So there is this question in my text book that says us to arrange these following items by increasing density:
Air, exhaust from chimneys, honey, water, chalk, cotton and iron.
Everything is straightforward except for air and chimney exhaust.
My answer was that air is denser than chimney exhaust since the exhaust would be hot, so there would be more spacing between the particles, making it less dense. This can also explain why exhaust goes up through the chimney due to the buoyant force of the air.
But every single online source and my teacher says chimney exhaust is denser than air and their reasoning being it contains carbon particles which make it heavier as seen below:
Who is in the correct? And if my teacher and literally every other online source is correct (basically the matrix) is correct, how are they correct and so how does the exhaust exit the chimney?
Best Answer
The question that you are quoting is a very poor question, since the answer depends on what is being burnt to produce the exhaust from the chimney and how far away from the chimney we measure the density.
It is true that smoke from low-quality coal or wood fuel will contain carbon particles. Although it is initially less dense than the surrounding air when hot (otherwise the chimney would not draw), it will cool quickly after it leaves the chimney and may quickly become more dense than the surrounding air.
However, chimney exhaust from smokeless fuel has fewer carbon particles and is hotter, so it will be less dense than the surrounding air for much longer. This is why smokeless fuel was widely adopted to improve air quality in the UK from the mid-1950s onwards. And the chimney exhaust from a properly designed gas fire contains no carbon particles at all.