Question

Each line of the following table gives data for a process of a closed system. Each entry has the same energy unit. Determine the missing entries. Write down the procedure for each part.

Process	Q	W	E1	E2	Δ E
A	+50	?	-20	?	+70
B	?	+20	?	+50	+30
C	?	-60	+40	+60	?
D	-40	?	+50	?	0
E	+50	+150	?	-80	?

Answer 1

Process.A:

Apply energy balance,

$$ \begin{aligned} &Q=W+\Delta E \\ &50=W+70 \\ &W=-20 \end{aligned} $$

Find the value of \(E_{2}\).

$$ \begin{aligned} &\Delta E=E_{2}-E_{1} \\ &70=E_{2}-(-20) \\ &E_{1}=50 \end{aligned} $$

Process. B:

Apply energy balance,

$$ \begin{aligned} &Q=W+\Delta E \\ &Q=20+30 \\ &Q=50 \end{aligned} $$

Find the value of \(E_{1}\)

$$ \begin{aligned} &\Delta E=E_{2}-E_{1} \\ &30=50-E_{1} \\ &E_{1}=20 \end{aligned} $$

Process C

Find the value of \(\Delta E\).

$$ \begin{aligned} \Delta E &=E_{2}-E_{1} \\ &=60-40 \\ \Delta E &=20 \end{aligned} $$

Apply energy equation.

$$ \begin{aligned} &Q=W+\Delta E \\ &Q=-60+20 \\ &Q=-40 \end{aligned} $$

Process D:

Find the value of \(E_{2}\).

$$ \begin{aligned} &\Delta E=E_{2}-E_{1} \\ &0=E_{2}-50 \\ &E_{2}=50 \end{aligned} $$

A pply energy equation.

$$ \begin{aligned} &Q=W+\Delta E \\ &-40=W+0 \\ &W=-40 \end{aligned} $$

Process E:

Apply cnergy equation.

$$ \begin{aligned} &Q=W+\Delta E \\ &50=150+\Delta E \\ &\Delta E=-100 \end{aligned} $$

Find the value of \(E_{1}\).

$$ \begin{aligned} &\Delta E=E_{2}-E \\ &-100=-80-E_{1} \\ &E_{1}=20 \end{aligned} $$