After a system is added 40-J heat, the system does 30-J work. How do you find the change of the system’s internal energy?

1 Answer
Mar 20, 2018

#10J#

Explanation:

1st Law of Thermodynamics:
#DeltaU=Q-W#
#DeltaU=# change in internal energy.
#Q=# Heat energy supplied .
#W=# work done by the system.

#DeltaU=40J-30J=10J#

Some physicist and engineers use different signs for #W#.

I believe this is the engineer's definition:
#DeltaU=Q+W# here, #W# is the work done on the system.
The system does work of #30J# hence the work done on the system is #-30J#.