Gases

Question 1

gases have no fixed ___

Answer 1

volume

this, makes them more compressible then solids and liquids and their densities are very low.

Question 2

what are the most important properties of a gas?

Answer 2

pressure
volume
temp

Question 3

kinetic molecular theory describes the behaviours of gasses and is based on what assumptions ?

Answer 3

1) the molecules of gas are so small compared to spacing between them that the molecules themselves take up no volume
2) the molecules of gas are in constant motion . the collisions of the molecules with the walls of the container define the pressure of the gas and all collisions are elastic ( means that total kinetic energy is the same after the collision as it was before).
3) molecules of gas have no intermolecular forces
4) average kinetic energy of the molecules is directly proportional to the absolute temperature (temp is kelvins)

A GAS THAT SATISFIES ALL THESE REQUIREMENTS IS AN IDEAL GAS

Question 4

what is the SI unit for volume?

Answer 4

cubic meter (m^3)  but in chemistry cubic centimeter (cm^3) and L (litre) are commonly used. one cubic meter is equal to one thousand litres. 
1cm^3 = 1 ml 
1 m^3 = 1000 L

Question 5

Relationship between Celsius and Kelvin

Answer 5

T (in K) = T (in celcius) +273.15

Question 6

when dealing with gas, what’s the best unit for temp?

Answer 6

kelvin!

Question 7

What is pressure?

Answer 7

force per unit area
SI unit for pressure is pascal
1 pascal = N/m^2
1 atm = 760 torr =760 mmHg =101.3 kPa (KILOPASCALS)

Question 8

Standard temp and pressure

Answer 8

STP means temperature of zero degrees celcius (273.15K) and a pressure of 1 atm.

Question 9

The idea gas law equation is

Answer 9

PV=nRT
R: universal gas constant 0.0821 L-atm/K-mol
T: absolute temp of the gas (Kelvins)

Question 10

What happens when the pressure is constant?

Answer 10

amount of gas often remains the same so the n drops out
r = constant so it drops out
therefore we get V/T= k
therefore the volume is proportional to temperature
therefore, if the pressure is constant, volume and temp are proportional.
KNOWN AS CHARLES LAW

Question 11

What happens when the temperature is constant ?

Answer 11

PV=k therefore P and volume are inversely porportional
THIS IS BOYLE’S law
as the volume decreases the pressure will inc
and as the volume increases, pressure will decrease.

Question 12

what happens when the volume is constant?

Answer 12

P/T=k . pressure is proportional to the temp.

if the temp goes up, so does the pressure.

Question 13

what is the combined gas law?

Answer 13

PV/T

Question 14

what is the standard molar volume of an ideal gas at STP ?

Answer 14

Volume that 1 mole of a gas, any ideal gas would occupy at 0 degrees Celsius and 1 atm of pressure.
pv=nrt formula to calculate ! volume = 22.4 L

Question 15

Deviations from Ideal Gas Behaviour

Answer 15

under some conditions like high pressures and low temps the assumptions of ideal gas don’t hold up.
- particles in real gas have attractive intermolecular forces, therefore lead to fewer collisions on the wall of the container. this results in smaller than normal gas pressure.
therefore, P real gas < P of the ideal gas

Question 16

volume

Answer 16

for an ideal gas, volume of the individual particles of the gas is negligible. but at high pressures, the volume occupied by each gas particle becomes a greater proportion of the gas sample. so it is no longer negligible and it would reduce the free space available for particle movement.
therefore,
volume real gas < volume of ideal gas

Question 17

The vander waals equation

Answer 17

includes terms to account for the diff in the obv behaviour of real gases and calculated properties of ideal gases.
the an^2/ V^2 term serves as a correction for the intermolecular forces that generally result in lower pressures for real gases
nb: corrects for the physical volume that the particles occupy in a real gas.
a and b are both known as the van der waals Constants and are generally larger for gases that experience greater intermolecular forces and have larger molcular weights and therefore volumes.

Question 18

Summary

Answer 18

gases that behave the most ideally have the weakest intermolecular forces and the smallest volumes. by maintaining, conditions of high temperatures and low pressures, potential interactions between particles are minimized and particle volume remains insignificant compared to the container size.

Question 19

Daltons law of partial pressures

Answer 19

if there are 3 gases in a single container, the total pressure is due to collisions of all 3 types of molecules with the container walls.
daltons law states that the total pressure is simply the sum of the partial pressures of all the constituent gases.

Ptotal= Pa + Pb+ Pc
We also need to look at the mole fraction. the partial pressure of a gas is equal to its mole fraction times the total pressure. 
Pa= XaPtotal.
Pb= XbPtotal
Pc= XcPtotal.

Question 20

Grahams law of effusion

Answer 20

effusion is the escape of a gas molecule through a very tiny hole into an evacuated region
rate of effusion of gas a /rate of effusion of gas b = square root of (molar mass of gas b/molar mass of gas a)

grahams law states that the rate of effusion of a gas is inversely proportional to its molecular weight. so lighter gases effuse more quickly than heavier gases.

the molecules of 2 diff gases at same temp have the same kinetic energy but molecules of 2 diff gases at the same temp don’t have the same average speed. l