Draw a p-V diagram and explain the concept of positive and negative work. Give one example each.

A gas contained in a cylinder fitted with a frictionless piston expands against a constant external pressure of $1 \mathrm{atm}$ from a volume of

$5 \mathrm{L}$ to a volume of $10 \mathrm{L}$. In doing so it absorbs $400 \mathrm{J}$ of thermal energy from its surroundings. Determine the change in internal energy of system.

An ideal gas is taken through an isothermal process. If it does $2000\mathrm{J}$ of work on its environment, how much heat is added to it?

A hypothetical thermodynamic cycle is shown in the figure. Calculate the work done in 25 cycles.