Ants communicate with each other by depositing a chemical called pheromone on the substrate while they crawl forward. By this way, they follow their predecessor and large trail systems are built. Inspired by the communication via chemical signals of ants, we have proposed a model to investigate the collective motion in humans during an emergency. It is considered that pedestrians use some kind of virtual chemotaxis to find the shortest way to the exit. This basic idea is implemented with the floor field model which is the most popular cellular automata model. The dependence of the evacuation from a room on the virtual chemotaxis evaporating rate $f$ and the presence of the obstacle are investigated in this paper. The simulation results show that the increase in evaporation rate has been seen to slow down the evacuation. Moreover, it is found that positioning the obstacles in the room could lead to the phase transitions and decrease the evacuation time.