This study is concerned with the effects of computer simulations of two novel chemistry problems on the problem solving ability of students. A control-experimental group, equalized by pair groups (n[subscript Exp] = n[subscript Ctrl] = 78), research design was used. The students had no previous experience of chemical practical work. Student progress was checked twice, once 15 minutes after they had started looking for a solution, before the experimental group was exposed to the simulation, and again after completion of the test. The 15 minutes check confirmed the equivalence of the two groups. The findings both verified the difficulty of the problems, and indicated improved mean achievement of the experimental group (students who were shown the problem simulations), in comparison to the control group (students who solved the problem in the traditional way). Most students assumed that the major benefit of the simulations was to help them with the proper application of the equations. The effects of scientific reasoning/developmental level and of disembedding ability were also examined. The performance level for formal reasoners was found to be higher than that for transitional reasoners and that for transitional reasoners higher than for concrete ones. Field independent students were found to outperform field intermediate ones, and field intermediate students were found to outperform field dependent ones. Finally, in most cases the experimental group outperformed the control group at all levels of the above two cognitive factors.