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..
In: 14
“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.
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.
‘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.
> 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
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.
Did you use the flame to heat up a certain volume of water to determine how many calories it was? The energy loss would be not all the energy went into heating up the water so you can’t precisely tell how many calories are in the thing you burned.
Latest Answers