A charged cell phone has chemical energy stored in its battery. As you use your phone, the amount of chemical energy in the battery decreases. Why is this not a violation of the first law of thermodynamics?

Because the chemical energy is converted to electrical enegy in the cell phone

Explanation:

This set up is not a voilation of the first law of thermodynamics because the chemical energy is not lost, it is only being transformed into electrical energy.

According to the first law of thermodynamics "energy is neither created nor destroyed but transformed from one form to another".

there are no contact forces mentioned on the list of choices that you've provided.