$A$ gas expands isothermally from $10 \, dm^3$ to $20 \, dm^3$ at a constant external pressure of $1 \, atm$. If it absorbs $800 \, J$ of heat from the surroundings,what is the value of $\Delta U$ in $J$ for this process?

For water $\Delta_{vap} H = 41 \ kJ \ mol^{-1}$ at $373 \ K$ and $1 \ bar$ pressure. Assuming that water vapour is an ideal gas that occupies a much larger volume than liquid water,the internal energy change during evaporation of water is $...... \ kJ \ mol^{-1}$.
[Use: $R = 8.3 \ J \ mol^{-1} \ K^{-1}$]

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:

The first law of thermodynamics is only:

If $2 \ kJ$ of heat is released from the system and $6 \ kJ$ of work is done on the system,what is the internal energy change $(\Delta U)$ of the system?

For the $1^{st}$ law of thermodynamics,select the correct option.