Test #2 Flashcards
What is thermochemistry?
The study of energy associated with chemical reactions
What is energy?
The ability to transfer heat (q) or do work (w)
What is heat (q)?
The ability to change temperature. Flows spontaneously from high to low.
What is work (w)?
Energy used to cause an object to move against a force.
What is kinetic energy?
The motion/speed of particles - relates to temperature. (KE=1/2mv2)
What is potential energy and how is electrostatic potential energy calculated?
The attraction or repulsion of charges.
(Eel=KQ1Q2/d)
Q1/Q2 = mass of charges
d = distance between charges
What are some conversion factors?
1 kJ = 1000 J
1 cal = 4.184 J
1 kcal = 1,000 cal = 1 Cal (dietary calorie)
What is the difference between the system and the surroundings?
System - the thing being studied (the reaction)
Surroundings - everything else outside the reaction
What is an open system?
A system that transfers heat and matter
What is a closed system?
A system that transfers heat but not matter
What is an isolated system?
A system that does not transfer heat or matter
What is the first law of thermodynamics?
Energy is conserved
What is internal energy?
The sum of all the kinetic/potential changes in a system.
Change in energy = heat + work
What is an exothermic reaction?
Heat was lost by the system (-q)
What is an endothermic reaction?
Heat was absorbed by the system (+q)
What does it mean to have -w?
Work was done BY the system ON the surroundings
What does it mean to have +w?
Work was done ON the system BY the surroundings
What is enthalpy?
The heat of a reaction at constant pressure when the only work done is pressure-volume work.
What is a thermochemical equation?
A chemical equation that also includes the change in heat information at the end
What is calorimetry?
A lab method for measuring the heat exchange involved in physical or chemical processes
What is heat capacity (c)?
The amount of heat needed by a certain substance to change its temperature by 1 degree celsius.
What is specific heat (cs)?
The amount of heat needed to change 1g of a substance by 1 degree celsius.
What is molar heat capacity (cm)?
The amount of heat needed to change 1 mol of a substance by 1 degree celsius
What happens if a substance has a large heat capacity?
It is hard to change its temperature. Ex. insulators (water, foam, etc.)
What happens if a substance has a small heat capacity?
It is easy to change its temperature. Ex. conductors (metals)
What is the calorimetry equation?
Allows us to calculate heat transfer.
q=mc(change in)T
q = heat
m = mass of substance changing temp.
c = specific heat
(change in) T = change in temp.
What are the steps of Hess’ Law?
- Get things on the right side of the reactions
- Look to make sure coefficients are correct
- Start canceling out
- Combine/cancel
What is electromagnetic radiation?
Energy transmission in the form of a wave traveling at the speed of light.
Red/Orange/Yellow - Low energy - 750 nm
Green/Blue/Violet - High energy - 400 nm
What is the conversion factor to convert nanometers to meters?
1 meter = 1 x10^9 nanometers
What is Avogadro’s number and what does it tell us?
6.02 x 10^23
It tells us how many particles (either atoms or molecules) are in 1 mol of a substance.
1 mol = 6.02 x 10^23
What is the atomic emission spectra?
Bohr observed that when elements were heated or electrified, they emitted unique colors of light
Why are the spectra unique?
Every atom has a specific number of protons and thus the energy levels are at different distances from the nucleus. Every atom has a unique radius.
What does the Bohr model demonstrate?
- Describes the atom as a small, positively charged nucleus surrounded by electrons that travel in specific circular orbits
- When an electron moves from a lower to higher energy level, it absorbs energy
- When an electron moves from a higher to lower energy level, it emits a photon of light
What are some limitations of the Bohr model?
- It only works mathematically for hydrogen
- Doesn’t explain bonding
- Electrons don’t actually move in set circular orbits
- The fact that electrons exist in different energy levels, transition between them, and emit light still apply
What is Heisenburg’s uncertainty principle?
It is impossible to know both the momentum and location of an electron at the same time.
What did DeBroghe discover?
Electrons have wave-like properties
What is the Aufbau Principle?
Electrons fill from the lowest energy orbital to the higher energy orbitals
What is the Pauli exclusion principle?
Electrons must have opposite spins in order to reduce repulsions and occupy the same orbital
What is Hund’s rule?
Electrons spread out within a sublevel before pairing up
What is periodic law?
When organized by atomic #, there is a periodic repetition of properties after a series of 1-8 valence electrons
What is effective nuclear charge (Zeff)?
The charge or “pull” felt by the outermost valence electron from the protons in the nucleus.
Zeff = # protons (atomic #) - shielding e- (nonvalence e-)
What is atomic radius?
The distance from the nucleus to the outermost valence electrons
What is ionic radius?
The distance from the nucleus to the outermost valence electrons after an atom has gained or lost electrons
What are the radius trends?
- Down a group, atomic radius increases.
- Across a period, atomic radius decreases
- Across a period, Zeff increases and principle energy level stays the same and gets pulled in closer by the increasing nuclear charge
What happens to the ionic radius when at atoms loses an electron?
It gets smaller
What happens to the ionic radius when at atoms gains an electron?
It gets bigger
