With increase in temperature, the internal energy of a substance

$$dU = CvdT - \left[ {P + T\left( {\frac{{\left( {\frac{{\partial V}}{{\partial T}}} \right)p}}{{\left( {\frac{{\partial V}}{{\partial P}}} \right)T}}} \right)dV} \right]$$
SO, we can say on increasing the temperature the internal energy changes increases physically also when we give heat to a system some of the heat is used for raising the thermal energy of the system and doing some work by the system.