Hydrogen bonds are strong. It takes a lot of energy to break them. Especially when trying to boil 11 L of wort (Wort, BTW, is beer before it gets fermented). Thanks to the high heat capacity of water, getting to the boiling point takes a lot of hydrocarbon fuel.
Tonight I brewed a Brown Ale, and while waiting nearly 30 minutes for the brew kettle to get it's boil on, I had some time to consider the thermochemistry (I linked that page because it has some good math in it and it hasn't been updated in 8 years!!! That is my pet peeve... the lack of updates, not the math.).
When my wife and I bought the stove, we went with for the JGB900SEF GE stove complete with "Power Boil!!!" This baby kicks out 15,800 kJ per hour (15,000 BTU/hr). I was under the impression that this thing should be able to boil 11 L (3 gal) of water in about 3 minutes. Not so (and how silly of me).
Assuming the water starts at 19°C and boils at 104°C (> 100°C due to the boiling point elevation colligative property) the amount of heat needed to raise the temperature by 85° C is: 11,000g x 4.184 J/g °C x 85°C x .001 kJ/J = 3910 kJ.
If the stove kicks out 15,800 kJ/hr, assuming 100% efficiency, it should take about 15 minutes. Obviously, some heat is lost to the surroundings. What I didn't do tonight was measure the amount of time needed to boil the solution. If I do measure that, I will be able to determine how efficient my burner really is.
I don't know how I can survive without knowing this piece of information. Next time I will keep track of the time.
Once the reaction reached a boil. It was kept at a boil for 1 hour. During this one hour 15,800 kJ of heat was produced from the combustion of methane. Methane has a heat of combustion of 900 kJ/mol. During just the boil, I used 15,800 kJ / 900 kJ/mol = 17.5 moles of CH4. That means at 1 atm and 20°C (293 K), I used 420 L of methane gas. That's a lot.
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My supervisor had not heard of the term "colligative" before yesterday afternoon, when I was trying to figure out if the particulate matter hanging in the air over the greater Raleigh-Durham area would cause the rain to not freeze, despite it being 30 degrees F. He was impressed with my ability to spin out an "obscure" chemistry term.
420 L of methane? I crank that out after a bowl of chili. Badda-bing.
I used 420 L of methane gas. That's a lot.
Well sure it seems like a lot when you put it that way.
On the other hand, you could say that it only took 280 g of methane to heat over 11000g of water (and hops and whatever) from 19 to 104 degrees...
Russ.. Good point. It is all relative.
Great article you got here. I'd like to read something more about that topic.
BTW look at the design I've made myself Companionship in London
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