A sample of oxygen is collected in a 175 mL container over water at 15°C, and the barometer reads 752.0 torr. What volume would the dry gas occupy at 770.0 torr and 15°C? (Water vapor pressure at 15°C is 12.8 torr.)

The volume of dry gas = 168 L

Given

175 ml container at 15°C

P total = 752 torr

water vapour = 12.8 torr

Required

The volume of dry gas

Solution

Dalton's law of partial pressure :

P tot = P₁ + P₂ + P₃  

P total = P O2 + P water

P O2 = 752 - 12.8

P O2 = 739.2 torr

Boyle's Law  

At a fixed temperature, the gas volume is inversely proportional to the pressure applied  

P₁V₁ = P₂V₂

739.2 175 = 770 .V₂

V₂ = 168 L

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.