The change in thermal (internal) energy when a substance is heated or cooled is found from three things. The equation is: change in thermal energy (J) = mass (kg) × specific heat capacity (J/kg°C) × change in temperature (°C).
A bigger mass needs more energy for the same temperature rise, and so does a bigger temperature change. The mass must be in kilograms. For example, heating 2 kg of aluminium, with specific heat capacity 900 J/kg°C, by 10 °C needs 2 × 900 × 10 = 18 000 J.
Water has a specific heat capacity of 4200 J/kg°C. Warming 0.5 kg of water by 20 °C needs 0.5 × 4200 × 20 = 42 000 J. A 3 kg block with specific heat capacity 500 J/kg°C heated from 20 °C to 30 °C has a temperature change of 10 °C, so it gains 3 × 500 × 10 = 15 000 J. A 0.2 kg copper block (specific heat capacity 400 J/kg°C) warmed by 50 °C gains 0.2 × 400 × 50 = 4000 J.