CHEMISTRY COMMUNITY

vicenteruelos3

Does activation energy change with temperature?

vicenteruelos3

also, there is no transfer of matter between the system and the surroundings

vicenteruelos3

Catalysts are not consumed so in the steps of the reaction, the species that is used as a reactant in one step, and comes out as a product in a future step is the catalyst

vicenteruelos3

maybe it could be possible if the potential gibbs free energy of the reactants is equal to the potential gibbs free energy of the products. but it is probably super rare

vicenteruelos3

it at the beginning so we use the initial rate because any rate after could be affected by products going back to reactants

vicenteruelos3

false because the rate is dependent on the concentration of the reaction
r=k[A]^2
so if you change [A] then the rate also changes

vicenteruelos3

experimentally we usually only consider the forward reaction. the example in the book with the reaction with ozone and O2, they consider the reverse reaction because in the atmosphere there is no way to isolate the products so the products are able to turn back into reactants and affect the rate law

vicenteruelos3

all reactions have to overcome a specific activation energy this is what determines the rate of the reaction (kinetics)
whether or not the products are in a higher or lower energy state than the reactants determines if the reaction is favorable (thermodynamics)

vicenteruelos3

another example is the decomposition of nitrogen dioxide

2NO2(g)-->2NO(g)+O2(g)

r= k[NO2]^2

vicenteruelos3

yes since each step is a reaction and all the steps together form the overall reaction, the number of steps is equal to the number of intermediate reactions

vicenteruelos3

Will we be given the table with the reduction half reaction potentials?

vicenteruelos3

a vertical line represents an interface between phases in contact with each other
while a comma represents two different things not separated by anything

vicenteruelos3

if you use the equation Ecell= Ecathode - E anode then you dont have to switch the sign from the table

if you use the equation E cell= Ecathod + E anode then you do have to switch the sign from the table

vicenteruelos3

you use an inert conductor as the electrode when dealing with half reactions that have no conducting solids.
because I2(s) is not a conductor, you use platinum as the electrode

vicenteruelos3

The advantage to using Lavelle’s is that you can calculate k at different temperatures if delta h is known

vicenteruelos3

why is change in entropy surroundings equal to 0 for irreversible free expansion but not for reversible?

vicenteruelos3

why is the total change of entropy not always 0?

vicenteruelos3

one relation is that delta s of the system plus delta s of the surroundings is equal to delta s total

vicenteruelos3

q is equal to deltaU at constant volume becuase delta u = q plus w, so at constant volume there is no expansionary work (w=0)

vicenteruelos3

to isolate k you would do e^lnk

and for the other side of the equation e^....

vicenteruelos3

Why is a bomb calorimeter an isolated system?

vicenteruelos3

the q = n C deltaT is for molar heat capacity

vicenteruelos3

the heat absorbed by the calorimeter is equal to the heat released by the reaction

vicenteruelos3

it depends on the starting temperature of the ice and the final temperature of the water vapor if the starting temp of ice is less than 0 and the final temp of water vapor is over 100 degrees celcius then you would use MCdeltaT three times once to go from <0 to 0, phase change, then to go from 0 to ...

vicenteruelos3

What is the difference between qv and qp?

vicenteruelos3

One difference is that standard reaction enthalpy is in KJ, while standard enthalpy of formation is in KJ/mol

vicenteruelos3

On the heating curve, the sloped lines represent heat capacity

vicenteruelos3

a reaction mixture that consists of .400 mol H2 and 1.60 mol I2 was introduced into a 3.00 Liter flask and heated. at equilibrium, 60.0% of the hydrogen gas had reacted. what is the equilibrium constant K for the reaction.

why is the answer in 2 sig figs?

vicenteruelos3

one bond angle is also slightly less than 120 degrees

vicenteruelos3

yes it is the area where electrons are being shared. it is just the imaginary straight line that connects the nuclei of atoms bonded to each other in a molecule

vicenteruelos3

oh i think i meant to say NH

so why is dissociation energy of CH higher than that of NH

vicenteruelos3

why does CH have a higher dissociation energy than CN

vicenteruelos3

why is oxygen and nitrogen switched for ionization energy and not for electronegativity if electonegativity is based on ionization energy??

vicenteruelos3

you would use the wave function to describe an electron with wavelike properties and indeterminacy in momentum and position in an atom. it is also the radial wavefuntion times the angular wave function. this shows how orbitals change with angles and radii

vicenteruelos3

oxidation state is referring to the charge. a plus 4 charge is at a higher oxidation state than a plus 3 charge

vicenteruelos3

oxygen and nitrogen are exceptions to the trend for ionization energy, not for electronegativity. we expect oxygen to have higher IE than nitrogen but nitrogen has higher IE. this is because of the p orbital. oxygen has 4 electrons in the p subshell, while nitrogen has 3. because nitrogen has 3 elec...

vicenteruelos3

the formal charge of carbon in ch3 is 0.
valence electron=4
lone electrons=1
bonded electrons/2=3

4-(1+3)=0
FC=0

vicenteruelos3

because noble gases have very high ionization energy and very low electron affinity, they do not form chemical compounds easily. however when they are ionized or under pressure, they are able to make chemical compounds. so, yes they can make chemical compounds even tho they have a full outer shell

vicenteruelos3

you can use the equation

frequency= (.5 x mass of electron x velocity of electron squared +work function) /plancks constant

i got that from
Energy of photon - work function = kinetic energy of electron
energy of photon = h x frequency
and
KE = .5mv^2

vicenteruelos3

yes, the energy required to remove an electron is equal to the work function or threshold energy

vicenteruelos3

to find the concentration after the dilution you use (M initial)(volume initial) = (molarity final)(volume final)
(.2 x 1)/(4) = final molarity

that equals .05M
you use 4 because its final volume in the equation

vicenteruelos3

this isn't one of the homework problems, but question H.18 asks what the chemical equation is for the incomplete combustion of heptane gas. i was just wondering how to do it??

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