what is the volume occupied by 16.0g ethane gas (C2H6) at 720 Torr and 18C?

V=nRT/P

conversion of mol:
16.0g C2H6 X 1mol C2H6/30.07g C2H6= .53mol C2H6

V= .53 mol(0.0821 L*atm/mol*K)(291)K /
720 Torr (1 atm/760Torr)

V= 13.5 L

I ALWAYS carry at least one more place than I know I'm allowed and sometimes even two more. You can ALWAYS throw those unwanted numbers away at the end when you round with s.f. in mind; you can't always ADD numbers at the end if you've thrown them away earlier.

I don't get that number exactly. First, I don't think you should have rounded when you did. You are allowed at least 3 s.f. but you rounded to 0.53, throwing away at least 1 s.f. I obtained, using your numbers, 13.37 L, which would be rounded to 13.4 to three s.f. However, using the number in the calculator that comes from 16/30.07 (0.53209), and using the remainder of the figures you have, returns 13.418 which rounds to 13.4L.

I guess I need to figure out the s.f. or stop rounding numbers.... :( thank you...

To find the volume occupied by 16.0g of ethane gas (C2H6) at 720 Torr and 18°C, you can use the ideal gas law equation.

First, let's convert the given mass of ethane (C2H6) to moles using its molar mass. The molar mass of C2H6 is 30.07 g/mol.

16.0g C2H6 x (1 mol C2H6 / 30.07g C2H6) = 0.53 mol C2H6

Now we have the number of moles of ethane.

Next, we can use the ideal gas law equation:
V = nRT / P

where V is the volume, n is the number of moles, R is the ideal gas constant, T is the temperature in Kelvin, and P is the pressure.

R = 0.0821 L*atm/mol*K (This is the ideal gas constant in the correct units for this calculation.)

The given temperature is 18°C. To convert it to Kelvin, we add 273.15.
T = 18°C + 273.15 = 291.15 K

The given pressure is 720 Torr. To convert it to atmospheres (atm), we divide by 760.
P = 720 Torr x (1 atm / 760 Torr) = 0.95 atm

Now we have all the values, and we can plug them into the ideal gas law equation.
V = (0.53 mol)(0.0821 L*atm/mol*K)(291.15 K) / (0.95 atm)

Calculating this expression gives us V = 13.5 L.

Therefore, the volume occupied by 16.0g of ethane gas (C2H6) at 720 Torr and 18°C is 13.5 L.