Steven W. answered • 07/14/16
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I think the other solution may be incomplete, because the 20.8 J/(mol K) is actually specific heat capacity, so that 1144 J is the heat required to change 1 mol by 55 K. To get the total amount of heat to change all the 250 g by 55 K, I think you also have to calculate the number of moles and multiply the 1144 number by that number. You have enough information to do that.
Steven W.
tutor
Yes I get that. These homework websites can be finicky, and if it wants two sig figs, you may just need to truncate it to 71,000. But, with the information given, I think that answer is correct.
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07/14/16
Lara N.
How do I know it isn't negative??
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07/14/16
Steven W.
tutor
The general formula for heat transfer without a phase change is:
q = mcΔT
So q will be negative only if the temperature is lowered. Negative q corresponds to heat leaving the system.
When I looked at the phrasing again, it did say the system experiences an "evolution" of heat, which seems to suggest that heat is leaving the system. So you may be correct, that the "evolved" heat should be listed as negative. It is worth a try.
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07/14/16
Lara N.
07/14/16