Physics question

[Anonymous No.2429326]

20 g of dry ice (solid CO2) is placed in a 2.0*10^4 cm^3 container, then all the air is quickly pumped out and the container sealed. The container is warmed to 0 deg C, a temperature at which CO2 is a gas.

a) What is the gas pressure? Give your answer in atm. The gas then undergoes an isothermal compression until the pressure is 3.4 atm, immediately followed by an isobaric compression until the volume is 2000 cm^3.

b) What is the final temperature of the gas?
I have no fucking clue where to begin. Physics is not my subject...

[Anonymous No.2429377]

Bump for help!

[Anonymous No.2429395]

PV=nRT, n=mass/Molar mass. find the # of moles of CO2, substitute for n, then solve for P, to start...

[Anonymous No.2429398]

Answer: Read the fucking textbook dumbfuck OR Pay attention in class dumbfuck

[Anonymous No.2429482]

>>2429398
Missed the last two weeks of class with chickenpox. Textbook doesn't make sense, I'm gonna get a tutor next week...

>>2429395
P = nRT / V
Molar mass of CO is 28.010 g mol^-1.
Therefore number of moles in 20 g is 20 g/28.010 g mol^-1 = 0.71 mol.

P = ((.71)(8.314472e15)(-273.15)) / (2.0*10^4 cm^3)

P = -8.062398*10^19 m^3

Is that right ???

[Anonymous No.2429509]

Err, I put the wrong units and gas constant. Here:

((.71 mol)(8.3145 J/mol K)(-273.15 degrees K)) / (2.0*10^4 cm^3) = P = -80624251.5 kg K / s2

That's not right either. Sigh

[Anonymous No.2429530]

>>2429482

going to trust you did the calculations right. doble check your units.

then, isothermal compression = keep temperature constant. if T is constant, and n is constant, then
P1V1 = P2V2
solve for V2, then get ready for part 3 where you keep pressure constant (isobaric) and play around with volume and temperature. You should be able to figure it out from here.

[Anonymous No.2429570]

>>2429530
Did the calculation wrong. Now i've got

((.71 mol)(8.3145 J/(mol*kelvin))(-273.15 degrees kelvin)) / (2.0*10^4 cm^3) = -0.795699496 atm

Not the right answer for pressure. But at least the proper units.

[Anonymous No.2429581]

>>2429570

units Kelvin should be positive, by definition. recalculate.

[Anonymous No.2429592]

>>2429581
80624.2515 pascals or 0.7957 atm

Still not right :<

[Anonymous No.2429602]

>>2429592

are you expressing volume in Litres? (=1000cm^3)

[Anonymous No.2429613]

>>2429602
20L or 20,000cm^3 makes no difference in the result.

[Anonymous No.2429623]

>>2429602
Should I be using 20,000 or 2,000 for the volume?

[Anonymous No.2429726]

Halp!