The major components of the Earth's atmosphere
78% nitrogen and 21% oxygen. Remaining are various gases - .9% argon 0.03% carbon dioxide
The main elements in the Earth's crust
49.2 % oxygen, 25.7% silicon, 7.4% aluminum
discovered oxygen in 1774 by heating mercuric oxide in an enclosed container with a magnifying glass.
What oxygen compounds can be decomposed easily to create oxygen in the lab
potassium chlorate - KClO₃. Manganese dioxide (MnO₂) is used as a catalyst to lower the temperature to decompose the KClO₃ and speed up the reaction.
Speeds up the rate of reaction by lowering activation energy needed for reaction. The catalyst is not changed.
Percent of oxygen in atmosphere and earth
In atmosphere 21%. In earth's crust 50%
Normally a gas; colorless, odorless, tasteless, and slightly heaver than air. Only slightly soluble in water, so you can collect the gas over water. At ⁻183C it changes to a pale blue liquid with magnetic properties. Oxygen does not burn but does support combustion. Most stable form is O₂
O₃ Occurs in small quantities in Earth's atmosphere. Has higher energy than oxygen so more reactive. Can form around high voltage electricity. 3O₂ + elec = 2O₃. Prevents harmful UV rays (skin cancer)
Found by Cavandish. Named by Lavoisier. Means "water former". Usually a gas, colorless, tasteless, odorless, tasteless when pure. Weighs 0.9 grams per liter; slightly soluble in water; becomes liquid at ⁻240C and a pressure of 13 atmospheres. It diffuses (moves from place to place in gases) more rapidly than other gas
Electrolysis Method of producing Hydrogen
Electrolysis of water (electric current passed through to decompose). Most common.
Displacing with metal to create Hydrogen
1. Cold water metals: Very active metal (potassium, calcium,sodium) + Cold Water = Hydrogen + metal hydroxide. Eg: with Sodium: 2Na + 2HOH -> H₂(g) + 2NaOH
2. Hot water metals: Magnesium + hot water
3. With metal and dilute acid (aluminum, zinc, iron, tin) Active metal + Dilute acid -> Hydrogen + Salt of the acid. Eg with Zinc, sulfuric acid, and hot water:
Zn + dil. H₂SO₄ -> H₂(g) + ZnSO₄
Industry production of Hydrogen
2. Passing steam over red hot iron
3. Decomposing natural gas (usually methane, CH₄) with heat (CH₄ + H₂O -> CO + 3H₂
Chemical properties of Hydrogen
1. Burns in air or in oxygen, giving off large amounts of heat. Its high heat of combustion makes a good fuel.
2. It does not support ordinary combustion.
3. Good reducing agent; withdraws oxygen from many hot metal oxides
Measurements of pressure
1 atm= 760mm Hg = 760 torr = 101,325 Pa = 101.3 kPA
1 All gas particles are in constant, random motion.
2 All collisions between gas particles are perfectly elastic (meaning that the kinetic energy of the system is conserved).
3 The volume of the gas molecules in a gas is negligible.
4 Gases have no intermolecular attractive or repulsive forces.
5. The average kinetic energy of the gas is directly proportional to its Kelvin temperature and is the same for all gases at a specified temperature.
Average kinetic energy
Temperature - when you read the temperature of something you are reading its average kinetic energy
The random movement of gases from one position to another. Rate of diffusion is the rate of the mixing of gases
The passage of gas through an orifice into a chamber. Rate of effusion - how fast gas moves through the orifice into the chamber
Graham's Law of Effusion/Diffusion
the rate of effusion of a gas is inversely proportional to the square root of its molar mass; this relationship is also true for the diffusion of gases
if a given quantity of gas is held at a constant pressure, its volume is directly proportional to the absolute temperature.
Solve for V₁ -> P₂V₂/P₁
Solve for P₁ -> P₂V₂/V₁
Solve for P₂ -> P₁V₁/V₂
Solve for V₂ -> P₁V₁/P₂
Gas pressure = atmospheric pressure - h (height of the mercury). When reading a barometer you read the top of the tube for mercury and the bottom for water
gas pressure = atmospheric pressure + h (height of mercury)
Combined Gas Law
Combination of Boyle and Charles
P₁V₁/T₁=P₂V₂/T₂ - be sure to convert torr to atm - divide torr number by 760
Gay-Lussac's Law - Pressure versus Temperature
If the temperature of a container is increased, the pressure increases.
If the temperature of a container is decreased, the pressure decreases.
Why? Suppose the temperature is increased. This means gas molecules will move faster and they will impact the container walls more often. This means the gas pressure inside the container will increase, since the container has rigid walls (volume stays constant).
Solve for P₂ = P₁ x T₂/T₁
Solve for P₁ = P₂ x T₁/T₂