This can be calculated using the equation q = mcΔT where m is the mass of iron, c is its specific heat capacity and ΔT is the change in temperature.
Assuming c does not change with temperature and has a value of: c = 0.444 J/K mol, the q can be calculated as: q = 20.0 g * 0.444 J/K mol * 25 K = 222 J (Note: K refers to Kelvin which equals ˚C + 273, therefore ΔT is the same in K as it is in ˚C.)
