CHEMISTRY COMMUNITY

Toru Fiberesima 1L

What is meant by approximated concentrations for pre-equilibrium reaction mechanisms? How does this differ from the steady state? How are intermediates involved?

Toru Fiberesima 1L

What is the relationship between rate constant and equilibrium constant?

Toru Fiberesima 1L

Balance the same as an acidic solution, just add an OH- to balance out every H+. If there are H+ and OH- on the same side, add them to form H20.

Toru Fiberesima 1L

The average rate is obtained by taking the slope of the line connecting any two points on the curve during that period. Ie amount of change/time taken. The instantaneous rate is obtained by taking the slope of the line tangent to the curve at a given time (t). The instantaneous rate is essentially t...

Toru Fiberesima 1L

A reaction is zero-order if concentration data is plotted versus time and the result is a straight line.

Toru Fiberesima 1L

A reaction which is made first order by increasing or decreasing the concentration of a reactant is a pseudo first order reaction.

Toru Fiberesima 1L

Include H+ in cell diagrams when it is used to balance out the H2O on the opposite side of reaction

Toru Fiberesima 1L

The average rate is obtained by taking the slope of the line connecting any two points on the curve during that period. Ie amount of change/time taken. The instantaneous rate is obtained by taking the slope of the line tangent to the curve at a given time (t). The instantaneous rate is essentially t...

Toru Fiberesima 1L

Is there a way to use cell potential to calculate Ka without using Nernst? Can you go about this by finding Ecell, using that to find dG and then solving for K usuing -RTlnK?

Toru Fiberesima 1L

How would you predict the effect of changes in concentration of reactants and products on the cell potential?

Toru Fiberesima 1L

In a galvanic (voltaic) cell are the cathode and anode the same as in an electrolytic cell?

Toru Fiberesima 1L

Cations (positively charged molecules) gain electrons from the cathode, which is where reduction takes place. Contrarily, anions (negatively charged molecules) lose electrons at the anode, which is where oxidation takes place. Remember OIL RIG. Electrons always flow from the anode to the cathode or ...

Toru Fiberesima 1L

H2O and H+ are used to balance out the numbers of oxygen and hydrogen atoms in the reaction, look at 14.1 in textbook for an example

Toru Fiberesima 1L

Wondering how much the second test will cover, up to where in the textbook/homework problems and how far into electrochemistry

Toru Fiberesima 1L

Exergonic processes release energy. The change in Gibbs free energy (ΔG) is a negative value because energy is lost,
whereas an endergonic processes absorbs energy and their products are of greater free energy than the reactants.

Toru Fiberesima 1L

Standard state being 1atm and at 25°C. The standard Gibbs free energy of formation of a compound is the change of Gibbs free energy that occurs when 1 mole of a substance in its standard state is formed from its constituent elements which are also in their standard states

Toru Fiberesima 1L

The Ecell value is obtained from the two half reactions or the balanced chemical equation. Ecell is E(cathode) minus E(anode). For deltaG to be negative, which indicates that the reaction is a spontaneous one, E cell must be positive.

Toru Fiberesima 1L

Recall that dU=q+w. For an isothermal expansion q=-w. Also, temperature does not change (hence isothermal), therefore q=0. If q=0 then w=0. Thus, dU=0+0=0.

Toru Fiberesima 1L

W for reversible isothermal expansion of an ideal gas W=-nRTln(V2/V1)

Toru Fiberesima 1L

If a gas is compressed suddenly and irreversibly, treat it as a two step process where the dS from dT and dS from dV need to be accounted for. In this case, you would do dS=nCvln(T2/T1) if v was constant + deltaS=nRln(V2/V1).

Toru Fiberesima 1L

T=0 ie absolute zero does not necessarily mean that there is zero entropy. It does, however, mean that entropy and enthalpy will be at their minimum values.The Third Law of Thermodynamics states that as the temperature of a system approaches absolute zero, its entropy approaches a constant- for pure...

Toru Fiberesima 1L

Bond breaking is an endothermic process ie a process that requires energy. For endothermic reactions, the products of the reaction have a greater enthalpy than the reactants, and heat is absorbed by the system from its surroundings. Therefore, the delta H b must be positive because the energy is bei...

Toru Fiberesima 1L

They are essentially the same. It just depends which values you are given in the question, and which you can plug into the equation.

Toru Fiberesima 1L

no heat is transferred between two objects in thermal equilibrium

Toru Fiberesima 1L

Temperature of a substance does not change during a phase change. If heat is coming into a substance during a phase change, then this energy is used to break the bonds between the molecules of the substance.

Toru Fiberesima 1L

To break the bond, you have to fight against the bond, so energy is required in bon breaking. Potential energy is stored in molecules and this energy is released when bonds forms. Things tend to go to the lowest energy state possible

Toru Fiberesima 1L

Out of the various stresses, only temperature changes Kc

Toru Fiberesima 1L

According to Le Chatelier's Principles, how and why does temperature impact Kc?

Toru Fiberesima 1L

You should always refer to the question, and go by the number of sig figs used there.

Toru Fiberesima 1L

for Kc, you use the square brackets to denote concentration

Toru Fiberesima 1L

Do catalysts act as a stressor in a reaction? Do catalysts favor a particular direction ie the forward or the reverse?

Toru Fiberesima 1L

What would happen if one were to increase the temperature of a reaction, and why?

Toru Fiberesima 1L

What are the units for P=(nRT)/V? And what is the ideal gas constant?

Toru Fiberesima 1L

Technically temperature should have no real effect on pH, however, since water undergoes deconstruction of some sort from H2O -> OH- + H,
and there are 2x H. Since pH quantifies the quantity of H+ in a solution, the pH would be slighlty lower/more acidic in higher temperatures.

Toru Fiberesima 1L

If something has the ability to act as BOTH an acid and a base then it is amphoteric, so when looking at a reaction/equation, test if the compound has the ability to be a proton donor AND an hydroxide donor. One of the most common amphoteric substances out there is water as it behaves in this way.

Toru Fiberesima 1L

How do you calculate the difference between two pH values of the same acid, just diluted. 12.9 is an example of a question that asks you to do this.

Thanks

Toru Fiberesima 1L

ClO2+ has 4 different resonance structures so I am wondering if each structure would warrant a different molecular shape.

Thanks

Toru Fiberesima 1L

You can also use the principle quantum numbers of the element to determine how many electrons it can hold. Typically, the highest number of electrons that can fit in any given shell = 2n².

Toru Fiberesima 1L

Hydrocarbons often form structures like this, with carbon as the central atom and hydrogens branching off- for example benzene rings. So just predict such structures for molecules with multiple carbons and hydrogens.

Toru Fiberesima 1L

Dissociation energy is a measure of the strength of a bond. Therefore, it can be measured by breaking bonds, and recording how much energy was required to do so.

Toru Fiberesima 1L

electron density counts for both bonding and unshared electron pairs around the central atom

Toru Fiberesima 1L

The central atom is the atom that has the lowest electronegativity or the highest valence. You expand from there.

Toru Fiberesima 1L

For question 3.37, why would the answer be phosphorus specifically and not, say nitrogen, or any of the other period 3 elements. Would they not all work due to having 5 valence electrons. In general, how does one figure out an unknown element from a lewis structure?

Toru Fiberesima 1L

Seeing as the question asks for a maximum and a minimum oxidation number, can there be an intermediary oxidation number or must the answer be +7 and/or -1?

Toru Fiberesima 1L

If the work function of A is 6x10^-19 J per atom and the work function of B were let's say 7x10^-19, wouldn't you expect A to eject a slower electron than B if the same light source shines on both. Why is this NOT the case??

Toru Fiberesima 1L

Yes, all matter has both wave-like and particle properties- including protons and neutrons. The concept is just typically used with quantum mechanics due to the small scale because large scale matter has a wavelength that is far too short to be detected.

Toru Fiberesima 1L

Yes and we should know how to explain why the exceptions occur, for example because a full shell OR half full shell are most stable. Nitrogen's half full shell is what makes it more stable than oxygen, resulting in a higher ionization energy.

Toru Fiberesima 1L

If a proton is accelerated in a cyclotron to a very high speed that is known to within 3.0x10^2km*s^-1. So you know the speed, you can find out the momentum, but how do you find out the minimum uncertainty in the position.

Toru Fiberesima 1L

when we talk about the principle quantum number for a particle, we are referring to electrons

Toru Fiberesima 1L

The 4s shell is only lower in energy if there than 3d when there aren't electrons in 3d, which is why atoms lose the 4s electrons before they lose the 3d electrons. Those in the 3d shell would be the highest energy electrons due to the repulsive forces of electrons already in the 3d shell.

Toru Fiberesima 1L

electron affinity is the energy released when an atom acquires an electron (ie these would be negative values). So yes, a high electron affinity would mean the energy released when an electron is added would technically be very low.

Toru Fiberesima 1L

You would describe the magnetic quantum number (m) which labels different orbitals of a subshell including nodal planes ie symmetric density distribution or not

Toru Fiberesima 1L

I believe we should be able to identify and draw different orbital according to information given about the planes and quantum values (n,l and m)

Toru Fiberesima 1L

The orbital that hydrogen's electron is in is the 1s orbital, the 1 meaning that the electron is in the energy level closest (1st energy level) to the nucleus. If an electron is in a 2 orbital (2nd energy level) it just means that there is a greater chance that the electron will be further away from...

Toru Fiberesima 1L

The velocity of an electron that is emitted from a metallic surface by a photon is 3.6x10^3 km/s. No electrons are emitted from the surface of the metal until the frequency of the radiation reaches 2.50x10^16Hz. How much energy is required to remove the electron from the metal? I know you eventually...

Toru Fiberesima 1L

When you know the velocity of an electron, how do you then calculate the wavelength?
Thanks

Toru Fiberesima 1L

I'm wondering how you go about calculating the kinetic energy of an ejected electron when you are only given the speed at which it is ejected. What would you would put for mass of electron in the KE equation.

Thanks

Toru Fiberesima 1L

you would normally use grams unless the question uses or states otherwise or if the calculated number is very large, making it more convenient or logical to use kg. Typically, you'll be able to tell what is appropriate.

Toru Fiberesima 1L

I believe the aim was to observe how the transfer of energy from light to an electron in the metal results in the emission of said electron from the metal

Toru Fiberesima 1L

start by balancing the atoms with the highest number of atoms in the reaction. Typically you leave balancing oxygen and/or hydrogen until last

Toru Fiberesima 1L

you should always use the number of sig figs of the number with the lowest number of sig figs in the question and subsequent calculations

Toru Fiberesima 1L

Hi so n is moles, m is mass and M is molar mass. Thus, moles is equal to mass divided by molar mass. You would get the molar mass from the periodic table. Also, c is concentration, n (again) is moles and V is volume.Thus, concentration is equal to moles divided by volume of solution. In each equatio...

Toru Fiberesima 1L

Volume is equal to moles/concentration, so you would do 4.5x10^-3 mols divided by 0.278M.
Hope this helps

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