25 kJ is already energy.

Do you need to convert 25 kJ to J?

If so, you need to know that the prefix 'k' means times 1000.

Hence 1 km = 1000 m

Similarly, 25 kJ = 25 000 J.

If you want to convert kilojoules to other units of work or energy (such as watt-hours, horsepower-hours, BTUs, calories, etc), here's a handy web to use:

http://www.unitconversion.org/unit_converter/energy.html