CHEMISTRY COMMUNITY

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I remember him saying that they're colliding against other molecules in the solution.

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If you look at how half life is derived from the original 1st order reaction equation the initial concentration is canceled out when deriving the half life, which is why it doesn't matter.

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If you look at each equation and plug in the units for each variable, solving for K will give you different units for zero, first, and second order.
The units are different because the equations are different.

For zero order, K = m/L x S
For first order, K = 1/sec
For second order, K= L/ mol x sec

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For something to be thermodynamically stable, it has to be spontaneous right? Even though it will not react

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Given a rate law and some proposed mechanisms, How do you determine which one is the slow step?

Is it the one that matches the given rate law, but what if none of them do?

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Consider the cell Ag(s)uAg1(aq, 5.0 mmol?L21)uuAg1(aq, 0.15 mol?L21)uAg(s). Can this cell do work? If so, what is the maximum work that it can perform (per mole of Ag)?

Hello using this equation for 6N17 gives you max work as a positive value. Based off the equation shouldn't it be negative?

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Even though your reaction may be flipped, you use the E naught value given because E naught is your reaction potential. It's not like Delta H naught where you can use Hesse's Law to change the signs or multiply. If you manipulate the equation the E naught stays the same.

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I noticed that some cell diagrams in the homework don't include salt bridges.. when is this possible?

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I noticed that some cell diagrams in the homework don't include salt bridges.. when is this possible?

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6N15. Calculate the potential of a cell constructed with two nickel electrodes. The electrolyte in one compartment is 1.0 m Ni(NO3)2(aq). In the other compartment, NaOH has been added to a Ni(NO3)2 solution until the pH 5 11.0 at 298 K. See Table 6I.1. I calculated this by assuming it's a concentrat...

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It's a mistake and you get the right answer if you use one.

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We're asked to predict the cell potential for 6N3. I'm having trouble with (a) Pt(s)|H2(g, 1.0 bar)|HCl(aq, 0.075 mol?L21) ||HCl(aq, 1.0 mol?L21)| H2(g, 1.0 bar)|Pt(s) I know you use the equation E=-RT/nF(logQ) because it is a concentration cell. I'm having trouble figuring out why n=1 how do you ca...

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If the oxidation number is increasing, it's being oxidized.
If the oxidation number is decreasing, it's being reduced.

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^^^
also, if you start balancing it with H+/OH- and H2O, a charge will pop up and you can tell based off that.

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I believe you write Cl2 --> 2Cl- in the products because this is the only way to go about doing the reduction. If you leave it as Cl2 --> Cl2 nothing is really happening in the reaction and rewriting it is equivalent but now you have a charge to work with.

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In acidic solutions you add H+ and in basic you add OH-

you basically add H20 in order to balance out the O
and H+/OH- to balance out the H

It can get more complicated so I recommend reading Toolbox 6k.1 and looking at examples in the book.

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In the equation you use to compare two temperatures you don't ignore deltaS/R it's just canceled out when subtracting the equations lnK(2)-lnk(1), lnk= (-delta H naught/RT) - (delta S naught/R).

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Delta G equals the maximum amount of work done at constant pressure and temperature.

I'm not sure if this is what you were asking but I hope it helps.

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Delta G equals zero when a reaction is at equilibrium, or when Q=K or K=1.

Van Hoff's equation is derived from delta G= delta H-Tdelta S. It is not used when G = zero, it is used to calculate K at different temperatures.

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That's correct. You know Mn has to be +7 in MnO4- because O4 has an overall -8 charge and the molecule has a -1 charge.

It is then being reduced to Mn 2+, as it's oxidation number decreases.

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When writing redox reaction equations,
If it is an oxidation reaction do you always write the number of electrons in the products? and for a reduction in the reactants?

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When writing half reactons why is the number of electrons written in the equation being added?

For example in this oxidation:
5Fe = Fe3+ + 5e-

Why is the 5e- added and not subtracted?

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How can you identify when you need to break the reaction down into 3 steps of heating, vaporization, then cooling?

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Degeneracy, W: X^n

X: #of possible states
n: #number of particles

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Yes, deltaU= q+W = 0 for an insolated system in an isolated universe demonstrates this.
Energy is neither created or destroyed, q= -w

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Cv is heat capacity at constant volume and Cp is heat capacity at constant pressure.
For atoms that are ideal gases:
Cv: 3/2 R
Cp: 5/2 R

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In a forward reaction, you do products over reactants for the equilibrium equation. For the reverse it is technically reactants over products, so it makes sense that your K would be 1/K for the reverse.

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I'm a bit confused about standard enthalpy of formation. So the definition is enthalpy for the formation of one mole of a substance from its elements in their most stable form and the standard enthalpy of formation of an element in its most stable form is zero. If it is always zero, why are we asked...

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Can you use bond enthalpy of the products minus reactants in Method 2?
Or does that only work in Method 3 with Standard Enthalpy of Formation?

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What conditions indicate that a reaction is at constant pressure?
How would you know if it involves changes in the number of moles of gas (P delta V is sigfnificant)??

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What is positional entropy and what equation should I use to calculate it?

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Building on this,
Can someone further explain the Boltzmann equation?

If we were calculating 5 particles in one of two states would W be 2^5 ??

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Does anyone know if all the thermochemistry and thermodynamic equations will be supplied on the midterm?

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For the notes on method 2, Lavelle said to remember that you need to add enthalpy of phase changes for liquids and solids.
Can someone explain this futher? Would you add it to the final HRXN?

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Yes, I believe you would assume it is a cylinder shape.

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Use the R that will cancel your units so you are left with J.
When doing the equation make sure to write out the units so you can see if they cancel.

It also helps to remember that J is the same as 1kg.m^2.s^-2

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If you have two equations that can be added together to get the wanted composite equation, you can add the deltaHRXN of each equation to get the net deltahHRXN.

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You used method three to calculate the standard enthalpy of formation if bond enthalpies are not available. The equation is (standard enthalpy of formation of the products) - (standard enthalpy formation of the product) = overall standard reaction enthalpy Make sure the reaction is balanced and mult...

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Is [h30+][0h-]= 1.0 x 10^-14 always true? what conditions does the reaction need to be under for this to be true ?

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A sample of CH3NH3Cl of mass 15.5 g is dissolved in water to make 450. mL of solution. What is the pH of the solution? I keep doing this and getting a PH of 2.6, the answers say it's supposed to be 5.42. I found the Ka to be 2.3 X 10^-5 = x^2/0.265-x I get x to be .0025 can someone tell me what i'm ...

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I also got a negative number.

Can ph be negative?

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Inert gases are noble gases that don't undergo chemical reactions. Noble gases often don't react with other substances because they're stable.

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Calculate the pH, pOH, and percentage protonation of sol- ute in each of the following aqueous solutions: (a) 0.057 m NH3(aq); (b) 0.162 m NH2OH(aq); (c) 0.35 m (CH3)3N(aq); (d) 0.0073 m codeine, given that the pKa of its conjugate acid is 8.21. Can someone please give a step by step for part (a)? I...

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When you manipulate an equation you also manipulate the K value, which is why you multiply the K values of the two equations to get your composite equation's K value.

For example if you multiply an equation by 2 you square the K value.

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If Q is less than K this tells you that products still need to form, so the reaction will go forward.
If Q is greater than K it tells you that there are more products and the reaction must go back towards the reactants.

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I know that when K is less than 10^-3 it favors the reacts,

but how strict is this cut off? if K is a little more than 10^-3 is it close enough to 10^-3 that it still favors the reactants? or does it favor neither products or reactants?

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A net ionic equation should only include what participates in forming the product, which is why you leave out spectator ions (ions that merely "spectate" without contributing). Spectator ions appear on opposite sides of a chemical equation and therefore cancel out.

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The partial pressure of 02 is different because the second experiment contains 0.5 mol 03 while the first one contains 0.1mol 03. Although the amount of Liters is the same, the different initial molar amounts of 03 change the overall partial pressure. This will affect the partial pressure of 02.

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If you look at a tetrahedral shape as an example, It is nonpolar if all the 4 surrounding molecules are the same element because the dipoles cancel out. The structure is symmetrical. but, If you have a tetrahedral shape in which the surrounding molecules are different elements, it will be polar. The...

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Carbon cannot exceed the octet rule. It is not large enough, not past the third row, and based on its valence number it likes to form 4 bonds.

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a coordination compound consists of a transition metal and ligands that are attached to it.

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is cisplatin a chelate?

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Ligands are neutral molecules/anions that bond to a central atom, forming a coordination complex.

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Do transition metal cations always form complexes w H20?

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The coordination number is just the number of bonds attached to the central atom and within the coordination sphere.

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Can someone explain the "cage" around the porphyrin ligand? and how it relates to its function?

Thank you!

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When naming a coordination compound
I know you name the ligand first but then is it the anion or transition metal?

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A Bronsted Acid is a proton donor, a Lewis Acid accepts an electron pair. These are interchangeable because they are saying the same thing. When a proton is donated, the molecule becomes more negative, which is like accepting an electron pair. Bronsted and Lewis acids are the same thing, just a diff...

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I don't think you can ever have two central atoms.
When there appears to be two you regard them as different shapes. For example, you can have a compound with two trigonal planar shapes.

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Why does CF4 have greater ionic character than CH4?

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So, the bond angle in H 2 O is 104.5 degrees (from the textbook). On test 2, should we state that the bond angle for all angular molecules is 104.5 degrees or should we just say less than 120 degrees? To answer the question above, You would say it is less than 109.5 degrees 109.5 degrees is the pre...

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I don't think it matters too much, but I'd go with bent to be safe, but the names are interchangeable.

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The dipole moments do cancel out, the shape is symmetrical, and the surrounding atoms are the same. Their dipoles point in the same direction, so they should cancel out making CCl4 nonpolar.

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Will a difference in electricity always mean that there is a dipole moment?

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Yes!

The stronger the bond the higher the dissociation energy.

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What are the main differences between Dipole- Dipole, London Dispersion forces, and Hydrogen Bonding?

How are these ranked in terms on energy?

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What is covalent character in an ionic bond?

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Why are large anions highly polarizable?

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Adding on,

P and D orbitals have a nodal plane, zero electron density (non-symmetric)
S orbitals have no nodal planes (symmetric electron distribution)

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does 3d have higher energy than 4s? can someone explain why/why not?

Thanks!

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Electron affinity is the energy released when an electron is added, while electronegativity is the tendency of an atom to attract electrons towards itself in a molecule of a compound.

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I believe that often times carbon prefers covalent bonds (sharing electrons)

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You know that n=1 is the final because the electrons are dropping from a higher energy level (initial) to the Lyman series, n=1, which is a lower energy level and the final state.

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Ionic bonds involve the transferring of electrons from a metal to a nonmetal.
Covalent bonds involve non metals sharing electrons to form covalent bonds.

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I believe this has to do with the larger size of period 3 elements and how they are able to accommodate more bonds.

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In resonance structures,
the electrons are delocalized. This means they are more spread out and evenly distributed.

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I don't know if I understand your question completely, but a cation is a positively charged molecule, therefore electrons have been removed, which is why it is positive. In an anion, electrons are added and to a molecule increasing the negative charge, making the molecule negative. When figuring out...

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They are more stable because the electrons are delocalized.
Rather than being in a single lewis structure, they are more spread out and not bounded to a single bond.
This lowers the energy of the molecule, stabilizing it.

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I heard others say that their TA said it covers chemical bonding and quantum topics

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Can someone explain why s has no nodal plane? thanks!

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I agree with what was said above.

The Principle quantum level is the shell or energy level of an electron at ground state. At ground state electron's aren't excited and jumping energy levels.

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In the Heisenberg equation, what number would you plug in for delta X? and what does X stand for?

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When the energy of the photon matches the energy of an electron that photon is emitted or absorbed.

when a high energy electron drops to lower energy level, the difference in energy is given off as a photon.

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Is velocity usually in nm or m? does it matter when using the equations if the question doesn't specify units?

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A good tip to remember when converting units is to make sure they cancel until what you want is left. Set them up as ratios so that when you multiply terms the top and bottom cancel.

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Magnetic fields are produced by electric currents. They are dipolar, meaning they have a north and south magnetic pole. Both electric and magnetic fields are made of photons.

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The empirical formula can be viewed as the smallest ratio of the molecular formula. If the molar mass of the empirical formula is the same as the molar mass of the molecular formula given in the question then they are the same.

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A photon has the properties of both a wave and particle, a quantum doesn't. The photon is the quantum of electromagnetic radiation, or the basic unit of light. Quantum can be described as a measure of quantity but a photon is not about a measure of quantity. A photon is quantum but not all quanta ar...

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The N=1 is known as the ground state. The gap between N=1 and N=2 is the largest, meaning it has the largest release of energy. The ultraviolent region is the largest release of energy.

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I make sure my sigifigs are consistent all around. But if the problem gives a mass with specific sigfigs, I would try and match those.

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Combustion refers to "burning."
In combustion reactions, oxygen is always a reactant that will yield carbon dioxide and water.

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I ordered the elements as they are listed in the book. So, C, H, N, then O.

This is also the order the book has in the answer key.

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The molar mass of elements and compounds can be found from the periodic table.

For example:

C: 12.01g
O: 16.00g

CO2: 12.01g + 16.00(2) = 44.01g

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When you are asked to convert to formula units, atoms, or molecules, use avogadro's number.

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How would you calculate the amount of excess BrF3?

I understand how to calculate the moles of each product left, but how would I calculate the moles of excess reactant?

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