Chemical Engineering in Life - Question 7 - Standard answers available
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This post was last edited by yjqin1 on 2015-8-20 at 18:54. When I was a child, I tried to make firecrackers on my own; the ratio used was one part nitrate, two parts sulfur, and three parts charcoal. So when I was a child in winter, I had nitrates, sulfur, and charcoal at hand. Nitrate and charcoal were made by myself, while sulfur was stolen from the adults. Looking back now, I loved playing with fire since I was young, but I’ve never caused a fire in my entire life. When charcoal burns, it has almost no smell and no smoke ； When sulfur burns, it has a pungent smell and produces white mist, especially in a warm basement with a fire going, where this mist is quite visible. What’s causing this white mist?
When sulfur burns in air, it produces only sulfur dioxide. Sulfur dioxide absorbs the moisture in the air and condenses into small water droplets, resulting in a foggy white smoke.
When sulfur burns, it produces sulfur dioxide; due to the high relative humidity in the basement, sulfur dioxide gas combines with the water vapor in the air to form water droplets
This is a process in which sulfur reacts with oxygen to produce sulfur dioxide; sulfur dioxide then combines with water vapor to form sulfurous acid mist. This sulfurous acid mist is oxidized to produce sulfuric acid mist, which in turn decomposes into sulfur trioxide and water vapor. Through this repeated cycle, white mist is formed.
Sulfur dioxide is produced as a reaction product; it absorbs the moisture in the air, which then condenses into small water droplets, and that’s when this phenomenon occurs
Charcoal contains sulfur, which produces sulfur dioxide; this can easily turn into sulfurous acid when in contact with water, resulting in white mist
Standard answer: Everyone’s answers are close to the standard answer. Sulfur burns to produce sulfur dioxide, which forms white mist when it comes into contact with moisture in the air. From the perspective of chemical thermodynamics, at this temperature, with the given partial pressures of sulfur dioxide and water vapor, both a gas phase and a liquid phase exist; therefore, a liquid phase is formed from the pure gas phase. A tiny liquid phase is nothing but a droplet; to the naked eye, it appears as white mist. Of course, if the temperature is set to a certain value, according to the phase diagram, the liquid phase disappears, and thus no white mist remains. This question is not difficult to answer. Actually, I used to think that white fog appeared because sulfur dioxide was further (slowly) oxidized to sulfur trioxide, and sulfur trioxide could absorb moisture from the very dry winter air to form white fog. It was not until I started my doctoral studies that I learned this process requires a catalyst; otherwise, the reaction proceeds extremely slowly, even at high temperatures. However, at room temperature, activated carbon can catalyze the oxidation of sulfur dioxide.