Important brain needed:) aluminum rods expirement


by 14mflohr
Tags: chemistry
14mflohr
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#1
Jun6-12, 05:23 PM
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Does the insertion of aluminum rods into a beaker of water affect the time it takes for the temperature of the water to reach 75 degrees Celsius when heated?

I believe it would because there is more mass but I'm not sure and I don't know why (as in the law of equation to verify this.)

Could someone please tell me whether it would or not and how to prove it?

Thank you so much!!! :)

I would guess that the more mass of aluminum you put in the longer it will take to reach 75 degrees because of the amount of energy needed of something like that.. maybe the equation QΔ= M(TΔ)Cp <-- maybe
PLEASE HELP
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HallsofIvy
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#2
Jun6-12, 05:31 PM
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What happens is that when you insert the aluminum rods both the water and the aluminum. And it is not just a matter of "mass". Water and aluminum have different "heat capacities", the energy necessary to raise the temperature 1 degree C.
As you can see here: http://www.iun.edu/~cpanhd/C101webno...cificheat.html
Water has a heat capacity of approximately 4.2 Joules per gram per degree and aluminum has a heat capacity of approximately .9 J per gram per degree.
14mflohr
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Jun6-12, 05:38 PM
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Thanks:) also though if I put an aluminum rod into a beaker of water then heat the beaker will it take longer for the water to reach 75 celsius because they have different heat capacities. Will the aluminum use up energy that would otherwise be used to heat the water?

14mflohr
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#4
Jun6-12, 05:50 PM
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Important brain needed:) aluminum rods expirement


If I put an aluminum rod into a beaker of water then heat the beaker on a hot plate, will it take longer for the water to reach 75 celsius compared to when it is heated alone? Someone helped me by saying that they have different heat capacities. Will it take longer for the water to reach 75 degrees celsius if the aluminum rod is inside? Would the aluminum use up energy that would otherwise be used to heat the water? Please explain and give me an equation or law of sorts to explain to others:)
thanks!!!
DaveC426913
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#5
Jun6-12, 06:00 PM
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What do you think? We cannot answer your question until you have tried to answer it yourself.
14mflohr
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#6
Jun6-12, 06:13 PM
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I believe it would because the aluminum and water will both draw from the heat source. Aluminum needs approximately 0.9 joules of energy to raise one degree and water needs 4.79 joules. Because of this the aluminum rod and water will have different final temperatures. The tests that I did suggest that the aluminum rods do use a fraction of the heat source. What I don't know how to do is to figure out what percentage of the energy the aluminum uses, or what equation to use. I thought that maybe surface area is a part of it considering the aluminum rods only touch a small section of the beaker that's being heated while the water is touching much more. I don't need anyone to do the equations for me if they don't want to or aren't allowed, I'm just asking for some help in which direction I should proceed.
14mflohr
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Jun6-12, 06:52 PM
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anyoneeee??? :P
DaveC426913
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Jun6-12, 06:52 PM
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You should probably ignore the configuration of the rod and beaker, and consider it simply an idealized setup. Also, assume the water and rod have enough time to reach equilibrium with each other (i.e. they are the same temp)

Think about how long it would take warm up a gallon of water. Then think of how long it would take to warm up a gallon of aluminum rod. Consider the specific heat of each.

If the beaker were completely full of the aluminum rod, would it heat up faster or slower than if it were full of water?
DaveC426913
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#9
Jun6-12, 06:57 PM
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Did not realize this was a dupe post.
berkeman
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Jun6-12, 07:09 PM
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Quote Quote by 14mflohr View Post
If I put an aluminum rod into a beaker of water then heat the beaker on a hot plate, will it take longer for the water to reach 75 celsius compared to when it is heated alone? Someone helped me by saying that they have different heat capacities. Will it take longer for the water to reach 75 degrees celsius if the aluminum rod is inside? Would the aluminum use up energy that would otherwise be used to heat the water? Please explain and give me an equation or law of sorts to explain to others:)
thanks!!!
Welcome to the PF. Please do not multiple post your question. I have merged two of your three threads.
chemisttree
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Jun7-12, 10:24 PM
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Quote Quote by 14mflohr View Post
anyoneeee??? :P
You haven't given us enough information to answer the question. Are you simply inserting aluminum rods into the water? Do you remove exactly the same volume of water that the aluminum rods displace? Are the rods completely submerged or are their ends hanging out like a heat exchanger?

Details! DETAILS!


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