I have a few questions, I'll list in description. Please help.

Question

What pressure will 23 g of a CO exert in a 3.5 L container at 89°C (answer in atmospheres and find moles of CO, divide the mass by the molar mass of 28.01 g/mo)?

What is the volume, in L, occupied by 1.58 moles of an ideal gas at 0.937 atm pressure and a temperature of 75°C?

How many moles of helium with a 67 L balloon hold at 25°C and 0.5 atm?

What is the temperature (in °C) of 0.52 moles of gas at a pressure of 1.3 atm and a volume of 7 L?

Answer 1

Hello, Savannah,

The first problem can be solved with the ideal gas law, PV=nRT, where P is pressure, V is volume, n is moles, R is the gas constant, and T is the temperature in Kelvin.

Find the number of moles of CO₂ by dividing the mass by the nmolar mass of CO₂. I get 0.821 moles. I'll use the gas constant of 0.08205 L*atm/K*mole. Volume is 3.5 liters. So we have everything but pressure, which is what we can now calculate.

P = nRT/V

P = (0.821moles)*(0.08201 L*atm/K*mole)*(262K)/3.5L

After cancelling units, we are left with only atm. Perfect, I'm encouraged. Note that the temperature was converted to Kelvin.

Now take a guess at what the answer might look like, so that if there is an error in the calculation we might be alerted. 1 mole of any gas at STP occupies 22.4 liters. We have almost a mole, the temperature is higher than 273K, and we're cramming it all into a 3.5 liter container. The pressure should go up quite a bit under these conditions. Let's find out how much by rearranging the equation to isolate P:

P = nRT/V

Now enter the ata from above. I got 6.9 atm (2 sig figs), which seems high, but we did predict it would go up quite a bit just thinking about the conditions, so I'm happy.

The other 3 problems are answered in the same manner. Make a table of values for each, rearrange the equation, make a guess, and then calculate. A spreadsheet such as Excel makes these caculations easier, and you can review them afterwards and make any necessary changes more easily.

I hope this helps,

Bob