First Law of Thermodynamics

Objects in Contact with one another have the same temperature if they are in thermal equilibrium. Nothing else matters

E= final thermal energy

initial thermal energy - work= E_i - W= E_f

E_f- E_i= -W

Thermal energy decreases when work is done by a system

Thermal energy increases when work is done on a system

Conservation law

change in thermal energy= heat -work

 $\Delta E=Q-W$  

Heat gained by a system adds thermal energy

Work done by a system takes away thermal energy

a) Make sure you use correct signs here it all starts by defining the system

b) what are we looking for? rearrange our 1st law to solve for it.