The internal energy change for a system is + 20 Cal and the work done is – 200 Cal. Find the heat exchanged between the system and the surrounding.

CONCEPT:

• The first law of thermodynamics is a restatement of the law of conservation of energy. It states that energy cannot be created or destroyed in an isolated system; energy can only be transferred or changed from one form to another.
• When heat energy is supplied to a thermodynamic system or any machine:  Two things may occur:
  • The internal energy of the System or machine may change.
  • The system may do some external work.

According to the first law of Thermodynamics:

ΔQ = ΔW + ΔU

Where ΔQ = Heat supplied to the system, ΔW = work done by the system, and ΔU = change in internal energy of the system 

EXPLANATION:

Given that:

ΔW = - 200 Cal and ΔU = + 20 Cal

According to the first law of Thermodynamics:

Heat exchanged (ΔQ) = ΔW + ΔU = - 200 + 20 = - 180 Cal