Chemistry - Midterm #1 (Thermochemistry & Quantum)

Thermochemistry

The area of science concerned with the amount of heat absorbed or released during chemical and physical changes

energy

the capacity to supply heat or do work

work (w)

the process of causing matter to move against an opposing force. also defined as energy transfer due to changes in external, macroscopic variables such as pressure and volume

potential energy (and how chemical bonds affect it)

the energy an object has because of its relative position, composition, or condition. weak bonds been higher potential energy, more reactivity; strong bonds means lower potential energy and greater stability

kinetic energy

the energy an object possesses because of its motion, associated with the random motion of atoms and molecules

law of conservation of energy (first law of thermodynamics)

energy can neither be created nor destroyed, although it can be changed in form. also states the internal energy of a system changes through heat flow into our of the system, or work done on or by the systemin

internal energy (U or E)

the total of all possible kinds of energy present in a substance; is a state function

state function

a property whose value depends only on the state that a system is in, and not on how that state is reached. enthalpy and internal energy are state functions. heat and work are notsy

system

the substance or substances undergoing the chemical or physical change being studiedsur

surroundings

all other matter, including components of the measurement apparatus, that serve to either provide heat to the system or absorb heat from the system

exothermic process

a chemical reaction or physical change that releases heat. system releases heat to surroundings (q<0)

endothermic process

a chemical reaction or physical change that absorbs heat. the system gains heat from the surroundings (q>0)

thermal energy

kinetic energy associated with the random motion of atoms and molecules

temperature

a quantitative measure of “hotness” or “coldness,” directly related to the average kinetic energy of the atoms and molecules in an object; an intensive property

heat (q)

the transfer of thermal energy between two bodies at different temperatures

joule (J)

the SI unit of heat, work, and energy. defined as the amount of energy used when a force of 1 newton moves an object 1 meter (1 J = 1 N*m = 1 kg*m²/s²)

calorie (cal)

a unit of heat or other energy; the amount of energy required to raise 1 gram of water by 1 degree Celsuis. defined as 4.184 J

nutritional calorie (Calorie or kcal)

commonly used in quantifying food energy content, is a kilocalorie (1 Calorie = 1000 cal or 1kcal)

Heat capacity

quantity of heat a body of matter absorbs or releases when it experiences a temperature change of 1 degree celsius/kelvin; an extensive propertyh

specific heat capacity

the quantity of heat required to raise the temperature of 1 gram of a substance by 1 degree celsius/kelvin; an intensive property

calorimetry

the technique used to measure the amount of heat involved in a chemical or physical process

calorimeter

a device used to measure the amount of heat involved in a chemical or physical process

coffee cup calorimeter

a simple calorimeter used to measure the energy change for reactions in a solution at constant pressure. assumptions include neglecting heat absorbed by calorimeter and assuming solution’s specific heat and density are similar to waters

bomb calorimeter

a device designed to measure the energy change for processes occuring under conditions of constant volume, commonly used for reactions involving solid and gaseous reactants or products, such as combustion

enthalpy change

the heat released or abosrbed by a system under constant pressure during a chemical or physical process. negative indicates exothermic. positive indicates endothermic.

thermochemical equation

a chemical eequation that represents changes in both matter and energy, showing the enthalpy change value associated with the reaction for the given number of moles of reactants and productss

standard state

a commonly accepted set of conditions used as a reference point for reporting thermodynamic properties (1 bar pressure, 1 M conc for solutions, pure liquid/solid for substances, most stable form for elements 25 C), designated by superscript o

standard enthalpy of combustion

the enthalpy change when 1 mole of a substance burns under standard state conditions

standard enthalpy of formation

the enthalpy change for a reaction in which 1 mole of a pure substance is formed from its free elements in their most stable states under standard state conditionsh

hess’s law

if a process can be written as the sum of several stepwise processes, the enthalpy change of the total process equals the sum of the enthalpy changes of the various steps; valid because enthalpy is a state function

wave

an oscillation or periodic movement that can transport energy from one point in space to another

electromagnetic rediation

energy transmitted by waves that have an electric-field component and a magnetic field component. these waves can travel through a vacuum at a constant speed

speed of light

a fundamental constant representing the speed at which electromagnetic radiation travels through a vacuum, approx 2.998 × 10^8 m/s

wavelength

the distance between two consecutive peaks or troughs in a wave

frequency

the number of wave cycles that pass a specified point in space in a specified amount of time, measured in hertz (Hz or 1/s)

amplitude

the magnitude of a wave’s displacement, related to the intensity (brightness for light, loudness for sound)

electromagnetic spectrum

the entire range of all types of electromagnetic radiation, including radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays

interference pattern

a pattern, typically consisting of alternating bright and dark fringes, that results form constructive and destructive interference when two or more waves come into contact or pass through narrow slits

standing waves (stationary waves)

localized wave phenomena constrained within a region of space, characterized by discrete wavelength of integer numbers of half wavelengths (inherently quantized)

nodes

points, lines, or surfaces within a standing wave where the amplitude is zero and there is no motion

quantization

the limitation of some property to specific discrete values, rather than a continious range of values

blackbody

a perfect absorber of all electromagnetic radiation, when heated up, emits its own electromagnetic radiation thats spectrum depends only on its temperature

photoelectric effect

the phenomenon where electrons or ejected from the surface of a metal when light with a frequency greater than a certain threshold is shone upon it

photon

the smallest possible packet or quantum of electromagnetic radiation; a particle of light

wave-particle duality

the fundamental concept that elementary particles, such as photons and electrons, can exhibit both wave-like and particle-like properties

line spectra (discrete spectra)

electromagnetic radiation emitted at specific, discrete wavelengths by excited atoms or molecules, in contrast to a continious spectrum

bohr model of hydrogen atom

an early atomic model proposing that an electron moves around the nucleus only in specific circular orbits, each with a fixed radius and quantized energy

ground electronic state (ground state)

the most stable state of an atom, ion, or molecule, where its electrons occupy the lowest possible energy orbitals

excited electronic state (excited state)

a state where an atom, ion, or molecule has absorbed energy, causing an electron to move to a higher energy orbital

de Broglie Wavelength

the wavelength associated with a moving particle

Heisenberg uncertainty principle

a fundamental rule stating that it is impossible to simultaneously dtermine with perfect accuracy both the momentum and the position of a particle

wavefunction

a mathematical description of an atomic orbital that describes its shape and can be used to calculate the probability of finding an electron at any given location. the square of its magnitude represents the electron density

atomic orbital

a general region in an atom within which an electron is most probable to reside, described by a wavefunction

principal quantum number (n)

defines the electron shell, indicating the general energy level and average distance of an electron from the nucleus

angular momentum quantum number (l)

defines the subshell and shape of the orbital

magnetic quantum number (ml)

defines the spatial orientation of an orbital within a subshell (values from -l to l)

spin quantum number (ms)

describes the intrinsic quantum “spinning” of electron, with two possible values, ½ or - ½

radial node

a spherical surface where the probability of finding an electron for a given orbital is zero. number of radial nodes is given by n - l - 1

shell

A set of atomic orbitals that share the same principal quantum number

subshell

a set of atomic orbitals within a shell that share the same principal quantum number and angular momentum quantum number

degenerate orbitals

orbitals that have the same energy level. in multi electron atoms, this typicall refers to orbitals within the same subshell

pauli exclusion principle

states that no two electrons in the same atom can have the exact same set of all four quantum numbers; consequently, an atomic orbital can hold a maximum of two electrons, which must have opposite spins

aufbau principle

procedure for determining the ground state electron configuration of an atom byy building up the electron structure, addint electrons one by one to the lowest energy available orbitals

hunds rule

states that for degenerate orbitals, the lowest energy configuration for an atom is achieved by maximizing the number of unpaired electrons with parallel spins before pairing any electrons

valence electrons

the electrons located in the outermost principal quantum shell (highest n value) of an atom, which are primarily involved in chemical bonding and determine an atom’s chemical properties

core electrons

electrons in an atom that occupy the inner, filled shells, and are not typically involved in chemical bonding

shielding

the effect where inner electrons partially block the nuclear attraction from reaching the outer, valence electrons, reducing the effective nuclear charge experienced by the valence electrons

effective nuclear charge (Zeff)

the net positive charge experienced by an electron in a multi-electron atom, calculated as the nuclear charge (Z) minus the shielding effect of other electrons

covalent radius

one half the distance between the nuclei of two identical atoms when they are joined by a covalent bond

ionic radius

the measure used to describe the size of an ion, cations are smaller than their parent atoms, while anions are larger

isoelectronic

describes atoms/ions that possess the same electron configuration

Ionization energy (IE)

the minimum amount of energy required to remove the most loosely bound electron from a gaseous atom or ion in its ground state. successive ionization energies (IE1, IE2, etc) always increase

electron affinity

the energy change that occurs when an electron is added to a gaseous atom to form an anion, can be exothermic (negative value) or endothermic (positive value)