For the reaction $PCl_{5(g)} \to PCl_{3(g)} + Cl_{2(g)}$,which of the following relations is correct?

An ideal gas is subjected to a cyclic process involving four thermodynamic states. The amounts of heat $(Q)$ and work $(W)$ involved in each of these processes are:
$Q_1 = 6000 \, J, Q_2 = -5500 \, J, Q_3 = -3000 \, J, Q_4 = 3500 \, J$
$W_1 = 2500 \, J, W_2 = -1000 \, J, W_3 = -1200 \, J, W_4 = x \, J$
The ratio of the net work done by the gas to the total heat absorbed by the gas is $\eta$. The values of $|x|$ and $\eta$ respectively are:

One mole of an ideal gas at $27^oC$ is allowed to expand reversibly and adiabatically. If the work done by the system is $3 \, kJ$,then the final temperature of the gas will be ......$K$. (Given: $C_v = 20 \, J/K \cdot mol$)

In an isothermal expansion,the increase in volume with a decrease in pressure of a gas is greater than in an adiabatic expansion,because .............

$A$ gas occupies $2 \ L$ at $S.T.P.$ It is supplied with $300 \ J$ of heat,causing its volume to expand to $2.5 \ L$ against an external pressure of $1 \ atm$. What is the change in internal energy in $J$?

If the heat of combustion of isobutane at constant volume is $Q_v$,what will be the heat of combustion of one mole of isobutane at constant pressure and standard conditions? (Given: $\Delta n_g = -3.5$)