# ch14 Flashcards

describe the motion of gas molecules

gas molecules move with constant brownian motion which is random motion of molecules caused by collisions with larger particles

how do gases exert a force (pressure) on it a container

the molecules continuously collide with each other and the walls of the container.

The collisions cause a change in momentum (impulse) which produces a force equal to the rate of change of momentum

this force gives pressure (P = F/A)

how do you get impulse from a force-time graph

impulse is equal to the area under a force-time graph

describe the pathing of particles

particles take a random path

they don’t travel in a straight line, but are constantly changing direction due to collisions, which is why diffusion is slow

equation for average distance moved (displacement)

distance moved = √N * step length (mean free step)

N = number of steps moved

step length = length of one step

boyle’s law

when gas is at a constant temperature, pressure P and volume V are inversely proportional

pV = constant

why does boyle’s law still work

as volume decreases, particles are closer together, increasing density and colliding more frequently

this exerts a greater force and therefore greater pressure on the container

1 bar = normal atmospheric pressure

the pressure in a car tyre is 2.6 bar

the tyre volume is 6 litres and the temp is constant

calculate the volume of gas that escapes if the tyre is punctured, assuming the tyre keeps its shape

pV = constant

first calculate constant

2.6 * 6 = 15.6 bar Litre

air will escape until the tyre pressure matches atmospheric pressure, 1 bar so work out volume after it’s expanded to that pressure

pV = 15.6 bar litre

V = 15.6 / P = 15.6 / 1

volume = 15.6 litres

but 6 litres remains constant in deflated tyre

volume escaping = 15.6 litre - 6 litre = 9.6 litre

how to calculate number of particles

number or particles = number of moles * Avogadro constant Na

how is pressure affected when the volume of a gas increases

when the volume of a gas increases, the space between molecules increases and so the time between collisions is larger

this cause the rate of collisions and so rate of change of momentum to decrease

this means the force exerted is lower, causing a decrease in pressure

what does Charles’ Law

at a constant pressure, volume V is directly proportional to absolute temperature T

number of moles =

number of moles =

mass of sample / mass of 1 mole

explain charles’ law

as temp increases, the average kinetic energy of the molecules increases

pressure is constant so the force and rate of change of momentum is constant

to keep it like this, the volume increases so the faster speed of molecules is compensated by the larger gaps between them

state pressure law

when a gas has a fixed volume, pressure is directly proportional to the absolute temperature

explain pressure law

as temperature increases, the average kinetic energy increases so speed of molecules increases

this increases the rate of collisions so producing a larger rate of change of momentum

this leads to a greater force exerted and so an increase in pressure