Question

A balloon filled with 0.01 mol of hydrogen gas is kept constant at 25 degrees Celsius. If the pressure is increased from 1atm to 1.5atm, what is the resulting volume?

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C3H8(g) + 5 O2(g)-->3 CO2(g) + 4 H2O(g)

A 0.03 mol sample of C3H8 is reacted with just enough O2 to use up both reactants in a 1L flask at 300 K. The total pressure in the flask after the reaction is complete is closest to whih of the folowing... (Use R = 0.082)

A) 5.0
B) 0.5
C) 0.1
D) 0.25
E) 0.05

a)
Use PV = nRT
P = 1.5 atm
solve for V
n = 0.01 mols
R = 0.08205 or whatever your teacher has said to use for this number but the units must be in L*atm/mol*K if you use atm for pressure.
T = 298.
I found V about 0.16

b)
Use PV = nRT
Solve for P.
V = 1L
R = 0.082 from the problem.
T = 300 K
n = 0.21
(For every 1 mol C3H8 we get 7 mols, combined, of H2O (as a gas) and CO2 (as a gas). We started with 0.03 mols C3H8; therefore, 7 x -./03 = 0.21

A couple of additions to my post.
The 0.16 for (a) is approximate and the unit is liters.

For (b), I made two typos in the last line. It should read "We started with 0.03 mols C3H8; therefore, 7 x 0.03 = 0.21 mols of gas.

So basically they said "pressure is changed from 1atm to 1.5atm" to confuse you?

and thank you so much for the response. It helped me understand it A LOT more. =]

I suppose that is right, more or less. It really doesn't matter WHAT the pressure was at the start although we could have calculated it if necessary.

Answer 1

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