The air in an inflated balloon (defined as the system) is warmed over a toaster and absorbs 130 J of heat. As it expands, it does 79 kJ of work. What is the change in internal energy for the system? Express the energy in kilojoules to two significant figures.

The change in internal energy for the system = - 78.87 KJ = - 79 KJ to 2 s.f

Explanation:

The first law of thermodynamics states that energy can neither be created nor destroyed but can only be transformed from one form to another.

It goes further to explain that change in the internal energy of a system (ΔU) is the sum of heat exchanged (Q) and the work done (W) by the system or on the system.

If work is done by the system, sign of work is ‘-’, if work is done on the system, the sign of work is ‘+’.

If heat is released by the system, the sign of q is ‘-’. And if heat is gained by the system, then the sign of q is ‘+’.

ΔU = Q + W

Q = 130 J

W = - 79 KJ = - 79000 J

ΔU = 130 - 79000 = - 78870 J = - 78.87 KJ = - 79 KJ

true tan speed = ang vel x radius