what temperature will there be one vacancy for every 1000 atoms? Express your answer in Kelvin (K).
1150.23  correct

JUST SOME DIFFUSIONAL DATA CRUNCHING (10/10 points)
Consider the data below
Temperature (0C) Diffusivity (m2/s)
736 2 x 1013
782 5 x 1013
835 1.3 x 1012
Given this data, determine the activation energy for the diffusion process (units of Joules per atom or molecule) in this material and the preexponential factor (use units of m2/s).
The activation energy is
2.928*10^19  correct
The preexponential factor is
0.000267191  correct

HYDROGEN STORAGE IN ALLOYS  THE FUTURE? (10/10 points)
Certain alloys such as LaNi5 can store hydrogen at room temperature. A plate of LaNi5 containing no hydrogen is placed in a chamber filled with pure hydrogen and maintained at a constant pressure. At what depth from the surface will the concentration of hydrogen be half the surface concentration after 1 hour? (Express your answer in centimeters). Assume the diffusivity of hydrogen in the alloy is 3.091x106 cm2/sec. Use the approximation erf(x) = x for x with values between 0 and 0.6, if appropriate. Use the Erf Table on the Course Info page for values greater than 0.6.
0.105  correct
The activation energy for H diffusion in LaNi5 is 0.25 eV. How far will the H diffuse (where will it reach half the surface concentration) if the experiment above is repeated at 35°C? (Express your answer in centimeters).
0.124  correct

Chemistry 
DrBob222
Interesting post but I don't see a question.
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