A system does 213 J of work on its environment and gains 77.8 J of heat in the process. Find the change in the internal energy of (a) the system and (b) the environment.

a) Change in internal energy of the system = - 135.2 J

b) Change in internal energy of the environment = 135.2 J

Explanation:

From the mathematical statement of the first law of thermodynamics,

ΔU = Q - W

ΔU = Change in internal energy of the system = ?

Q = heat transferred into or out of the system. For this system, heat is transferred into it, Q = 77.8 J

W = workdone = 213 J (positive because work is done by the system on the environment)

ΔU = 77.8 - 213 = - 135.2 J

The change in internal energy of the environment is just the negative of that of the system. The balance is always so.

Hence, change in internal energy of the environment = -(- 135.2) = 135.2 J

it is the minimum amount of material needed to sustain a fission reaction.

critical mass is the minimum amount of fissionable material that must be assembled for a sustained fission reaction to take place. although two to three neutrons are produced for every fission, not all of these neutrons are available for continuing the fission reaction. if the conditions are such that the neutrons are lost at a faster rate than they are formed by fission, the chain reaction will not be self-sustaining.   at the point where the chain reaction can become self-sustaining, this is referred to as critical mass.