Ch 12.2 Help

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Ch 12.2 Help

Post  Daisy on Thu Nov 13, 2008 3:06 am

Question 1
How many moles are 8.605 x1022 molecules (see sheet 6) ? Indicate with a negative (positive) sign whether the same number of atoms in a metal (do not) make up the same number of moles.

Answer: -0.1429401993355482
How to solve:

Question 2
Hydrogen gas at atmospheric pressure and 13.38 oC occupies a volume of 1.316 cm3. What is the number of hydrogen atoms in multiples of 1020 (divide your result by 1020) (see sheets 6,15). Indicate with a positive (negative) sign whether for helium under the same conditions the number of He atoms would (not) be the same

Answer: -0.6740943669601868
How to solve:

Question 3
An ideal gas in a 9.909 liter container is at a temperature of 23.5 oC and under 0.9156 atm pressure. What is the number of gas molecules in multiples of 1020 (divide your result by 1020)(see sheet 3,14,15). Indicate with a positive (negative) sign whether the number of moles n can (cannot) be calculated from the mass of the gas present and its molar mass.

Answer: 2244.3788764388864
How to solve:

Question 4
The temperature of an ideal gas at 4.984 atm pressure in a closed container is increased from 39.26 oF to 195.4 oF. What is the final pressure in atm (see sheet 3,17 for the "ratio method") ? Indicate with a positive (negative) sign whether one can (cannot) calculate the container volume from the data given.

Answer:-6.543741366524362
How to solve:

Daisy
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Question 1

Post  Kathleen on Thu Nov 13, 2008 2:04 pm

To find the number of moles, do:
Number of molecules/avogadros #
= (8.605e22)/(6.022e23) = .1429

Answer is Negative

Kathleen
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Question 4

Post  Kathleen on Thu Nov 13, 2008 2:12 pm

QUESTION 4
First convert the temperatures to Kelvin, to do this you must first convert the degrees to celsius

C = (Temp in Farenheit - 32) * (5/9)
C+273 = Kelvin temp

So the first temperature is C = (39.26-32) * (5/9) = 4.033 + 273 = 277.033
Second temperature is 195.4 - 32 * 5/9 = 90.777 + 273 = 363.777

Okay, now set up a ratio
P1/T1 = P2/T2
4.984/277.033 = X/363.777
Solve for x
X= (363.777 * 4.984)/277.033
X=6.544

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Question 2 and 3

Post  sedwards on Tue Nov 18, 2008 12:48 am

Anyone know how to do question 2 and 3?

sedwards
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Re: Ch 12.2 Help

Post  Kathleen on Tue Nov 18, 2008 1:33 am

I'll try working on the others once I print the notes

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Question 2

Post  :-) on Tue Nov 18, 2008 4:43 pm

Find n by using the ideal gas law and putting everything into the correct SI units (pressure is in Pascals (101325 Pa = 1atm), volume is in m^3, and temperature is in Kevlin (add 273.15 to the temperature in Celcius)

~ n = [101325 Pa * (Volume in cm^3/100^3)] / [8.31 * Temperature in Kelvin]

Then find the number of MOLECULES in that amount of moles
~ n*Avagadro's number = n * 6.02E23

Then multipy by 2 to get the number of ATOMS (there are 2 hydrogen atoms in a hydrogen moleucle), and lastly, divide by 10^20 to get the answer, which is NEGATIVE

~ [Number of MOLECULES * 2] / 10^20 = - ANSWER!

:-)
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Q 2&3

Post  meg on Tue Nov 18, 2008 5:34 pm

heyy..i still cannot get #2 n 3....can some1 explain it again maybe with numbers??

meg
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Question 3

Post  Alexa on Tue Nov 18, 2008 10:04 pm

main equations: PV=nRT
N=n*Na
Given: P=0.9153atm * 101300Pa/atm = 92719.89 Pa
V=9.909L = 9.909e-3 m^3
T=23.5 C + 273.15 = 296.65 K
R=8.31 J/molK
Solution: PV=nRT
n=92719.89*9.909e-3/(8.31*296.65)=0.3726982553
N=n*Na=0.3726982553*6.02e23=2.2436e23 = 2244 (e20)
Answer is negative

Alexa
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Question 2

Post  hwilson on Wed Nov 19, 2008 11:12 am

I still don't understand question 2 can someone give a more detailed description on this question?

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Re: Ch 12.2 Help

Post  ??? on Wed Nov 19, 2008 1:25 pm

Ikeep getting questions 2 and 3 wrong. for number 3 when your answer is e23 and you divide by 10^20 your answer is going to be in the thousands i dont get an answer with #e20 so i'm not sure how you guys are getting that. Also number 2 i get a big number not in decimal, can anyone help to tell me what i'm doing wrong? thanks!

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Re: Ch 12.2 Help

Post  tofu on Fri Nov 21, 2008 12:52 am

For question 3, the answer came out to be negative for me.

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Question 2

Post  Guest24 on Fri Nov 21, 2008 1:38 am

The solution for question 2 above is right except for the fact that to get to cubic meters you must divide cubic centimeters by 10^6 not 10^3 as noted above.

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Re: Ch 12.2 Help

Post  boo on Fri Nov 21, 2008 2:11 am

for #3 the atm is posted wrong they put101300pa, it is 101325 pa. Ans when putting in the answer do you alsowrite the E20 at the end of the answer? or just the 4 digit answer?

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Re: Ch 12.2 Help

Post  boo on Fri Nov 21, 2008 2:23 am

ok so i figured out for #3 at the end u have to divide by (10^20) and the answer is POSITIVE!!!!!!!!!

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Question 3

Post  Avagadro on Fri Nov 21, 2008 2:30 am

Nice dude I just figured it out too.. you can also try

PV = nRT and leave all the given units except add 273 to the T

Then mult by Avogadro's number and divide by 10^20.

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Re: Ch 12.2 Help

Post  Avagadro on Fri Nov 21, 2008 2:35 am

no typo.. I'm a distant relative of Avogadro

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Re: Ch 12.2 Help

Post  Guest01 on Fri Nov 21, 2008 3:47 am

I am still having trouble with Question 3. My work:
1.1087 atm
2.595 L
24.59 C

(((1.1087*101305)*(2.595/1000))/(8.31*(273.15+24.59))*6.022e23)/1020

The answer I put: 70.9390

Does 101325 really make the difference in the number?

EDIT: Found out it really doesn't.

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most recent question

Post  student on Fri Nov 21, 2008 4:28 am

It's supposed to be
((Patm*101305)*(L/1000)*6.02*10^23) then divide all of this by (celsius temp+273.15)*(8.13) to get something around 10^23 or 10^22 then divide by 10^20

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Re: Ch 12.2 Help

Post  Guest01 on Fri Nov 21, 2008 5:34 am

Doing that I get a value of 112.xxxx

I don't know if one of the constants I'm using is wrong or what.

I guess I can sacrifice 1 point.

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signs

Post  jsyz on Fri Nov 21, 2008 12:47 pm

1.)-
2.)-
3.)+
4.)-

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