Formula: First Law of Thermodynamics Internal energy Thermal energy Work

$$\Delta U ~=~ \class{gold}{\Delta Q} ~+~ \class{purple}{\Delta W}$$ $$\Delta U ~=~ \class{gold}{\Delta Q} ~+~ \class{purple}{\Delta W}$$ $$\class{gold}{\Delta Q} ~=~ \Delta U ~-~ \class{purple}{\Delta W}$$ $$\class{purple}{\Delta W} ~=~ \Delta U ~-~ \class{gold}{\Delta Q}$$

Rearrange formula

Internal energy

$$ \Delta U $$ Unit $$ \mathrm{J} $$

Change of internal energy $\Delta U=U_2-U_1 $ of a system (e.g. a gas) is the sum of the amount of heat $Q$ and the work $W$ done.

Thermal energy

$$ \class{gold}{\Delta Q} $$ Unit $$ \mathrm{J} $$

Thermal energy (heat) added to the system ($\class{orange}{\Delta Q}>0$) or released from the system ($ \class{orange}{\Delta Q}< 0 $).

Work

$$ \class{purple}{\Delta W} $$ Unit $$ \mathrm{J} $$

Work done ON the system ($ \class{purple}{\Delta W} > 0$) or work done BY the system ($\class{purple}{\Delta W} < 0$).