15. Gases

solids, liquids, gases - they all matter

gas

a state of matter with no fixed shape or volume, that diffuses to fill the container it is placed in

what can the volume of a sample of gas depend on?

temperature and pressure

temperature

a measure of the degree of hotness of an object

to convert from celsius to kelvin

+273.15

to convert from kelvin to celsius

-273.15

pressure of a gas

the pressure of a gas is the force that the gas exerts on a unit area of its container

what is pressure measured in?

Nm^-2 / Pascals (Pa)

to convert from kPa to Pa

x1000

to convert from Pa to kPa

divide by 1000

volume of a gas

the volume of a sample of a gas is the same as the volume of the container in which the sample is held

to convert from m^3 to cm^3

x10^6

to convert from cm^3 to m^3

divide by 10^6

at what temperature and pressure do we measure volumes of gas to compare them?

standard temperature and pressure (stp)

boyle's law

boyle's law states that at constant temperature and pressure, the volume of a fixed mass of gas is inversely proportional to its pressure

if volume increases, what does pressure do?

pressure decreases

if volume decreases, what does pressure do?

pressure increases

charles' law

charles' law states that at constant pressure, the volume of a fixed mass of gas is directly proportional to the temperature measured in Kelvin

if temperature increases, what does volume do?

volume increases

if temperature decreases, what does volume do?

volume decreases

combined gas law

P1V1/T1 = P2V2/T2

when using the combined gas law, what unit must all temperatures be in?

Kelvin

when using the combined gas law, the units for pressure and volume on either side must be…

consistent

gay-lussac's law of combining volumes

gay-lussac's law of combining volumes states that for reactions between gases at the same temperature and pressure, there is a simple whole number ratio of volumes of reactants and products

avogadro's law

avogadro's law states that equal volumes of gases contain equal numbers of particles under the same conditions of temperature and pressure

kinetic theory of gases assumption 1

gases are made up of particles that are in continuous rapid, random motion, colliding with each other and with the walls of the container

kinetic theory of gases assumption 2

there are no attractive or repulsive forces between the molecules of a gas

kinetic theory of gases assumption 3

the volume of gas particles are negligible

kinetic theory of gases assumption 4

the average kinetic energy of the molecules in a sample of gas is proportional to the temperature measured on the kelvin scale

kinetic theory assumption 2 limitation

gas molecules do have intermolecular forces between their molecules

kinetic theory assumption 3 limitation

it is not valid to say that the volume of the molecules of a gas is always negligible compared with the space that they occupy

ideal gas

one that perfectly obeys all assumptions of the kinetic theory of gases under all conditions of temperature and pressure

under what conditions do real gases come very close to ideal gas behaviour?

low pressure, high temperature

how do real gases differ from ideal gases?

forces of attraction and repulsion do exist between the molecules and the volume of the molecules is not negligible

ideal gas equation

PV = nRT

explain why Charles' law is consistent with PV = nRT

for a fixed mass of gas n is constant, R is constant, and P is constant according to Charles' law. therefore V is proportional to T

when using the ideal gas formula, P must be in…

Pascals

when using the ideal gas formula, V must be in…

m^3

when using the ideal gas formula, n must be in…

moles

when using the ideal gas formula, R is…

given on the front of the paper

when using the ideal gas formula, T must be in…

Kelvin

to work out RMM using moles and grams

divide grams by moles