## Chapter 8

## Q. 8.8

Using Avogadro’s Law: Finding moles in a Given Volume at STP

Use the standard molar volume of a gas at STP (22.4 L) to find how many moles of air at STP are in a room measuring 4.11 m wide by 5.36 m long by 2.58 m high.

ANALYSIS We first find the volume of the room and then use standard molar volume as a conversion factor to find the number of moles.

## Step-by-Step

## Verified Solution

STEP 1: Identify known information. Length = 5.36 m

We are given the room dimensions. Width = 4.11 m Height = 2.58 m

STEP 2: Identify answer and units. Moles of air = ?? mol

STEP 3: Identify the equation. The

volume of the room is the product of

its three dimensions. Once we have the

volume (in m³), we can convert to liters

and use the molar volume at STP as a

conversion factor to obtain moles of air.

Volume = (4.11 m)(5.36m)(2.58 m) = 56.8 m³

= 56.8 m³× \frac {1000L}{1m³} = 5.68 ×10^{4} L

1mol= 22.4 L→ \frac {1 mol}{22.4L}

STEP 4: Solve. Use the room volume and

the molar volume at STP to set up an equation, making sure unwanted units cancel.