Work done by an ideal gas at a constant volume is

For an exothermic reaction,

$A$ gas is allowed to expand against a constant external pressure of $2.5 \ bar$ from an initial volume of $2.5 \ L$ to a final volume of $4.5 \ L$. What is the amount of work done (in $J$)?

Consider the expansion given in problem $6.2$,for $1 \, mol$ of an ideal gas conducted reversibly.

The enthalpy of fusion of ice per mole is approximately $...$ $kJ / mol$.

$A$ perfect gas $(0.1 \ mol)$ having $\overline{C}_{v}=1.50 \ R$ (independent of temperature) undergoes the transformation shown in the graph from point $1$ to point $4$. If each step is reversible,the total work done $(w)$ while going from point $1$ to point $4$ is $(-)$ . . . . . . $J$ (nearest integer). [Given: $R=0.082 \ L \ atm \ K^{-1} \ mol^{-1}$,$1 \ L \ atm = 101.3 \ J$]