Submitted by bigmacqween t3_yiecoa in explainlikeimfive
What is the terms for it? We did a lab where we burned food objects, it asked if there were any energy losses in the experiment. I searched google but couldn’t find anything I understood, can someone please help me understand? We used an open flame to burn foods such as nuts, beans, marshmallows..
Just to add to this, when you hear people talking about "energy loss", what they are actually talking about is the loss of useful energy.
With the burning stuff as an example they might be talking about the amount of energy "lost" by making light when what they wanted was just heat.
Also defined as entropy.
I understand that matter cannot b created or destroyed. I’m just wondering if it’s just that simple? Like the term “by burning the food, some of the energy from the food particles was lost by burning the food, and turning to gas, affecting the weight of the food “
All you need to understand is that in different environments matter behaves differently.
This forms a complex web of rules we call chemistry. I do not know half of the rules, and don’t enjoy studying it, but it’s essentially a study of how these base particles can build up to form these complex geometric patterns and small forces that always want to try and follow these rules.
Pressure, temperature, mass, composition, scale, molecular structure, atomic structure, and loads of other shit all affect these rules. Like, Oxygen at x temperature will want to turn to liquid. Oxygen at x temperature will turn gas. Oxygen at x pressure will want to be liquid. Well, it gets more complicated when they interact with eachother, as temperature and pressure are related. This gets even more complicated once you factor in that you aren’t just dealing with one type of element, and that elements also have rules with how they interact with eachother. Ex:Oxygen at x temperature and hydrogen at x temperature bond together to form water, which also does different things at different temperatures.
This can get insanely complex insanely fast. But the rules all must be followed. Sometimes this sets up a row of dominoes than can get knocked over because all of the rules line up in a way that cause a lot of this matter/bond stored energy to be released.
By exposing heat to this food, you can start a reaction that sustains itself like wood on fire.
Once you get that initial starting flame to burn, and as long as you keep giving enough molecules to burn, the wood at certain temperature pulls oxygen apart to create a different compound which is a little chemical reaction. A lot of times there are many chemical compounds created as it’s not easy to get a completely pure molecular compound. Smoke, ash, infrared heat, all of it is dispersed.
The overall governing rules that explain these things are the Laws of Thermodynamics, like conservation of energy. If you want to understand this better, spend time focusing on videos explaining chemical reactions and the laws of thermodynamics. Those are your googleable terms.
Food particles is a fairly unhelpful way to look at calorimetry. If you look at respiration or combustion the products are chemically more stable than the reactants. Carbon dioxide (gas) has stronger chemical bonds than sugar (solid). A house of cards is less stable than a collapsed pile of cards. Heat energy is released in both cases when they change.
So yes and no to it being that simple. For understandings sake, you can say that it is that simple, you burn the food, some energy is lost from the food as it turns into energy/matter in other forms(matter and energy can be converted to each other), the total amount of energy never changes, only where and how its stored. On the other end of the complexity spectrum, what actually is happening when you burn that food, is alot more meticulous, for anyone's liking, even the people who study things like molecular physics lol.
Also defined as entropy.
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> it asked if there were any energy losses in the experiment.
No, when you burn something, no energy is lost. There is a fixed amount of energy in the universe and we cannot create or destroy energy. All we can do is transform it from one form to another.
When people say energy is "lost", it is the imperfect transformation of energy from one for to the other. If you turn mechanical energy into electrical energy (via an alternator or something) it's not a 100% conversion. You will turn 90% of the mechanical energy into electrical energy, and 10% of the energy into heat energy. The amount of energy is constant and unchanged, but the transformation from one form to the other is less than 100% efficient
When you burn something, no energy is lost. You are just converting matter (which is just bound up energy) into light energy, heat energy, and a different kind of matter (smoke and ash). The same amount of energy exists in the universe before you burned the thing and after
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It's been a while since I studied these things, but I'll do my best. As others have said, energy is always conserved, so when we talk about energy loss we really mean "how much energy went places where we didn't intend."
The biggest one in the case of an open fire is going to be "waste heat." If you're heating a pot of water over the fire, the smoke and hot air that has already passed your water is still very hot, much hotter than the water itself. Because that air is still hot, it's carrying energy that could have gone into your food but it escaped into the surrounding room instead. With perfect energy transfer, the hot air would lose its heat to the water, and it would be the same temperature as the water by it time floats away into the room.
The next biggest source would be "incomplete combustion." An ideal fire would burn all of your fuel and food sample until it's nothing but CO2 and water. You probably saw some smoke rising off of the flame. Smoke is visible because it's little flakes and molecules of unburnt stuff, which was carried away from the fire before it could burn. That stuff had energy which didn't get released in the burning process, instead the energy was carried into the surroundings.
Another issue is moisture in your fuel (or the food you're burning). Props to /u/robot_egg for bringing this idea up. They did a great job explaining, so I'll just point out that it's usually very complicated to know how much water is in your fuel or food sample. When that water is boiled out by the fire it turns to a gas, which absorbs an amount of energy known as the "heat of vaporization." The only way to get that energy back is to condense the water vapor back to a liquid. Since that's not going to happen in your open fire situation this energy can be considered lost because the water vapor escaped. Your dried nuts and beans probably have very little water. A quick google suggests marshmallows are something like 20% water, so that's a significant issue there unless you dried the marshmallows first.
A really minor part of your losses would have been "radiant energy." The fire gives off light and light is a form of energy. To return to the idea of heating a pot of water, this light from the fire is going places other than the pot of water so again its being 'lost' because it isn't doing the job you care about. The amount of light is very small compared to the heat of the flame, so this is going to be a insignificant amount of lost energy, but I'm including it to be as thorough as possible.
'Energy loss' has little meaning unless you were trying to do something with that energy.
A useful context would be in something like a car engine. Some of the energy from the fuel is lost via (for example) heat escaping from the cylinders and the engine, instead of propelling the car.
So if you were burning food to heat the room, light would be lost energy. If you were burning food to light the room, heat would be lost energy.
But if you were burning food for no particular reason (beyond 'experiment') the question is pretty meaningless, unless the intended answer is something along the lines of, 'energy is never lost to the universe, it just changes form'.
I think you're talking about energy you weren't able to measure in an experiment. For your example, the smoke coming off of the burning food was energy escaping that you might not have been measuring. I'm also not an expert on chemistry, but the reactions may have produced chemical energy, where some of the energy was used to synthesize chemicals and is stored in their bonds (not measurable via heat.)
If I'm following the logic properly, you're trying to figure out why your measured energy didn't add up to the calculations you did to predict it, and where that energy went.
I suspect they're referring to the heat of vaporization of water in the food. It takes a lot of energy to evaporate water. Now, this energy isn't "lost", but it does affect how much temperature rise you will observe.
When burning food samples to determine their caloric content, you'd normally carefully dry the food to avoid this effect.
Ahhh, I see. Thank you so much for the insight. This helped
RamTheKnife t1_iui6pfl wrote
"Energy loss" does not exist. The law of conservation of energy states that energy cannot be created or destroyed only converted from one form to another. So when you burn the food, some of the chemical energy stored in the food item is converted into the byproducts of the burning, like smoke and heat etc.