How much does the air in a room weigh?

Question

Estimate the mass of the air in an ordinary living room, say 4 metres by 5 metres with a 3 metre ceiling. You will need the density of air; if you do not remember it, derive a rough value from the fact that a mole of gas occupies about 22 litres at room conditions and air is mostly nitrogen (molecular mass 28).

Accepted Answer

About 70 kilograms, roughly the weight of an adult. Density of air. One mole of any gas fills about 24 litres at room temperature (22.4 litres at 0 degrees). Air is about 78 per cent nitrogen (28 grams per mole) and 21 per cent oxygen (32 grams per mole), so a mole of air weighs about 29 grams. Density: 29 g / 24 L, about 1.2 g per litre, which is 1.2 kg per cubic metre. The room. 4 × 5 × 3 = 60 cubic metres. Times 1.2 kg per cubic metre: 72 kg. Furniture and people displace a little, so "about 60 to 70 kg" is the answer. Why it surprises. Air feels weightless because we are immersed in it an…

How much does the air in a room weigh?

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