$A$ system receives $100 \ cal$ of heat,and at the same time,$50 \ cal$ of work is done by the system. Calculate the change in internal energy. (in $cal$)

Based on the first law of thermodynamics,which one of the following is correct?

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?

$A$ mixture of $2 \ mol$ of $CO_{(g)}$ and $1 \ mol$ of $O_{2(g)}$ is ignited to convert $CO$ to $CO_2$. Which of the following relations is correct?

For the reaction $C_{(s)} + \frac{1}{2}O_{2(g)} \to CO_{(g)}$ at constant $T$ and $P$,which of the following statements is correct?

$\Delta_{vap} H^{\ominus}$ for water is $+40.49 \ kJ \ mol^{-1}$ at $1 \ bar$ and $100^{\circ} C$. The change in internal energy for this vaporization under the same conditions is . . . . . . . . . . $kJ \ mol^{-1}$. (Given $R = 8.3 \ J \ K^{-1} \ mol^{-1}$)