Question

(a) Calculate ∆H and ∆S, the enthalpy and entropy changes, respectively,
when one mole of copper (initially at 500 K) is brought into thermal equi-
librium with a thermal reservoir at 400 K. Consider one mole of copper
and the thermal reservoir to form an isolated system. [Hints: 1. Thermal
reservoirs are chambers which are always maintained at the same temper-
ature irrespective of the temperatures of the objects in contact with it, 2.
S is an extensive state function.]
(b) Comment whether the process is reversible or irreversible.

Answer 1

Answer

a) enthalpy change (ΔH) as the heat of a process when pressure is held constant: ΔH ≡ q at constant pressure. The letter H stands for “enthalpy,” a kind of energy, while the Δ implies a change in the quantity.

$\Delta H=nC_pdT=1\times0.385\times100$

$=38.5J$

Now change in entropy

$\Delta S=\frac{\Delta H}{T}=\frac{38.5}{500}=0.77$ J/k

b) this above process is reversible.