CHEM Exam 3

law of conservation of energy

energy cannot be created or destroyed, but it can be transferred

energy

the capacity to do work or produce heat

potential energy

energy that results from an object’s position

kinetic energy

energy associated with motion

system

the part of the universe chosen for a study (in a chemical reaction, usually reactants and products)

surroundings

everything outside of the system

open system

exchanges matter and energy with its surroundings (ex. hot soup in an open bowl)

closed system

exchanges energy, but not matter, with it surroundings (ex. hot soup in a sealed container)

isolated system

exchanges neither matter nor energy with its surroundings (ex. hot soup in an insulated thermos)

internal energy

sum of all kinetic and potential energy within the system

energy can be transferred between the system and surroundings

energy can be transferred as..

heat (q) and work (w)

heat (q)

transfer of thermal energy between the system and surroundings due to a temperature difference

SI unit of heat

joule (J)

heat capacity (C)

quantity of heat required to change the temperature of a system by 1°C or 1K; an extensive property that depends on the amount of substance and what substance it is

temperature change depends on

amount of heat transferred (q) and heat capacity of the system (C)

if a substance has a large heat capacity…

it will be more resistant to temp change VV

specific heat capacity (C_s)

heat required to raise the temperature of 1g of a substance by 1°C (J/g°C)

molar heat capacity (C_m)

heat required to raise the temperature of 1 mol of a substance by 1°C

work (w)

energy transferred when a force acts over a distance

pressure-volume (PV) work

for gases, expansion or compression can transfer energy between the system and surrounding as work

if volume compresses…

work is done on the system (+w)

if volume expands…

work is done by the system (-w)

fewer moles of gas produced is…

compression, work done on the system (+w)

more moles of gas produced is…

expansion, work done by the system (-w)

first law of thermodynamics

energy cannot be created or destroyed, but can be transferred or converted from one form to another

heat entering the system

(+q)

heat exiting the system

(-q)

state function

depends on current state of the system, independent of the path taken to reach that state (ex. internal energy, pressure, volume temperature)

path function

depends on how the system moves between states, differebt paths can give different values (ex. heat and work)

enthalpy (H)

a state function that accounts for the internal energy of a system and the energy associated with its pressure and volume

at constant pressure…

ΔH=q

endothermic

heat enters the system, system absorbs heat, surroundings cool down, +ΔH

exothermic

heat exits the system, systems releases heat, surroundings warm up -ΔH

ΔH_f°

enthalpy change when 1 mol of substance (product) is formed from its constituent elements

ΔH_f°=0

for elements in standard states

gases standard states

H₂(g), N₂(g), Cl₂(g), F₂(g), and noble gases

liquids standard states

Hg(l), Br₂(l)

solids standard states

C(graphite), S₈(s), P₄(s), I₂(s), metals

Hess’s law

when going from a particular set of reactants to a particular set of products, the enthalpy change is the same whether the reaction occurs in one step or a series of steps

heat (q)

transfer of thermal energy between the system and surroundings due to a temperature difference, heat flows from higher temperature to lower temperatyre

thermal equilibrium

both objects have the same temp

heat of reaction (q_rxn)

heat absorbed or released by a chemical reaction under specified conditions

calorimetry

the experimental measurement of heat transferred during a physical or chemical process, uses temperature changes to determine amount of heat transferred

calorimeter

device used to measure heat transfer

coffee-cup calorimeter

simple, insulated container that operates at a constant pressure

coffee-cup calorimeter

a simple, insulated container that operates at a constant pressure; consists of two styrofoam cups, reaction mixture, thermometer, stirrer

when reactions at a constant pressure..

ΔH=q

electromagnetic radiation (EM radiation)

energy that travels through space as electromagnetic waves (ex, radio waves, microwaves, x-rays, visible light)

waves

disturbances that transfer energy through space

wavelength (λ)

distance between two consecutive peaks (or troughs)

amplitude (A)

height or depth of a crest or trough

frequency (ν)

number of waves that cycles that pass a point each second (in Hz or s^-1)

wave speed

distance traveled by a wave per minute (m/s)

electromagnetic spectrum

full range of electromagnetic radiation, organized by wavelength and frequency

as wavelength increases..

energy decreases and frequency decreases

as wavelength decreases..

energy increases and frequency increases

order of energy of the electromagnetic spectrum from shortest wavelength to greatest wavelength

gamma rays, x-rays, ultraviolet, visible light, infrared, microwaves, radio waves

interference

when two or more waves overlap and combine; constructive and destructive

constructive interference

waves interact in phase, increases amplitude/light intensity

destructive interference

waves interact out of phase, decreases amplitude/light intensity

diffraction

bending and spreading of waves as they pass through an opening or around an obstacle; go through constructive and deconstructive interference and create dark spots and bright spots

blackbody radiation

electromagnetic radiation emitted by an object due to its temperature, as object gets hotter it emits more radiation and changes color (ex. stovetop)

intensity reaches a maximum…

then decreases at shorter wavelengths

E=hc/λ

energy is directly proportional to wavelength, frequency and energy are inversely proportional to wavelength

wave behavior

interference and diffraction

particle behavior

photoelectric effect

photoelectric effect

electrons are ejected from a metal surface when light of sufficiently high frequency strikes it

incident frequency < threshold frequency (v₀)

no electrons are ejected, regardless of intensity

incident frequency > threshold frequency (v₀)

electrons are ejected

when incident frequency