The first law of thermodynamics states that:

Write and explain the first law of thermodynamics.

$A$ gas is taken from state $A$ to state $B$ along two different paths $1$ and $2$. The heat absorbed and work done by the system along these two paths are $Q_1, Q_2$ and $W_1, W_2$ respectively. Then:

The heat supplied to a gas at a constant pressure of $5 \times 10^5 \ Pa$ is $1000 \ kJ$. If the volume of gas changes from $1 \ m^3$ to $2.5 \ m^3$,then the change in internal energy of the gas is (in $kJ$)

Density of water at $4 ^\circ C$ and $20 ^\circ C$ are $1000 \ kg/m^3$ and $998 \ kg/m^3$ respectively. The increase in internal energy of $4 \ kg$ water when it is heated from $4 ^\circ C$ to $20 ^\circ C$ is . . . . . . $J$. (Specific heat capacity of water $= 4.2 \ kJ/kg \cdot K$ and $1$ atmospheric pressure $= 10^5 \ Pa$)

The first law of thermodynamics confirms the law of . . . . . . .