What is the change in internal energy and work to be done in the following case:1. A gas expands when 849 J of energy is added to it by heat. The ...

According to the law of conservation of energy the total
energy in a system is constant. Any work done to introduce energy into the system
increases the potential energy of the system and any work done in a process that expels
energy out of the system decreases the internal energy in the
system.

1. Here we have 849 J of energy added to the gas in
the form of heat. This makes the gas expand and it does 702 J of work on its
surroundings. The change in the internal energy is the difference 849 - 702 = 147
J

The internal energy of the gas increases by 147
J

2. When the gas does work equal to 890.6 J, the same
amount of energy must be added to it, else there will be a fall in the internal
energy.

To keep the internal energy at the end of the
process the same as the internal energy at the start of the process 890.6 J of energy
has to be added.