Problems for Exam 2

Question 1

GAS PROBLEMS :
]Given: V1, P1, P2
Solve : V2

Answer 1

V1*P1 = P2 * V2

Thus: (V1*P1)/ V2 = P2

Question 2

GAS PROBLEMS:
Given: “P” “V” “R” “T”
Solve: P2 If decrease V2

Next Solve: If P2 is same but T2 increases by 161.4%

Answer 2

Lets try to ignore R and T because they are constant

(P1 * V1) / V2 = (1*1)/2
P2=1/2

What percentage of 293.15K equals 473.15 K?

#number (473.15K) divided by
#small number  (293.15)
=161.4 % increase in temperature 

thus our pressure too increased from 1.00 ATM to 1.614 ATM

Question 3

GAS PROBLEM: 
Given: P * V = 1
Given: R * T 
Given: Grams/ Mass
Solve: N & Molar mass

OJO! If its Diatomic and you find Grams/Mole to get Molarity. Remember To divide this by 2 again to get N2 H2 O2 etc.

Answer 3

Don’t need to find moles
If PV = 1
Simply : RT*G = Molar mass

Question 4

GAS PROBLEM:
Given: P1 (mmHg) V1 T1, P2 T2
Solve: What is the new Volume?

Answer 4

In this situation a balloon is increasing in altitude =
Decrease in outside pressure (expanding of balloon)
Decrease in temperature
(contracting of balloon)

Convert all mmHg to ATM 
(1 ATM/ 760 mmHg) 
Convert all C to K 
(273.15) 
Find R and N  to get PV=NRT
thus solve for missing V2 since N and R are constant.

Question 5

GAS PROBLEM:
Gives: (Compound + Density=V), T
Solve: Pressure (in mmHg)

Answer 5

With given Compound and Density (g/1L) We know the volume of 1 L.
We can calculate using density and molar mass of compound to find moles N and because it asks of Pressure in mmHg we know to use ATM constant and to finally convert to mmHg in the end.

Question 6

How to Find Density of Air without knowing molar ratio of Air molecules

Given: P V R T
Given :Gas 1 name (mass +container ) Air Gas (mass+container)

*Find Molar Mass

Answer 6

1.) Find molar mass of Gas 1
2. Find possible moles of gas within container
3.) Find grams of Gas1 with found moles and molar mass
4.) Find mass of Just container: Subtract given mass of (gas+container ) from found grams of Gas1 mass
5.) Find Air Mass:
Subtract Air (mass+container) from Just container
6.) Divide found Air Mass by V given

Question 7

How to Find Density of Air
Given percentages of 2 elements composing Air

Given: P V R T

*Find Molar Masses of 2 given elements

Answer 7

Assume Air V is 1 liter. Half of our problem is over, now we have to find how many grams are in Air of 1 liter

Find Air total moles (N) 
Find moles of O2 
Find moles of N2 
(% of O2 X total Air N)
Find mass of O2  
Find mass of N2 
Add together to get Total Air Mass 
D= M / V

Question 8

The following reaction forms 16.5 g of Ag(s):
2Ag2O(s)→4Ag(s)+O2(g)

FIND: Total Volume of gas (O2)

GIVEN:
Balanced Reaction (mole:mol ratio)
16.5 g of one product (Ag)

Temp: 25ºC (298.15)

Total Pressure: 745mmHg

Answer 8

“P” “V”=n,”R”,”T”

Immediate:
Find Moles of Ag with given Mass of Ag= (107.87 g/mol) / (16.5 g of given Ag) = 6.5375 Moles of Ag in problem

Find how many moles within the system (solve for N) :
1.) first find “P” with given pressure: 745mmHg/760mmHg = “.980263 ATM”

2.) Find pressure of system by “V”= NRT/ P

START:
Find moles g of given to find how many moles

Find n of the system