You will need to supply 4.8 GJ of heat energy.
The equation for the reaction is
"CaCO"_3 → "CaO" + "CO"_2CaCO3→CaO+CO2; Δ_rH = "+179 kJ"//"mol"
Step 1. Convert the mass of "CaCO"_3 to moles.
2.7 × 10^3 color(red)(cancel(color(black)("kg CaCO"_3))) × ("1 kmol CaCO"_3)/(100.09 color(red)(cancel(color(black)("kg CaCO"_3)))) = "27.0 kmol CaCO"_3
Step 2. Calculate the amount of heat required.
27.0 color(red)(cancel(color(black)("kmol CaCO"_3))) × "179 MJ"/(1 color(red)(cancel(color(black)("kmol CaCO"3)))) = "4800 MJ" = "4.8 GJ"