Calculate H for the process in which Cl 2 (g) initially at 298.15 K at 1 bar

Calculate ΔH for the process in which Cl₂(g) initially at 298.15 K at 1 bar is heated to 690.K at 1 bar. Use the temperature-dependent heat capacities in the data tables. How large is the relative error if the molar heat capacity is assumed to be constant at its value of 298.15 K over the temperature interval?