chem 30 cumulative
What is Earth's atmosphere?
A layer of gases surrounding Earth, held by gravity, protecting life by absorbing UV radiation, retaining heat, and moderating temperature extremes.
How much mass does the atmosphere have, and where is most of it?
The atmosphere has a mass of 5 quintillion kilograms, with 75% within 11 km of the surface.
Where does the atmosphere end?
It has no definitive boundary, but 100 km altitude (the Kármán Line) is commonly used as a reference.
What is "air"?
The part of the atmosphere used for breathing and photosynthesis, found near Earth's surface.
What are the primary components of Earth's atmosphere?
Nitrogen (78%), Oxygen (21%), Argon (0.9%).
What are trace gases?
Gases that make up 0.1% of the atmosphere, including carbon dioxide, methane, water vapor, nitrous oxide, and ozone.
What natural and industrial substances may also be present in air?
Natural substances include dust, pollen, volcanic ash, and sea spray. Industrial pollutants include chlorine compounds, fluorine compounds, mercury, and sulfur compounds.
What are the five layers of the atmosphere?
Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere.
What defines the troposphere?
The lowest layer, containing 80% of atmospheric mass and 99% of its water vapor.
What is the altitude range of the troposphere?
From Earth's surface to 7 km at the poles and 20 km at the equator.
How do temperature and pressure change in the troposphere?
* Temperature decreases from 15°C at ground level to -75°C at the top.
* Air pressure decreases from 101.3 kPa to about 10 kPa.
What weather events occur in the troposphere?
Nearly all weather phenomena, including clouds and storms.
What is the stratosphere known for?
It contains the ozone layer, which absorbs UV radiation.
What is the temperature range in the stratosphere?
Rises from -50°C at the bottom to 0°C at the top due to solar radiation absorption.
How effective is the ozone layer?
The ozone layer, about 1 cm thick, absorbs 97-99% of UV radiation.
What happens in the mesosphere?
* Temperatures drop to as low as -100°C, making it the coldest atmospheric layer.
* Meteors burn up here due to collisions with gas particles.
What characterizes the thermosphere?
* Temperatures can reach up to 1500°C.
* Low air density prevents significant heat transfer to objects.
What natural phenomenon occurs in the thermosphere?
The aurora borealis, caused by ionization of gas particles.
What defines the exosphere?
The outermost layer, extending from the thermosphere to about 190,000 km, halfway to the Moon.
What is the exosphere made of?
Mostly hydrogen and helium, with particles spaced so far apart they rarely collide.
How was Earth's early atmosphere formed? What role did photosynthesis play?
From volcanic gases, primarily carbon dioxide, water vapor, ammonia, and methane. Photosynthetic bacteria began producing oxygen, increasing its levels while reducing carbon dioxide.
How does the early atmosphere compare to today’s?
* Early: 95% CO2, 4% O2, high temperatures (~400°C).
* Today: 78% N2, 21% O2, moderate temperatures (~20°C).
What happened to ammonia in the atmosphere?
It broke down into nitrogen and hydrogen, with hydrogen escaping into space.
What is absolute zero?
The temperature at which particle motion ceases (-273°C or 0 K).
What instrument measures atmospheric pressure?
A barometer, invented by Evangelista Torricelli in 1643.
What is atmospheric pressure at sea level?
101.3 kPa or 760 mmHg.
What does Boyle’s Law state, how do you graph it?
At constant temperature, pressure and volume are inversely proportional: P1V1=P2V2. the plot results in a downwards curve.
What does Charles’ Law state, how do you graph it?
At constant pressure, volume and temperature are directly proportional: V1/T1=V2/T2. the plot results in a straight line..
What does Gay-Lussac’s Law state, how do you graph it?
At constant volume, pressure and temperature are directly proportional: P1/T1=P2/T2. the plot results in multiple straight lines, where every line represents the relationship between pressure and temperature for a different gas.
What is the Combined Gas Law?
Combines all three laws: the relationship among pressure, volume, and temperature of a fixed amount of gas. P1V1/T1=P2V2/T2
What does Dalton’s Law state?
The total pressure of a gas mixture equals the sum of partial pressures in a gas mixture. the components act independently of each other: Ptotal=P1+P2+P3…
How does a barometer work?
Mercury adjusts in a tube to balance atmospheric pressure, with normal atmospheric pressure at 760 mmHg. the weight of mercury creates a vacuum in the top of the tube.
What is a manometer used for?
Measuring gas pressure in closed systems by comparing mercury levels in a U-shaped tube. has a known pressure (possibly vacuum) on one side and the unknown pressure on the other. calculated based on the difference in height between the two sides.
matter definition
* Anything that has mass and occupies space. Mass is the amount of matter in an object.
physical states of matter
* Solid: Has a definite shape and volume, with tightly packed particles that vibrate in place and strong intermolecular forces (IMFs).
* Liquid: Has a definite volume but no definite shape, particles move freely, are moderately attracted to each other, and take the shape of the container.
* Gas: Has no definite shape or volume, particles are far apart with weak or no attraction, and is highly compressible.
* Plasma: ionized gas
types of solids
1. Crystalline Solids
* Particles have a regular repeating pattern (e.g., ionic compounds like salt).
2. Amorphous Solids
* Particles are arranged randomly (e.g., plastic, glass).
liquids- properties and behavior
* Slightly compressible, particles have translational motion, and liquids can flow.
gases- properties and behavior
* Highly compressible, particles move by diffusion (high to low concentration) and effusion (high to low pressure through an opening). Gases, like liquids, are fluids, meaning they can flow.
definition of pressure
* Result of gas particles colliding with container walls; calculated as force per unit area.
measuring atmospheric pressure
Measured with a barometer; mercury is used due to its high density, which allows a measurable column at sea level (760 mmHg or 1 atm)
pure substance
* Has a fixed composition and properties, cannot be separated by physical processes.
* Element: Pure substance with one type of atom.
* Compound: Two or more elements chemically combined, with unique properties.
mixture
* Variable composition and properties, can be separated by physical processes.
physical properties
* Characteristics that don’t change the substance’s composition (e.g., density, color, melting point).
chemical properties
* Characteristics describing how a substance reacts with other substances, changing composition (e.g., flammability, reactivity).
physical change
* Change that doesn’t alter the substance's composition and is often reversible (e.g., melting, dissolving).
chemical change
* Change that forms new substances and alters composition; generally not reversible (e.g., burning, rusting).
definition of heat
* Thermal energy transferred due to a temperature difference between two bodies.
temperature
* Measures average kinetic energy of particles in a substance (K.E. = ½ mv²).
heat transfer
* Flows from high to low temperature and can occur by:
* Conduction: Heat transfer through direct contact.
* Convection: Heat transfer by motion of fluids.
* Radiation: Heat transfer without a medium (e.g., sunlight).
KMT of gases key info
* Gases consist of tiny, fast-moving particles with little attraction.
* The distance between particles is large, so the actual volume of particles is minimal.
* Particles move in straight lines, with elastic collisions causing pressure.
* Average kinetic energy of particles is directly proportional to temperature.
kinetic energy distrubution curve
* Shows the number of particles at various speeds in a sample at a certain temperature; higher temperatures increase the average speed and kinetic energy of particles.
change of state
* Occurs when matter absorbs or releases energy without changing temperature (e.g., melting, boiling).
energy absorbtion and release
* Absorbing energy: Solid → Liquid (melting), Liquid → Gas (evaporation).
* Releasing energy: Gas → Liquid (condensation), Liquid → Solid (freezing).
temperature plateaus
* During phase changes, energy overcomes IMFs rather than raising temperature, resulting in a constant temperature until the phase change completes.
definition of vapor pressure
* Pressure of a vapor in equilibrium with its liquid or solid in a closed container.
* Higher temperature increases vapor pressure, allowing more particles to escape into the vapor phase.
influence of imfs on vapor pressure
* Stronger IMFs in a liquid lower vapor pressure as fewer molecules can escape.
boiling vs evaporation
1. Boiling Point
* Temperature at which vapor pressure of a liquid equals atmospheric/ barometric pressure, allowing bubbles to form and rise within the liquid.
2. Evaporation
* Surface-only process of liquid turning into gas at temperatures below boiling point.
phase diagrams purpose
* Graphical representation of a substance's phases under varying temperatures and pressures.
phase diagrams key points
* Triple Point: Where all three phases coexist in equilibrium.
* Critical Point: Beyond which a substance becomes a supercritical fluid, with no distinction between liquid and gas.
phase diagram boundaries
* Fusion (Melting) Curve: Transition between solid and liquid.
* Vaporization Curve: Transition between liquid and gas.
* Sublimation Curve: Transition between solid and gas.
moving on a phase diagram
* Moving vertically (upward) increases density, while moving horizontally (rightward) increases kinetic energy.
definition of vapor
the gaseous state of a substance that is solid or liquid at room temperature
What is an atom?
The smallest unit of an element that retains its chemical properties, made of protons, neutrons, and electrons.
What defines the identity of an atom?
The number of protons in the nucleus, also known as the atomic number.
What is the atomic number (Z)?
The number of protons in the nucleus of an atom, which identifies the element.
What is the mass number (A)?
The total number of protons and neutrons in an atom's nucleus.
What is an isotope?
Atoms of the same element that have the same number of protons but different numbers of neutrons.
How do isotopes differ in mass?
Isotopes with more neutrons have a greater mass.
Why do isotopes have the same chemical properties?
Chemical properties depend only on the number of electrons, which isotopes have in common.
How are isotopes named?
By adding the mass number to the element’s name, e.g., potassium-39.
How do you calculate the number of neutrons in an isotope?
Number of neutrons = A - Z (mass number - atomic number)
What is the nucleus of an atom?
The central part of an atom, containing protons and neutrons, and accounting for most of the atom's mass.
What are protons?
Positively charged subatomic particles located in the nucleus.
What are neutrons?
Subatomic particles with no charge, located in the nucleus, that add to the atom's mass.
What are electrons?
Negatively charged subatomic particles orbiting the nucleus, with negligible mass compared to protons and neutrons.
What is the mass of an electron relative to a proton?
Electrons are about 1/5000 the mass of a proton, or approximately negligible.
What is the atomic mass unit (amu)?
A unit of mass equal to 1/12 the mass of a carbon-12 atom, approximately 1.6611x10^-24 grams.
Why was carbon-12 chosen as the standard for atomic mass?
Carbon-12 is a common element and ensures atomic masses are represented as whole numbers for most elements.
What is the atomic mass of an element?
The weighted average mass of an element's isotopes, as shown on the periodic table, measured in atomic mass units (amu).
How is the atomic mass on the periodic table calculated?
It’s a weighted average of all naturally occurring isotopes of the element.
What is Avogadro's constant?
6.02x10^23. he number of representative particles in one mole of a substance.
What is a mole (mol)?
The metric unit for measuring the amount of substance, defined as the number of atoms in exactly 12 grams of carbon-12.
What is molar mass?
The mass in grams of one mole of a substance, numerically equal to its atomic or formula mass in g/mol.
What are the representative particles for different substances?
* Element: Atoms
* Ion: Ions
* Ionic compound: Formula units
* Molecular compound: Molecules
What is formula mass?
The sum of the average atomic masses of all atoms in the formula of an ionic compound.
What is molecular mass?
The sum of the average atomic masses of all atoms in the formula of a molecular compound.
How do you convert moles to mass and vice versa?
* Moles to mass: moles x molar mass = g
* Mass to moles: g / molar mass = moles
How do you convert between mass and particles?
* Mass → Moles → Particles
* Particles → Moles → Mass
What is percent composition?
The percentage by mass of each element in a compound, calculated as (mass of element / mass of compound) x 100
Why is percent composition always constant for a compound?
The ratio of elements in a compound does not change, regardless of sample size.
How do you determine boiling point on a phase diagram?
Draw a line from 1 atmosphere to the liquid-gas boundary, then drop to the corresponding temperature.
What happens to a liquid in a closed container?
Evaporation and condensation occur at equal rates, maintaining equilibrium.
What happens to the mass of a gas in a closed container when the volume decreases due to pressure?
The mass remains constant.