Wikipedia:Reference desk/Archives/Science/2021 March 30

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March 30

wolf diet

[1] says a wolf sustains itself (does that mean "eats"?) on 40 pounds of meat per day. That's close to half of a typical wolf's body mass. Can that possibly be right? Even if it only means the wolf kills 40 lb of prey animals, maybe 1/3 of that ends of being edible, so it still seems like a lot. Wolf says some things about diet but not the amount. It seems like a huge caloric intake even for something running around in the snow all day. Is it plausible? Thanks. 2602:24A:DE47:BB20:50DE:F402:42A6:A17D (talk) 15:45, 30 March 2021 (UTC)

That can't be right; maybe 4 pounds would be closer? But 40 pounds of meat would mean consuming an additional 50 percent of its own body mass every day. That seems, um, wrong. Domestic dogs are basically just tame wolves, and a similarly sized domestic dog (which probably has less caloric requirements than a wild wolf) in no way consumes anything near 40 pounds of food. this recommends 4 cups of kibble, which should be roughly 2 pounds. 40 seems WAY off. --Jayron32 16:24, 30 March 2021 (UTC)

"This source". seems more authoritative and points out that they are gorge feeders, so don't necessarily eat every day. That citation says 10 lb a day on average. Incidentally, the source quoted by the OP has a comments section, and someone has pointed out there the figure is too high and suggests 7 lb/day. Depends on your wolf, I suppose.... Mike Turnbull (talk) 16:37, 30 March 2021 (UTC)

Yes, I think "sustains itself" does mean "eats". I know they're not canidae, but I saw this at Tasmanian devil: "On average, devils eat about 15% of their body weight each day, although they can eat up to 40% of their body weight in 30 minutes if the opportunity arises. ​So maybe something like that was what Judith Lavoie intended? Or maybe Victorian wolves are just very gutsy. Martinevans123 (talk) 16:43, 30 March 2021 (UTC)

Wolf#Feeding does say they eat 15-19% of their body weight in a single feeding, which could be close to 15 pounds of meat, but that doesn't say they do that every day (and may not, many wild animals go days between feedings). But that's still not 40 pounds. --Jayron32 16:58, 30 March 2021 (UTC)

References

Thanks everyone. 40 lb/day sounded like it couldn't possibly be right, and that seems confirmed now. 2602:24A:DE47:BB20:50DE:F402:42A6:A17D (talk) 05:43, 31 March 2021 (UTC)

Vehicle Emissions

How can carbon dioxide emissions be reduced/eliminated from internal combustion engines, when the very chemical definition of combustion is: hydrocarbon + oxygen yields Carbon Dioxide + Water? Furthermore, carbon dioxide + water reversibly converts to carbonic acid.68.188.106.194 (talk) 17:42, 30 March 2021 (UTC)

So, there are a couple of things you are confusing here: first of all, emissions from internal combustion engines includes a lot MORE than merely carbon dioxide and water vapor. Incomplete combustion leads to both carbon monoxide and unburnt fuel in the emissions; the catalytic converter in a car is used to reduce these emissions. Secondly, common impurities in fuel lead to production of both sulfur oxides and nitrogen oxides; each of these emissions is more harmful than the CO₂ is. Thirdly, carbonic acid is highly unstable; it only forms under high pressure and low temperatures; at atmospheric pressures and at high temperatures it will not form. The carbon dioxide and water vapor produced by combustion of hydrocarbons does not form any carbonic acid in any appreciable amounts. Those products simple get added to the atmosphere as is, without any further reactions. Now, to answer your question more directly, the way to get internal combustion engines to produce less carbon dioxide is to have them burn less fuel. The amount of CO₂ produced from a given amount of gasoline or diesel fuel is a fixed quantity, so the only way to reduce emissions of CO₂ is to improve fuel efficiency. --Jayron32 18:29, 30 March 2021 (UTC)

Need to disagree with you somewhat regarding carbonic acid. The reason carbonic acid isn't directly produced by the carbon dioxide and water vapor of internal combustion engine burning of gasoline has nothing to do with pressures or temperatures involved, but because of physical states. The formation of carbonic acid in water is an equilibrium process following Henry's Law (I'm oversimplifying and there are a few other important equilibria to consider, but none happen if the Henry's Law equilibrium hasn't happend), which requires the presence of liquid water. The water product of gasoline combustion is gas phase, and so no equilibrium reaction to form carbonic acid will take place directly from the tailpipe. It will still happen elsewhere, though, such as in the ocean. The pH of natural rainwater is about 5.65, for example, largely because of the equilibrium reaction between the liquid water and carbon dioxide in the atmosphere to form carbonic acid. It isn't a lot of carbonic acid, but it is present, and that is at ambient atmospheric conditions. Our increase of carbon dioxide in the atmosphere has had a measurable change on this, both in rainwater (a fairly simple system) and seawater (a much more complicated system that is somewhat more resistant to pH change). See ocean acidification. --OuroborosCobra (talk) 18:42, 30 March 2021 (UTC)

Well, I didn't go into that level of detail because the OP didn't need it. I don't disagree with anything you say there. It is correct, but it is entirely irrelevant to the situation in internal combustion engines. --Jayron32 18:52, 30 March 2021 (UTC)

(ec) Firstly, that's not the chemical definition of combustion. That's the chemical definition of hydrocarbon combustion with molecular oxygen as the oxidant. Combustion itself is just a high temperature exothermic redox reaction involving fuel and an oxidizer. Indeed, our own article on combustion starts with an example that does not have CO2 as a product, that being the combustion of molecular hydrogen with molecular oxygen, yielding just water as a chemical product and no carbon dioxide. Ethanol is another common fuel that isn't a hydrocarbon, though its combustion products (when burned with oxygen) are still fairly similar. Second, physical states are important to include when describing chemical reactions. For example, your second reaction, that being the equilibrium between carbon dioxide gas and dissolved carbonic acid in liquid water, without physical states you might think you would get carbonic acid out of your first reaction (combustion) because both carbon dioxide and "water" are products. You don't, however, as (generally speaking) the products of the combustion of hydrocarbons with molecular oxygen are all gas phase. You won't get an equilibrium of carbon dioxide gas to dissolved carbonic acid in a system where all of the water is itself gas phase, and not condensed. In answer to your overall question, there are two main ways to reduce or eliminate carbon dioxide emissions from internal combustion engines. The first, and most obvious one, is to stop using internal combustion engines. If your car is powered by battery driven electric motors rather than internal combustion engines, you won't have any combustion reaction taking place, and you won't have any carbon dioxide product (at least at the end of the car). The second is to change the fuel or change the oxidizer. We will ignore changing the oxidizer, since ambient air is generally the oxidizer source, rather than any oxidizer carried with the vehicle, so we can assume that we are just going to use molecular oxygen as the oxidizer if we are doing combustion. Changing the fuel very much remains an option. If you use a non-carbon containing fuel, you cannot have any carbon dioxide product, so if you can burn molecular hydrogen in your internal combustion engine, you will have zero carbon dioxide emissions. There may be engineering challenges to putting that into practice. An easier option, from an engineering perspective, is to have a fuel that gives you more extractible work per carbon dioxide emission. Doing so would not eliminate carbon dioxide emissions, but it would reduce them. Ethanol, for example, is looked as an alternative combustion fuel as, even if not as advantageous in the vehicle, the lifecycle of ethanol combustion includes some CO2 capture in the form of plants. I'm not sure about its efficiency for expansion work in internal combustion cylinders, but for electricity generation, methane combustion produced about half of the CO2 as coal combustion per megawatt hour of electricity generated. So, methane doesn't eliminate CO2, but it does reduce it when compared with coal. --OuroborosCobra (talk) 18:33, 30 March 2021 (UTC)

answering the "how reduced": The main way this is happening at the moment is to make the engine and car more efficient. Ways may be to ensure complete burning of fuel, use most efficient ignition (perhaps igniting in multiple places in the cylinder at the right time, or the center will be better than a spark at the edge), higher compression, less friction, lower mass in vehicle, better streamlining. Secondary ways could be using a hybrid car to recover breaking energy. Graeme Bartlett (talk) 21:53, 30 March 2021 (UTC)

Or, using non-combustion engines (i.e. electric vehicles) --Jayron32 11:34, 31 March 2021 (UTC)

Or, indeed, using an alternative source of fuel, as in hydrogen fuel cell vehicles. Rhythdybiau (talk) 17:45, 31 March 2021 (UTC)

You can't, as long as you burn a hydrocarbon fuel. That's why people want to get rid of combustion engines in many applications. Problem: for certain things, like aircraft, we don't have much to replace them at present. However, the thing about global warming is it's caused by us digging up hydrocarbons and burning it. Other fuel sources such as biofuels can be carbon-neutral: just cycling CO2 back and forth between atmosphere and fuel, adding no new carbon. --47.155.96.47 (talk) 22:40, 31 March 2021 (UTC)