$(\Delta H - \Delta U)$ for the formation of carbon monoxide $(CO)$ from its elements at $298 \ K$ is ............. $J \ mol^{-1}$. $(R = 8.314 \ J \ K^{-1} \ mol^{-1})$

Express the change in internal energy of a system when
$(i)$ No heat is absorbed by the system from the surroundings,but work $(w)$ is done on the system. What type of wall does the system have?
$(ii)$ No work is done on the system,but $q$ amount of heat is taken out from the system and given to the surroundings. What type of wall does the system have?
$(iii)$ $w$ amount of work is done by the system and $q$ amount of heat is supplied to the system. What type of system would it be?

When one mole of $NH_3$ gas and one mole of $HCl$ gas are mixed in a closed container to form ammonium chloride gas,which of the following is true?

$A$ sample of liquid in a thermally insulated container (a calorimeter) is stirred for $2 \ hr$ by a mechanical linkage to a motor in the surroundings. For this process:

The heat change for the following reaction at $298 \ K$ and at constant pressure is $+7.3 \ kcal$: $A_2B_{(s)} \to 2A_{(s)} + 1/2B_{2(g)}$,$\Delta H = +7.3 \ kcal$. The heat change at constant volume would be:

$2.5 \ kJ$ of work is done on the system and it releases $1500 \ J$ of heat. What is the change in internal energy (in $J$)?