Two copper blocks, each of mass 5.0 kg, one at 80 C and the other at 10 C are pl

Question

Two copper blocks, each of mass 5.0 kg, one at 80 C and the other at 10 C are placed in contact in an isolated container. The specific heat capacity of for copper for 0.385 J/ K*g and maybe assumed constant over the temperature from 0 C to 100 C. First estimate the sign of (delta)H hot, (delta) H cold, (delta) H total, (delta) S hot, (delta)S cold, (delta) S total, respectively, and then determine the numerical values for them the subscript hot, cold, and total stands for the hot brick, the cold brick and the sum of the two.

Explanation / Answer

The total ?H for the system will be zero as it is isolated. It is evident that the final temperature is going to be 50 degrees for each block, due to symmetry (both the blocks exchange energy worth 50 degrees) The ?H for each of the block is the change in heat. This is =m*c*?T =10*0.385*(100-50) = 192.5 Joules (For each block) The ?S is given as: dS = dH/T = m*c*dT/T Integrate both sides ?S = m*c*ln (T2/T1) Here T2 is the final temperature and T1 is the initial temperature ?S = m*c*ln (323/373) + m*c*ln (323/273) ?S = 10*0.385 * ln (1.02455096) ?S = 0.0933795509 Joule/Kelvin This is positive indicating that the reaction is spontaneous

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