In which ways the internal energy of a system can be changed?

What happens to the internal energy of a system if:
(i) Work is done on the system
(ii) Work is done by the sytem?

Why internal energy is a state function but is not work?

What is the relationship between internal energy change and enthalpy change?

26.

What is heat(q)?

What is the unit for work in S.I. system?

For the same increase in volume, why work done is more if the gas is allowed to expand reversibly at higher temperature?

Define the law of conservation of energy.