# Question #29d0f

##### 1 Answer

No; as a general, rule, don't just take two numbers you see in a question and multiply them together. Look at their units, and see if that makes sense.

In this case,

What you should do instead is recognize that **many gases expand to fill their container**.

So, no matter what pressure the container is held at, in a **there are (likely)** **of air in there**. Only the packing tightness (the density) of the air particles will change, once the particles have distributed themselves evenly.

As for pressure changing over the course of 30 seconds, that's *too long* to assume that it is linear.

In general we can expect that it is too complicated to fit to a linear equation, but we can assume that it does if we remember that it's ** only an assumption**.

When we ** assume** that, if the pressure drops from

#P_1V_1 = P_2V_2#

#=> V_2 = P_1/P_2V_1#

#= 5/4("100 L")#

#=# #"125 L"#

So, the approximate change in volume over time might be:

#color(blue)((DeltaV)/(Deltat)) ~~ "125 - 100 L"/"30 s" xx "60 s"/"1 min"#

#= color(blue)("50 L"/"min")#

but it could be *quite off* depending on what was happening in that timeframe. What if you turned off the valve for 5 seconds and then turned it back on? That's not continuous air flow; that's not