The diagram shows a cross-section of a thermos. The vacuum between the outer and inner bottles is a space containing no air or other matter. Which statement best describes the purpose of the vacuum inside a thermos.

What can be added to the examples section of each circle? endothermic: ice melting into water, and a heat pack becoming warm exothermic: a glow stick glowing, and fireworks exploding endothermic: ice melting into water, and an instant ice pack turning cold exothermic: fireworks exploding, and gasoline burning endothermic: a glow stick glowing, and a heat pack becoming warm exothermic: an instant ice pack turning cold, and ice melting into water endothermic: gasoline burning, and an instant ice pack turning cold exothermic: ice melting into water, and an instant ice pack turning cold

Calculate the molar mass of aluminum oxide (al2o3). express your answer to four significant figures.

Two nitro no2 groups are chemically bonded to a patch of surface. they can't move to another location on the surface, but they can rotate (see sketch at right). it turns out that the amount of rotational kinetic energy each no2 group can have is required to be a multiple of ε, where =ε×1.010−24 j. in other words, each no2 group could have ε of rotational kinetic energy, or 2ε, or 3ε, and so forth — but it cannot have just any old amount of rotational kinetic energy. suppose the total rotational kinetic energy in this system is initially known to be 32ε. then, some heat is removed from the system, and the total rotational kinetic energy falls to 18ε. calculate the change in entropy. round your answer to 3 significant digits, and be sure it has the correct unit symbol.