unit 6: gases

variables for gas laws

P = Pressure

T = temp (in Kelvin)

V = Volume

n = Amount of gas in moles

boyle’s law

the pressure (P) and volume (V) of a gas are inversely related at constant temperature (T) and the amount of gas (n).

As one (volume or pressure) increases, the other decreases

independent variable

the aspect we are changing

dependent variable

a variable that changes in response to a change in the independent variable

controlled variables

the constant variables (the things that don’t change)

controlled variables in Boyle’s Law

temperature (T) and amount of gas (n)

independent variable in Boyle’s law

volume

dependent variable in Boyle’s law

pressure

example of Boyle’s law

in our lungs when we inhale the volume increases so pressure decreases and the opposite happens during exhalation, the volume of our lungs decrease so pressure increases

what do the different parts of PV = k mean

P = pressure

V = volume

k = constant

P1V1=P2V2

Boyle’s law equation

units of both Ps need to be the same and the units of both Vs need to be the same

charles’s law

Volume (V) and temperature (T) of a gas are directly related at constant pressure (P) and constant amount of gas (n)

as one increases, the other increases (ONLY APPLICABLE IF CONTAINER IS CLOSED AND FLEXIBLE LIKE A BALLOON)

independent variable in Charles’s law

temperature

dependent variable in Charles’s law

volume

controlled variables in Charles’s law

pressure (P) and amount of gas (n)

the pressure does change but because the container changes in size (volume changes), the pressure goes back to being the same thing

V1/T1 = V2/T2

equation of Charles’s Law

MUST convert temp to Kelvin (Tk = Tc + 273)

STP

Standard Temperature and Pressure

0 degrees Celsius OR 273 degrees Kelvin (TEMP)

AT

1 atm = 760 mmHg = 760 torr = 101.325 kPa (PRESSURE)

avogadro’s law

the volume of a gas is directly related to the number of moles (n) of gas at a constant temperature and pressure

as one increases, the other increase

ONLY APPLICABLE IS CONTAINER IS FLEXIBLE

controlled variables of Avogadro’s law

pressure (P) and temperature (T)

independent variable of Avogadro’s law

moles of gas (n)

dependent variable of Avogadro’s law

volume (V)

V1/N1=V2/N2

equation of Avogadro’s law

n MUST be in moles

Gay-Lussac’s Law

the pressure (P) and temperature (T) of a gas are directly related at a constant volume (V) and amount of gas (n)

so as one (pressure or temp) increases, the other increases

applicable when the container is rigid

controlled variables of Gay-Lussac’s Law

amount of gas (n) and volume (V)

independent variable of Gay-Lussac’s Law

temperature

dependent variable of Gay-Lussac’s Law

pressure

P1/T1=P2/T2

equation of Gay-Lussac’s Law

MUST convert temp to Kelvin (Tk = Tc + 273)

P1V1/T1n1=P2V2/T2n2

the combined gas law (with moles)

just cross out the variables that are constant and this can be used for any of the previous laws

when to use the combined gas law

use for all problems (EXCEPT ideal gas laws), just cross out variable not mentioned/don’t change