Thermodynamics Unit 4

kinetic theory of gases

explains the behavior of gases at a molecular level and assumes gas molecules are in constant and random movement

1. describe the pressure of ideal gas

   1. relationship between RMS and temperature

key takeaways of kinetic theory of gases

equal

Vavg along x,y, and z are what?

0

Vavg in 1 dimension equals what?

increase in sqrt(t)

when does RMS increase

decrease in sqrt(t)

when does RMS decrease

velocity distribution

describes the variation in particle velocity

symmetric peak

what is the general shape for velocity distribution

it gets wider

what happens to the peak in a greater velocity distribution

it gets narrower

what happens to the peak with a smaller velocity distribution

its wider at higher temps

how does temp affect the velocity distribution peak

the bigger the molar mass the more narrow

how does the change in mass affect the peak of velocity distribution

asymmetric

what is the general shape of the maxwell speed distribution

higher temperature the wider the peak

how does temp affect the peak of a maxwell speed distribution

slower speed, lower peak

how does speed affect the peak of a maxwell speed distribution

most probable speed, average speed, and root-mean-square

what are the 3 benchmark values of speed

Vmp > Vavg > Vrms

compare the benchmark values when looking at a graph

gas effusion

process that a gas escapes from a tiny opening into a vacuum

diffusion is from low to high and effusion is into a low area (vacuum) from a difference in pressure

compare diffusion and effusion

effective speed

depends on direction of molecule

mean pathway

average distance a gas particle travels

it decreases

what happens to the mean pathway with an increase of pressure

it increases

what happens to the mean pathway when the particle size increases

chemical kinetics

studies timescale of chemical reactions

extensive because of the number of moles, but can make intensive by dividing by volume

are reaction rates intensive or extensive

homogenous reation

single phase/molecule reaction

heterogenous reaction

2 or more phases in a reaction

rate law

a homogenous reaction that describes the relationship between reactant concentrations and rate of chemical reactant

reaction order

exponent with the concentration

overall reaction order

sum of reactant exponents

EXPERIMENTALLY

reaction orders must be done _________

rate constant (k)

proportionally between concentrations and rate of chemical reactant

concentrations

what are rate constants independent of

temperature and pressure

what are rate constants dependent of 

s-1

unit of 1st order k

m-1 s-1

unit of 2nd order k

m-2 s-1

unit of 3rd order k

linearly decreasing

what is the graph of 1st order when derived (ln[A]/ln[Ao]])

exponentially decreasing

what is the graph of 1st order when derived [A]/[Ao]

straight line

what is the graph of a 2nd order when derived

half life

time for half the reactant concentration to decrease

helps solve faster

why is half-life beneficial

1st order is independent of concentration while 2nd order is dependent

what is the difference conceptually between 1st order reaction and 2nd order type 1 reaction half-life

because the reactants might not be in a 1:1 proportion

why can you not do the half-life for 2nd order type 2

rate determining step

the smallest rate constant

steady-state approximation

when you set time derivatives to zero and is important because it is easier to solve

parallel reactions

when single reactants can become numerous products; where we can calculate the quantum yield

A

the frequency factor and has the same units as K

Ea

the activation energy ; J/mol

linear

slope: -Ea/R

y-intercept= ln(A) 

graphing the Arrhenius equation