The cooler will fit, but it might not be sufficient to cool the i5 2400. The lower end chips with lower TDPs tend to get cheaper stock coolers designed around the lower TDP. For Sandy Bridge chips, the stock i5 cooler would have a copper slug in it, while the Pentium cooler would be aluminum only. The aluminum only Pentium cooler might not be sufficient to keep the i5 2400 cool under full load conditions.