The three main states of matter that we meet daily are: gas, liquid, and solid.
We will be looking at the first state of matter, gas. Gases can be compressed, they expand to fill their containers. The volume of a gas is variable
This is model for the behavior of an ideal gas. It is useful for predicting the behavior of gases. •Ideal gas particles are so small that they take up no volume compared to the total volume of the gas. •Ideal gas particles are in constant, rapid, random motion, moving in straight lines in all directions till they collide with other particles.
•There are no attractive or repulsive forces between particles and all collisions are elastic.
•The average kinetic energy of the particles is directly proportional to the absolute temperature. ( in kelvins)
In this room right now are millions of gas molecules and atoms colliding with the walls, the floor, your face and each other.
Can you feel it?
Our atmosphere is a mixture of gases that consist mainly of nitrogen, N2, and oxygen,O2.
Table 1: Average composition of the troposphere & lower stratosphere Constituent % by volume Natural formation Natural Depletion Nitrogen 78.08 Lightning, soil bacteria Oxygen 20.94 Argon 0.93 Carbon dioxide 0.035 Neon 0.0018 Helium 0.0005 Ozone 0.00006 UV reacting with O2 Hydrogen 0.00005 Methane 0.00017 Krypton trace Xenon trace
Earth’s Atmosphere provides the perfect conditions for life on this planet. There is plenty of oxygen for respiration, it protects us from solar radiation and it moderates the planets temperature.
One property of gases is that they exert pressure. The pressure exerted by the gas mixture we call air is called atmospheric pressure. The atmosphere that surrounds Earth is a sea of air. It exerts a force on the surface of the planet. Above you is a column of air that is exerting a force on you. This pressure can be measured.
Why is air pressure important? It causes wind Creates clouds and clear skies Allows us to predict the weather
Atmospheric pressure can be measured using a barometer, invented in 1643 by Evangelista Torricelli.
This barometer was filled with mercury, Hg.
He found that at sea level atmospheric pressure could support a column of mercury 760mm high.
This pressure comes from the mass of air pulled toward the center of the earth by gravity. Changing weather conditions cause this pressure to vary. The height of the column of Hg is not always 760 mm.
Units of Pressure:
mm Hg (millimeters of mercury) torr atm (standard atmosphere)
Pa (SI unit for pressure) pascal 1.000 atm = 760.00 mm Hg = 101,325 Pa Engineers measure pressure in psi (pounds per square inch)
1. The pressure of a tire is 28 psi, what is this in atm, torr, and pascals?
1.000 atm = 14.69 psi 28 psi x 1.000 atm /14.69 psi = 1.9 atm
1.000 atm = 760.0 torr
1.9 atm x 760.0 torr /1.000 atm = 1.4 x 10 3 torr 1.000 atm = 101,325 Pa 1.9 atm x 101,325 Pa / 1.000 atm = 1.9 x 10 5 Pa
Irish scientist Robert Boyle experimented with the relationship between pressure and volume of gases. He set-up a J-shaped tube and added mercury to see what it did to the volume of a trapped gas.
As pressure increased volume decreases.
This relationship is inversely proportional, when one increases the other decreases.
P = pressure V = volume k = a constant at a specific temperature
Pressure times a volume equals a constant.
P1 V1 = k
P2 V2 = k P1 V1 = k = P 2 V2 therefore P1 V1 = P2 V2
So if you know P1, V1 and V2 you can calculate P2 1 2 1 2
V P P V
If you have a gas at a pressure of 56 torr and a volume of 1.5L What will be the new volume (V2) if the pressure is increased to 150 torr?
P 1 V2 V1 P2
= 1.5L x 56 torr /150 torr
= 0.56L
In an automobile, the cylinder volume is 0.725L. After the piston moves up, the volume is 0.075L. The fuel-air mixture initially has a pressure of 1.00atm. Calculate the pressure (P2) of the compressed fuel-air mixture, assuming that the temperature remains constant.
Initial Conditions Final Conditions P1 = 1.00 atm P2 = ? V1 = 0.725L V2 = 0.075L
V1 0.725L P P 1atm 9.7atm 2 1 V2 0.075L
French physicist Jacques Charles was the first to fill a balloon with hydrogen gas and make a solo flight. He showed that the volume of a gas increases when the temperature increases (at a constant pressure)
Charles’s experimental results
As the temperature drops, the volume decreases. This is a linear relationship.
As you cool gases they eventually liquefy. If you extend (extrapolate) these straight lines you will find that they all to go a zero volume at -2730C. Zero degrees kelvin.
This temperature is called Absolute zero. The closest we have got to absolute zero is 0.00001 K
The direct proportional relationship between volume and temperature is represented by this equation.
V bT V b constant T
This law holds if the gas is held a t a constant pressure.
A 2.0L sample of air is collected at 298 K and then cooled to 278 K. (The pressure is held constant at 1.0 atm)
Does the volume increase or decrease? What is the volume of air at 278 K?
V constant T V1 V2 T1 T2
Initial Conditions Final Conditions T1 = 298 K T2 = 278 K V1 = 2.0L V2 = ?
V1 2.0L V 2 T2 278K 1.9L T1 298K
A sample of gas at 15 ° C (at 1atm) has a volume of 2.58L. The temperature is then raised to 38°C (at atm).
Does the volume of the gas increase of decrease? Calculate the new volume
Initial conditions T1 = 15C V1 = 2.58 L Final conditions T2 = 38C V2 = ?
You must convert the temperature from °C into K
T1 = 15°C = 15 +273 = 288K +273 = 311K T2 = 38°C = 38
T2 311K V2 V1 2.58L 2.79L T1 288K
Avogadro investigated the relationship between the volume of a gas and the number of moles present in the gas sample.
He found that as the number of moles is doubled (at constant temperature and pressure), the volume doubles.
Volume is directly proportional to the number of moles
V a constant n
Suppose you have a 12.2 L sample containing 0.50 mol of oxygen gas, O2, at a pressure of 1 atm and a temperature of 25°C. If all of this O2 is converted to ozone, O3, at the same temperature and pressure, what will be the volume of the ozone formed? 1. Write a balanced equation for the reaction 2. Calculate the moles of O3 produced
3O2(g) 2O3(g)
2molO3 0.50molO2 0.33molO3 3molO 2
Initial conditions n1 = 0.50 mol V1 = 12.2 L
Final conditions n2 = 0.33 mol V2 = ?
V1 V2 n1 n2 n2 0.33mol V2 V1 12.2L 8.1L n1 0.50mol
The volume decreases, because there are fewer molecules present in the gas after O2 is converted to O3.
The ideal gas law combines the three gas laws we have looked at so far. k (at constant T and PV k or V Boyle’s law; P n) Charles’s law; V bT Avogardro’s V an (at constant P and law: n) Where k,b,and a are constants. So we can combine this (at constant T and three gas laws to form the ideal gas law. P)
Tn VR P or PV nRT
PV nRT
R is the universal gas constant. When the pressure is expressed in atm and the volume in L, R always has the value of 0.08206 L atm / K mol
Temperature needs to be in Kelvin. A gas that obeys this equation is said to be behaving ideally.
A sample of hydrogen gas, H2, has a volume of 8.56L at a temperature of 0°C and a pressure of 1.5 atm. Calculate the number of moles of H2 present in this gas sample. P = 1.5 atm V = 8.56 L T = 0°C = 0 + 273 = 273K
PV = nRT
PV n RT (1.5atm)(8.56L) 0.57mol Latm (0.08206 )(273K) Kmol