A gas has a volume of 1140 ml at 37 ºC and 620 mm Hg pressure. Calculate its volume at STP. 1.900
2.800
3.819
4.1000

3. 0.819L (819 mL)

Explanation: Before we go about solving this, we need to do some conversions prior to using the gas law, the gas law is as follows...

P(atm)*V(L)=n(mol)*r(constant)*T(in kelvin)

So here are all the conversions you need.

620 mm Hg -> 0.816 atm

1140 mL -> 1.14 L

37 C -> 310.15 K

After plugging in our new converted values, we will proceed to solve the number of moles of the gas present, our n value, so our equation will look like this...(Note: Constant r in this case is 0.08206 L*atm/K*mol)

(0.816 atm)(1.14 L) = n(0.08206)(310.15)

Solving for n we get 0.03653 moles.

Now our second part is to figure out the volume AT STP (standard temperature/pressure). In the STP conditions, your temperature defaults to 0 C (273.15 K) and 1 atm. Now there is an easier way to do this, but I'll also show the more comprehensive way. Here is the easier method...

Since 1 mole of every gas occupies 22.4 L at STP, we can simply multiply this by our number of moles. So (22.4L)(0.3653 mol) to give us 0.818272.

However, a more accurate answer can be given like this...

Plugging n back into the same equation and this time resetting pressure to 1 atm and temperature to 273.15 K and conserving our number of moles we get...

(1 atm)(v) = (0.03653 mol)(0.08206)(273.15 K)

v = (0.03653)(0.08206)(273.15)

v = 0.8188 L = 0.819 L or 819 mL