Outflows generated by protostars heavily affect the kinematics and chemistry of the hosting molecular cloud due to strong shocks. These shocks heat and compress the ambient dense gas switching on a complex chemistry that leads to an enhancement of the abundance of several species, as reported in "chemically active" outflows, whose archetype is the outflow of the low-mass Class 0 protostar L1157. I'll present the results of the spectral survey of the shock region L1157-B1 carried out with PACS, SPIRE, and HIFI instruments on board Herschel in the framework of Herschel key program CHESS. The high spectral resolution data from HIFI show that different excitation conditions coexist in the B1 shock while the high spatial resolution of PACS data shows a different spatial distribution of the the detected species. We will discuss the properties of the different gas components and present the physical conditions derived from different species. We will present a first comparison with shock models highlighting the complex structure of this shocked region.