Question

How do you solve for V2, using Avogadro's Law when moles of a gas are added(n2)? A sample containing 7.20g O2 gas has a volume of 35.0L. Pressure and temperature remain constant. What is the new volume if 0.800mole O2 gas is added?

Answer 1

The new volume is 159 L.

Explanation:

You can read about Avogadro's law at

http://socratic.org/questions/what-is-avogadro-s-law

In your problem,

`n_1 = 7.20 color(red)(cancel(color(black)("g O"_2))) × ("1 mol O"_2)/(32.00 color(red)(cancel(color(black)("g O"_2)))) = "0.225 mol O"_2`

So we have

`V_1 = "35.0 L"`; `n_1 = "0.225 mol"`

If we add `"0.800 mol O"_2`

`V_2 = "?"`; `n_2 = "0.225 mol + 0.800 mol" = "1.025 mol"`

`V_2 = V_1 × n_2/n_1`

`V_2 = "35.0 L" × (1.025 color(red)(cancel(color(black)("mol"))))/(0.225 color(red)(cancel(color(black)("mol")))) = "159 L"`

This makes sense.

The number of moles increased by about fivefold, so the volume should have increased about five-fold (to about 175 L).