Question

State first law of thermodynamics. what conclusions do you draw from it (a) for an isothermal process (b) for an adiabatic process

Answer 1

First law of Thermodynamics states that      
                                            "Energy can neither created nor destroyed. It can simply transform from one form to the other"

For example:                       
 A microwave transforms electrical energy into thermal energy.
 During photosynthesis, light energy is converted into chemical energy.

In the isothermal process, the temperature remains constant.  According to the first law, internal energy is directly proportional to temperature.  If work is done inside the system, heat flows outside. If work is done outside, heat flows inside.

In an adiabatic process, heat is neither added nor removed from a system. According to the first law, internal energy is equal to negative work done and inversely proportional to temperature.

Answer 2

The first Law of Thermodynamics States that,

Total Energy of an isolated system is constant, energy can be transformed from one form to another, but can neither be created nor be destroyed. It is formulated as
 Change in U = Q - W
 where
 U =  internal energy
Q = Heat
W =  Worl Done 

a) for an isothermal Process

Change in U = 0
So 
Q = W

b) for adiabatic process

Q = 0 
So
Change in U = - W