Gases

Pressure The pressure of a gas is the force it exerts on a unit surface area Pressure is measured with a barometer Measured using mercury in a sealed Normal is 760mm or 29.92 in high

Pressure Units The unit for pressure is pascal (Pa) which is a force of 1 Newton exerted on an area of one square meter (N/m3) 1 atm = 101,325 Pa or 101 kPa Torr are another system created by Evangelista Torricelli who invented the first barometer in 1643

Boyle’s Law P1V1 = P2V2 At a given temperature the volume occupied by a gas is inversely proportional to its pressure p= k (1/V) p pressure of gas V volume of gas k is a constant needed to make both sides equal

Boyle’s Law So at a given temperature, the product of the pressure and volume of gas must be constant! If pressure is increased, the volume must decrease P x V = k

Temperature Measured with a thermometer 3 scales: Celsius, Fahrenheit, and KELVIN Pg. 64

Charles’s Law The volume of a gas increases by 1/273 for each Celsius degree its temperature is increased -273.15 is lowest possible attainable temperature or absolute zero

Charles’s Law If we know the volume of a gas at one Kelvin, we can find its volume at any other temperature by the equation. The equation can also be used to find Kelvin given a known volume

Combined Gas Law Boyle’s law and Charles’s law are combined to make the following equation

Combined Gas Law The temperature and pressure at which the volume of a gas is measured are known as the conditions of measurement.

Combined Gas Law Let’s think about the relationship

Example Combined Gas Law A gas sample occupies 250mL at 27*C and 780 Torr pressure. Find its volume at 0*C and 760 Torr pressure

Example Combined Gas Law A gas sample occupies 250mL at 27*C and 780 Torr pressure. Find its volume at 0*C and 760 Torr pressure Convert the temperatures to the Kelvin scale by adding 273*C to each T1= 27*C + 273 = 300K T2 = 0*C + 273 = 273K

Example Combined Gas Law A gas sample occupies 250mL at 27*C and 780 Torr pressure. Find its volume at 0*C and 760 Torr pressure Equation: V2 = V1 x (P1/P2) x (T2/T1)

Example Combined Gas Law A gas sample occupies 250mL at 27*C and 780 Torr pressure. Find its volume at 0*C and 760 Torr pressure V2 = 250mL x (780 Torr/760 Torr) X (273K/300K) V2 = 234 mL

Each gas would have a volume of 1ft3 Standard Conditions All gases fill their containers completely! If we have a mixture of oxygen, nitrogen, and carbon dioxide gases and put the sample into a 1ft3 container, how much by volume of each gas will be present? Each gas would have a volume of 1ft3

Know These!!!! Standard Conditions Temperature Pressure 0*C 760Torr 32*F 29.92 in. 273K 1.000atm or 101kPa Know These!!!!