A sealed flask initially contains only and molecules
CHEMISTRY · Single correct · AP · Chemistry · Chemical Reactions · Chemical Reactions
Problem
A sealed flask initially contains only H2 and Cl2 molecules. After exposure to ultraviolet light, analysis shows that the flask now contains HCl molecules and fewer H2 and Cl2 molecules than before. Which evidence most directly justifies classifying the light-induced process as a chemical change?
(a) The total pressure in the flask decreased after irradiation, indicating that the gas particles slowed down.
(b) New covalent bonds between H and Cl atoms have formed, and original H–H and Cl–Cl bonds have been broken.
(c) The temperature of the gas increased after irradiation, showing that energy from the light was absorbed.
(d) The mass of gas in the sealed flask remained constant, demonstrating conservation of matter.