# Ch 12.2 Help ## Ch 12.2 Help

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.

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

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.

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.

How to solve:

Daisy
Guest

## Question 1

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

Kathleen
Guest

## Question 4

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

Kathleen
Guest

## Question 2 and 3

Anyone know how to do question 2 and 3?

sedwards
Guest

## Re: Ch 12.2 Help

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

Kathleen
Guest

## Question 2

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!

:-)
Guest

## Q 2&3

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

meg
Guest

## Question 3

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)

Alexa
Guest

## Question 2

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

hwilson
Guest

## Re: Ch 12.2 Help

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!

???
Guest

## Re: Ch 12.2 Help

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

tofu
Guest

## Question 2

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.

Guest24
Guest

## Re: Ch 12.2 Help

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?

boo
Guest

## Re: Ch 12.2 Help

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

boo
Guest

## Question 3

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.

Guest

## Re: Ch 12.2 Help

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

Guest

## Re: Ch 12.2 Help

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.

## most recent question

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

student
Guest

## Re: Ch 12.2 Help

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.

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

jsyz
Guest

## Re: Ch 12.2 Help 