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"A 100g mass is heated with a strong flame for 10 seconds then placed into a crucible on a heat proof mat. After cooling for 5 minutes the 100g mass is at 67.6C while the table it's resting on is at 24.2C. What will be the final temperature of the mass?"

Our teacher assigned us this problem to work on and its one I don't think is possible to solve without some extra information such as the heat capacities of both of the masses.

I tried adding both temps together and divided them to get the final temperature/average but I don't think that approach was going to be accurate. It takes different amounts of joules to increase the temperature of dissimilar materials, meaning if one loses a certain amount of joules the other will increase in temp but not by the same amount as the other substance(correct me if I'm wrong).

This is why I think the problem might need more information but when confronting my teacher with this she just said this in reply "Basically, the final temp of the mass will end up being the same temperature of the room. It will heat the room by a tiny, tiny, tiny quantity, but essentially end up at room temp."

Am I missing something here? This is my first thermodynamics orientated class so I'm not well versed. Thank you in advance.

Edit: here is the other information we are given:

The initial temp is 25.9C and the sample was at 180.2C after being heat up. The flame temp 190.5C. Conduction, convection, radiation are all involved.

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  • $\begingroup$ You don't know the initial temperature of the sample, and you don't know what form of heat transfer is involved (e.g., conduction, convection, radiation). A bunsen burner can heat the sample up to 1083 deg C, but the problem didn't tell you what type of flame was used. You need more information. $\endgroup$
    – David White
    Commented Aug 24, 2021 at 2:45
  • $\begingroup$ Sorry, that info is given I just didn't include it. The initial temp is 25.9C and the sample was at 180.2C after being heat up. Conduction, convection, radiation are all involved. Could I solve the problem with this info? $\endgroup$
    – import_hill
    Commented Aug 24, 2021 at 2:49
  • $\begingroup$ The initial temperature of what? The sample before it is heated up? Also note - conduction requires a thermal conductivity. Convection can be natural convection or forced convection, and is VERY dependent on the exact physical setup. Radiation is proportional to the forth power of the temperatures involved. You still need a LOT more data. $\endgroup$
    – David White
    Commented Aug 24, 2021 at 2:55
  • $\begingroup$ The sample before it is heated up. Conduction because the object is metal but we aren't given what type of metal. Convection from the bunsen burner. Radiation meaning the mass emits radiation after being heat up and dissipating into the environment. But why would you even need the type of heat transfer to calculate final temp, we already know it heat up to 180.2? $\endgroup$
    – import_hill
    Commented Aug 24, 2021 at 2:59
  • $\begingroup$ Are. you asked to find the final temperature, or the temperature after a specified amount of time? $\endgroup$
    – Chet Miller
    Commented Aug 24, 2021 at 3:08

1 Answer 1

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the crucial information is "After cooling for 5 minutes the 100g mass is at 67.6C while the table it's resting on is at 24.2C" since the table did noch change temperature in the first 5 minutes, why should it with smaller temperature difference in the next time. So you have to read the question very carefully, to look for the answer. So your teacher was right.

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  • $\begingroup$ The mass will cool to the temperature of the room, but it may take more than 5 min. $\endgroup$
    – R.W. Bird
    Commented Aug 24, 2021 at 14:44
  • $\begingroup$ @ R-W.Bird: "may take more than 5 minutea" ? It is stated in the text that it takes more time, so what shall this coment say? $\endgroup$
    – trula
    Commented Aug 24, 2021 at 20:06
  • $\begingroup$ You are right, my mistake. $\endgroup$
    – R.W. Bird
    Commented Aug 25, 2021 at 13:55

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