What is the energy equivalent of 5.0kg of mass?

Ah hah !  Sounds to me like an  " E = m c² "  question.

c = 3 x 10⁶  m/s

c² = 9 x 10¹² m²/s²

                       E  =  (5 kg)  x  (9 x 10¹² m²/s²)

                           =       45 x 10¹²  kg-m²/s²

                           =       4.5 x 10¹³  newton-m

                           =        4.5 x 10¹³ Joules  . 

That's the energy needed to

-- run a 1000-watt blow-dryer for roughly  1,427 years .
or
-- run a 400-horsepower truck, wide open, pedal to the metal,
   for   4.78 years .