CHEMISTRY COMMUNITY

Jack Hewitt 2H

k' is the reverse reaction constant and can be used in the equation K = k/k'

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Ea forward > Ea Reverse: Endothermic
Ea forward < Ea Reverse: Exothermic

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The intermediate is the molecule formed in step 1 that is then used in step 2.

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Yes, because total rate order is found by adding the exponents of the reactants.

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A negative order signifies that the concentration of the reactant inversely affects the reaction rate.

Jack Hewitt 2H

As long as the conversion is correct it should not matter. However, the best practice may be to give your answer in the units that were stated in the question.

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Unique Rate: Rate divided by stoichiometric coefficient
Instantaneous: The slope of the tangent line at a specific moment

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By looking at the number of molecules participating in the rate determining step of the reaction you can determine molecularity.

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The one would be implied just as it would be in a math class.

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It's best to understand how you would get to the half life to help with the conceptual aspects of this section.

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Because when the first order half-life equation is derived the initial concentration terms will cancel out.

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Temperature is the only thing that can change the value of K.

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Endothermic Reaction: Increase in temperature will cause the reaction to shift to the right.
Exothermic Reaction: Increase in temperature will cause the reaction to shift to the left.

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Open systems: Exchange both matter and energy with the surroundings
Closed systems: Exchange just energy
Isolated systems: Neither heat nor matter can be exchanged

Jack Hewitt 2H

Yes, when volume does not change work or "w" is equal to 0.

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The problem should give you enough information to determine which to use.

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Ecell is calculated by subtracting the reduction potential of the oxidized half reaction (Anode) from the reduction potential of the reduced half reaction (Cathode).

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You should use 5/2R if pressure is constant and 3/2R if volume is constant.

Jack Hewitt 2H

Try not to round to sig figs until the end of the problem to ensure accurate answers.

Jack Hewitt 2H

Yes, the bonds broken release energy (reactants) and the bonds formed require energy (products).

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q=nC(delta)T when given # of moles
q=mCdeltaT when given mass
q=C(delta)T when moles = 1

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Because the steam has more heat and therefore a higher enthalpy.

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Because the substance can withstand more heat the slope will be much less steep.

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Yes, the reaction would be in equilibrium if it was reversible.

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Delta G > 0 ; Not spontaneous
Delta G < 0 ; Spontaneous
Delta G = 0 ; Equilibrium

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Oxidation state is the number of electrons an element needs to gain or lose to reach a neutral state and can be found by using the periodic table.

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The more negative the value of Ecell is the stronger the reducing agent is.

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You would use OH- when balancing the hydrogens in a basic solution.

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For an acidic solution you would use H20 and H+ to balance the hydrogens and oxygens while in a basic solution you would use H20 and OH- to balance the hydrogens and oxygens.

Jack Hewitt 2H

Both steps are needed to balance the reaction.

Jack Hewitt 2H

K = 0 ; delta G = 0
K < 1 ; delta G > 0
K > 1 ; delta G < 0

Jack Hewitt 2H

I will not be able to make the review session tonight. Can someone post the answers given?

Jack Hewitt 2H

Soyoung Park 1H wrote:Do we have to memorize numbers such as c=3.00x10^8 m/s and planck's constant (h=6.63x10^-34Js) for the test?

No you do not we are given a constants and equations sheet. However it may be helpful to memorize them to some extent so you can do problems faster.

Jack Hewitt 2H

danielruiz1G wrote:in the de Broglie equation why does it state that any moving "particle" , when the examples talk about cars. can any moving object talk have a wavelength?

Yes any moving object has wavelength, but with large objects such as cars the wavelength is irrelevant.

Jack Hewitt 2H

Chase Yonamine 1K wrote:In the equation, E=hv, does E represent the energy of the photon or does it represent the energy required to remove an electron?

e represents the energy of a photon. The works function represents the energy required to remove an electron.

Jack Hewitt 2H

Madeline Lequang 1G wrote:Does the formula (1/2)mv^2 only apply to kinetic energy? or can it be used for other types of energy?

It only applies to kinetic energy.

Jack Hewitt 2H

When doing calculations, should we use 2.99792 × 10 8 m.s -1 or 3.00 × 10 8 m.s -1 for the speed of light? I used the 3.00 × 10 8 m.s -1 on the midterm and got an answer that was two hundredths off and got it marked wrong, so what should be the accurate number to use? Look at the sig figs in the pr...

Jack Hewitt 2H

Sarah Bui 4I wrote:Hi! I was just wondering which element has a higher electron affinity nitrogen or carbon and why? I think this is one of the exceptions and I am not sure.

Carbon has a greater affinity for electrons than nitrogen because of its half filled p subshell which makes it more stable than Nitrogen.

Jack Hewitt 2H

Madelyn Cearlock wrote:For the question that asks why do we balance chemical equations, what was the exact answer that was desired? Thank you!

Because of the law of conservation of mass.

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chrisavalos- 1K wrote:What is the rule for a combustion equation? Do they always produce Carbon Dioxide and Water? I have just never been sure of this. Thank You.

Yes, combustion reactions will always produce CO2 and H2O.

Jack Hewitt 2H

Do we round the answer in every step of the calculation, or do we just round the final answer to the number of significant figures? Because when I round the answer in every step, my final answers are often different from those given by the textbook. It is best to only round your answers at the very...

Jack Hewitt 2H

Lily Smith 4C wrote:Where do you find the mass of an atom on the periodic table?

It is listed under the element in their box on the periodic table.

Jack Hewitt 2H

Number of valence electrons - (number of lone electrons + number of lines drawn)

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chrisdinkel_1K wrote:do we have to determine relative Electronegativites by periodic trends or is it given?

You have to use periodic trends to determine relative electronegativities.

Jack Hewitt 2H

So I know that Br, I, and P can break the octet rule in lewis structures, but I read that there are other elements that can do this too, like Cl occasionally. Which elements are we required to know that break the octet rule for this class? It is better to think of it conceptually that if an element...

Jack Hewitt 2H

How can you tell which molecules have a greater bond length without having its Lewis structure? I know when you have two ions you look for polarizability but what about when you have multiple elements involved? You would need to draw the Lewis structure to determine which molecules have a greater b...

Jack Hewitt 2H

melissa_dis4F wrote:For the electron configuration of Pd I get [Kr]4d^8 5s^2 but it is [Kr] 4d^10. My question is do we change it to [Kr] 4d^10 because we should fill in the entire d orbital before continuing to the 5s orbital? Is this always?

Yes this is always. It is one of the exceptions to the octet rule.

Jack Hewitt 2H

Melissa Villanueva 3D wrote:How would we solve for the work function? Like what type of information would be given to use in order to find the work function and how would we use the given. Thanks!

You rearrange the formula as you would with an algebraic equation and plug in what is given to solve for the work function.

Jack Hewitt 2H

chrisavalos- 1K wrote:I was wondering what the trend for electronegativity was, is it the same as ionization energy?

Yes, the trend for electronegativity is the same as the trend for ionization energy.

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jane_ni_3b wrote:How should we know which ones are exceptions?

The most common exceptions we deal with are found in the 3rd period because of an unfilled d-orbital.

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Arlene Linares 3A wrote:How do we figure out the AXE formula? I am still having trouble with this.

A is the central atom. X is the number of atoms bonded to the central atom. E is the number of lone pairs on the central atom.

Jack Hewitt 2H

danielruiz1G wrote:is it possible to determine the shape of a molecule if you're only given the AXE formula, if so how do you do it?

Yes because the AXE formula tells you the regions of electron density which is all you need to determine the shape.

Jack Hewitt 2H

KarlaArevalo4D wrote:Does anyone have an easy way to find the hybridization of the central atom they are able to share? Much appreciated.

The easiest way is to consider the number of regions with electron density. This includes lone pairs.

Jack Hewitt 2H

Arshia Ramesh 1G wrote:i read on one of the reviews that a pi bond is weaker than a sigma bond but why is that?

It is because a pi bond does not allow for rotation and would break while a sigma bond does allow for rotation.

Jack Hewitt 2H

Phoebe Chen 4I wrote:Are the bond angles in square planar less than or equal to 90?

They are equal to 90.

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kevinav wrote:What would be the molecular shape for the general formula AX3E

The molecule would have a trigonal pyramidal molecular shape.

Jack Hewitt 2H

Moryel Yashar 1J wrote:Are lone pairs taken into consideration when determining the hybridization of a central atom?

Yes lone pairs are taken into consideration because they are still areas of electron density.

Jack Hewitt 2H

How do I determine which compound is a Lewis Acid and which compound is a Lewis base?

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Nicholas Le 3A wrote:Is the central atom in the Lewis structures based off of which atom has the lowest electronegativity or which atom has the lowest ionization energy?

It is based off of lowest ionization energy.

Jack Hewitt 2H

904837647 wrote:So the midterm should be formatted just like the test?

Yes, the midterm should be formatted similarly to the tests.

Jack Hewitt 2H

Do we know how many questions from each section will be in the test? Like how many from the fundamentals, quantum, and chemical bonds? I know there’s 8 but how is it going to be divided? My TA said that the amount of questions from each section would correlate to the amount of time we spent on said...

Jack Hewitt 2H

You do not need to fully memorize the spectrum but it will definitely be helpful to be familiar with it for the course.

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The car was too large to have "measurable wavelike properties".

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The test required students to know correct units as well as significant figures.

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Does anyone actually know when the discussion posts are due?

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Does anyone know if we need to write the different states of matter in each equation?

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Dr. Lavelle hasn't said how many questions the test will be nor how it will be graded.

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