You need to measure the temperature to get the temperature rise when the reaction has completed then you can put it in the equation q = mcΔt

so m is the mass of a substance in which the heat is being transferred.

so c is the specific heat capacity (which is 4.2 in this case)

so Δt is the temperature rise

and q is the heat energy given out/released

so q = 100*4.2*54.2

so q = 22764 KJ

Is this right? I think I was getting confused with the 0.4g of fuel as the next part is calculating moles!

You get the mass right now. But there's another problem. The specific heat capacity(c) that you are using is 4.2

**J**/g/°C, note the unit. So,

~~why are you using kJ as your unit in the calculation?~~ what shall you do so as to use the unit kJ as required in the question?

Once you handled this, you can go to the next part.

Edit: I overlooked the original question that told us to use kJ as the energy unit.