Calculate the partial pressure, in atmospheres, of o2 in the dry air outside an airliner cruising at an altitude of about 20000 ft (6096 m), where the atmoshperic pressure is 351 mm hg. how much must the outside air be compressed to produce a cabin pressure in which the partial pressure of o2 is 0.200 atm?

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chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.

qualitative observation deals with data that can be observed with our senses: sight, smell, touch, taste, and hearing. they do not involve measurements or numbers. for instance, colors, shapes, and textures of objects are all qualitative observations.