Energy can be transferred from a system to the surroundings as work if $.....$

$A$ 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 $J$)?

If $5 \ mol$ of an ideal gas expands from $10 \ L$ to a volume of $100 \ L$ at $300 \ K$ under isothermal and reversible conditions,then the work done,$w$,is $-x \ J$. The value of $x$ is $ . . . . . . $. (Given $R = 8.314 \ J \ K^{-1} \ mol^{-1}$)

Assertion : During an adiabatic process,heat energy is not exchanged between the system and its surroundings.
Reason : The temperature of a gas increases when it undergoes an adiabatic expansion.

Assertion : Absolute values of internal energy of substances cannot be determined.
Reason : It is impossible to determine exact values of constituent energies of the substances.

For a chemical reaction,when does $\Delta H = \Delta U$ occur?