CHEMISTRY COMMUNITY

Kyle Rex 1K

does activation energy depend on the number of moles of something or is it a constant value for a certain reaction?

Kyle Rex 1K

if a chemical equation is balanced and all the reactants and products have a stoichiometric coefficient of 1, for example, would the rates of formation for the products be the same as the rate of consumption of the reactants?

Kyle Rex 1K

they are proportional in that if you increase temperature, k will increase as well and also vice versa if you decrease temperature

Kyle Rex 1K

i think so because there are much more applications with the instantaneous rate law, such as differential rate law, integrated rate law, and for things like finding the half life of species and such

Kyle Rex 1K

because for a first order rxn, the plot for a linear slope would be: ln[A]= -kt + ln[A(initial)]

When comparing it to the linear form y=mx+b, you'll see that -k is m, or the slope. so to find k, you would multiply the slope, -k, by -1

Kyle Rex 1K

it is temperature dependent because the equation delta G = -RTln(k) and also k is dependent on temperature too . also Delta G naught is when pressure is constant so there's that

Kyle Rex 1K

I know the units of k is dependent on the order of the rate equation, but how do we use that knowledge to determine the units of k?

Kyle Rex 1K

to find the order of C you want to find the experiments where [C] changes, but [A] and [B] remain constant, which would be experiments 1 and 4. to do this, you set up a rate equation but with fractions, with the numerator being the experiment where [C] is largest (so it's easier). You would get: (70...

Kyle Rex 1K

increasing the concentration of a reactant will have a greater effect on second order rxns because the rate = k[A]^2 for second order vs rate = k[A] for first order

Kyle Rex 1K

so for first order reactions, its typically one of the molecules thats first order reacting with the solvent molecules, so technically it is only one of the atoms/molecules in question. Zero order essentially renders a molecule "useless" with the overall rate as the slow step determines th...

Kyle Rex 1K

for a, the answer says the cell diagram is Hg|Hg2 2+||NO3-, H+|O (g)| Pt

how did they get this as the cell diagram?

Kyle Rex 1K

when writing the cell diagram and the reduction reaction will require a Platinum electrode, does the diagram look like (for example) ||Cl-|Pt or is it ||Pt|Cl- or does it even matter

Kyle Rex 1K

since its starting with Au+, the oxidation reaction would be Au+-->Au3+ (bc losing e-) and the reduction would be Au+--->Au(s) (bc gaining e-). really for balancing you would just be adding electrons to each side, then multiply both half reactions by the coeffeicient that would give you an equal num...

Kyle Rex 1K

since O2 is in it's most stable form at standard conditions, its oxidation state would be 0 . Same applies for other elements in their standard state (ie. H2, Cl2, etc)

Kyle Rex 1K

since the work is work max, and work max is = to $\Delta G$ , which is = to nFE(cell), then work max= nFE(cell)

Kyle Rex 1K

did anyone else get a really large number? I got 2240kJ and I dont think this seems right

Kyle Rex 1K

When adding the OH- to balance the H+, do you have to add it to both sides?

Kyle Rex 1K

when balancing by using stoichiometric coefficients, you do that to balance things that are not either Oxygen or Hydrogen

Kyle Rex 1K

you can calculate the oxidation numbers of all of the different elements constituting the molecules and if an oxidation number increases, then that atom/molecule is oxidized, and if the oxidation number decreases then that atom/molecule is reduced

Kyle Rex 1K

when an oxidation number decreases, is it reduced? or is it oxidized because does the oxidation number lowering correlate to a loss of electrons?

Kyle Rex 1K

since its isothermal it means energy cannot come in or leave, so by nature the change in energy would be zero

Kyle Rex 1K

Cv is when there is no change in volume and Cp when there is no change in pressure

Kyle Rex 1K

is solving for reaction entropy like the same as solving for reaction enthalpy where its the sum of products molar entropy - sum of reactants molar entropy or is there another formula we have to use?

Kyle Rex 1K

It says containers B and C have 1 mole of atoms bound into diatomic molecules. Does this mean that it's 1 mole of diatomics or .5 mol of diatomics bc the 1 mol of atoms would be split in half? and how would the entropies compare of 1 mol of atoms vs diatomics?

Kyle Rex 1K

How is entropy related to pressure? And does this change depending on what type of system is being dealt with?

Kyle Rex 1K

Not really yet since we haven't gotten to the gibbs free energy equation deltaG=deltaH - T(deltaS), in which a reaction is spontaneous if its delta G is negative.

Kyle Rex 1K

For the reaction 4KClO3 (s) ---> 3KClO4 (s) + KCl (s), what sign should the standard reaction enthalpy be? I got a negative number, but since it's 1 solid going into 2 wouldn't it make sense that the entropy would be increasing?

Kyle Rex 1K

How would you rank these in terms of relative entropy levels?

Kyle Rex 1K

I'm pretty sure the reversible part is just so we understand that the q value we're using is at its maximum, and also I don't think Lavelle said anything about having to worry about irreversible reactions

Kyle Rex 1K

When given amount of moles and a final and initial volume, what equation and how do we use it to find change in entropy?

Kyle Rex 1K

the kJ/mol numbers in question are probably coming from a table that's giving you each molecules deltaH of formation, which is why it's being multiplied by the number of moles of the specific molecule. O2 and N2 aren't included because they're pure molecules, and the delta H of them is 0. Everything...

Kyle Rex 1K

The equation for the conversion is given to us, but when using anything with delta T, the difference in temp will be the same if you use K or C, so it doesn't really matter

Kyle Rex 1K

if work is a piston compressing the gas and the work is given as 300kJ (for example), when solving for delta U of the gas inside a close container using delta U=q+w, would w be positive or negative?

Kyle Rex 1K

When calculating internal energy changes, is that the deltaU equation or q?

Kyle Rex 1K

it could be solid, liquid, aqueous, or gas, it just depends what it happens to be at standard conditions: 1 atm and 25C

Kyle Rex 1K

noooo only aqueous and gases are put in the ice table

Kyle Rex 1K

since there is a higher concentration of reactants, the excess of reactants will react to form product, which is why it favors the products since it goes in that direction

Kyle Rex 1K

by thinking about what each molecule is, you could get a general idea, but it would probably be smart to do the ICE tables just incase the pHs are very close to one another

Kyle Rex 1K

Ka x Kb = Kw, so like a higher Ka for an acid (meaning it is a strong acid) would result in a lower Kb for its conjugate base (meaning it's really weak, which makes sense bc its a strong acid)

Kyle Rex 1K

After finding the concentration of H3O+ from the pH, do we have to subtract this amount from the initial concentration of HClO2?

Kyle Rex 1K

they are logarithmically proportional. so if kb is big (strong base) then pkb will be small. If kb is small (weak base), then pkb will be larger. same goes for ka and pka

Kyle Rex 1K

I don't think Lavelle is expecting us to use the equation because we've pretty much moved on to acids and bases and he hasn't told us about it. I'm pretty sure the way he would want us to do it is to use PV=nRT to convert the concentration to partial pressure (or vice versa) and solve for k after

Kyle Rex 1K

like the person above said you'd have to use a graphing calculator or a program online like desmos and to do so just move all parts to one side of the equation so it equals zero, put that into the graphing program and find where the graph crosses the x axis to get the value for "x"

Kyle Rex 1K

for part b what is the importance of "x" being a halogen? also how would you go about solving part b

Kyle Rex 1K

since water has [H3O+] of 10^-7, if the acid gives a concentration of less than that, for example {H3O+] of 3x10^-9, if you add that to the [H3O+] from the autoprotolysis of water, the change in concentration of H3O+ will not have been significant enough to make a difference in the pH, then the pH w...

Kyle Rex 1K

I'm sure there is a threshold that K can reach, but it wouldn't be because of speed or anything. It'd simply have to do with the relative concentrations or pressures of the products and reactants

Kyle Rex 1K

Since the K is not given for the whole equation, you have to add up two of the equations from the table to get the equation from the problem. After doing that, you take the two K values from the equations you added together and multiply the Ks to get the new K value for the overall equation.

Kyle Rex 1K

It depends one whether the reaction is endothermic or exothermic, and you would just treat "heat" as a reactant or product (depending on which side it's on), and use Le'Chatlier's principle to determine which side an increase or decrease in temperature would cause the reaction to proceed to.

Kyle Rex 1K

yes! you include aqueous solutions in both K and Q. Water is a pure liquid, so I don't know why it'd be labeled as aq, but if it's water gas then yea use it

Kyle Rex 1K

Honestly, its really situational when you'd have to omit something, so if you're ever confused you could just solve for x with it being in the top and bottom, and in the end the solution (omitting the 2x^2 or not) would pretty much be the same.

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