Drag-and-dropping one image of a chemical is equivalent to adding one mole of a chemical into the reactor or receiver. The player can adjust coefficients in front of reactants and products by drag-and-dropping chemicals images into the reactor and receiver the required number of mes. All chemicals which are available for the player in the current level are shown in color, while those which are not available -in grayscale. Upon hoovering over the chemical, which is available for the player, a pop-up message appears (see the message for nitrogen dioxide in Figure ). It contains thermochemical data (Table ) and light absorp on proper es (Table ).