Consider a glass beaker that contains an unidentified clear colorless liquid. If

Question

Consider a glass beaker that contains an unidentified clear colorless liquid. If the liquid sample is vaporized (process 1) and then allowed to condense back to a liquid (process 2), which of the following descriptions of the processes is correct? Process 1 is exothermic and process 2 is endothermic Process 1 is exothermic and process 2 is endothermic Process 1 is exothermic and process 2 is endothermic Process 1 is exothermic and process 2 is endothermic If the sample releases 55 kJ of heat and simultaneously does 39 kJ of work, what can we say about the change in energy of the sample? delta E > 0 delta E

Explanation / Answer

(3) during the conversion of liquid into a vapour some amount of heat must be absorbed so the process is endothermic.

During the condesation heat is released so the process is exothermic reaction.

Therefore option B is correct

(4) Give work done by the system , W = +39 kJ

   Amount of heat released , q = -55 kJ

From first law of thermodynamics , q = dE + W

                                         so dE = q - W

                                                 = -55 -(+39) kJ

                                                 = -94 kJ

                                             dE < 0

Therefore option (b) is correct

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