CHEMISTRY COMMUNITY

Srbui Azarapetian 2C

How do you know when to use the lewis structure of benzene with resonance between the 6 carbon bonds, versus using bond enthalpies of 3 single and 3 double carbon - carbon bonds?

Srbui Azarapetian 2C

What are the cases when we can use the molar coefficients in an equation as the order when writing the rate law, instead of the experimentally determined order? And what exactly allows us to assume that the coefficient is also the order?

Srbui Azarapetian 2C

Could you post the question that goes along with this question? Also, you do know T because the reaction happens at standard conditions, which is 298 K .

Srbui Azarapetian 2C

The two equations you use are 1: Cr2O7^2- + 14H+ + 6e- -> 2Cr^3+ +7H2O . E=1.33V 2: Cr3+ + 3e- -> Cr(s) . E=-.74V Notice that a sum of these after balancing the charges creates the overall equation. Since electric potential is not a state function, you have to use Gibbs Free Energy (delta G=-nFE) G(...

Srbui Azarapetian 2C

You basically solve this as you would a regular rate law with multiple steps. You cancel out the species/structures that are products in one equation and thus used as reactants in the others. These are your intermediates. The catalyst is not consumed in the reaction and is therefore present in the b...

Srbui Azarapetian 2C

You have to find the proportion of rate of the catalyzed reaction to rate of the uncatalyzed reaction. The rate is equal to the two Arrhenius equations, k=A*exp(-Ea/R*T). The activation energy (Ea) of the catalyzed reaction is 75/ 125 times the activation of the uncatalyzed reaction, which is (.60)....

Srbui Azarapetian 2C

The main component of this diagram bust be that the two Br's must be next to each other and the NO must be ejected together. The NO is written together because that is how the gas is released and not the N and O separately in the case of decomposition.

Srbui Azarapetian 2C

Zero order means that the rate of the reaction is independent of the concentration of the species.This is why it is disregarded in the rate law and therefore also in finding the order of A and B.

Srbui Azarapetian 2C

Using experiments 3 and 1, the concentration of A remains as 1.25 and the concentration of C remains as 1.25 also. The important thing to note here is not that both A and C have a concentration of 1.25 but that A's and C's concentrations stay consistent separately. 50.8/8.7 is 5.839 and the ratio of...

Srbui Azarapetian 2C

Typically, the rate law would come from the slow step so, R=k2 [HOCL][I-]. However, HOCL is an intermediate, so it needs to be expressed in terms of other products and reactants of the other fast reactions. Using the equation ClO-+H2O--->HClO+OH-, K = [HOCL][OH]/[OCL]. From this equilibrium equation...

Srbui Azarapetian 2C

The rate constant changes with temperature because the rate of a reaction is dependent on temperature. This has to do with activation energy and the likeliness of a reaction happening because a greater presence of reactants (concentration) or a higher temperature, meaning more kinetic energy, which ...

Srbui Azarapetian 2C

It is series of chemical elements arranged in order of their standard electrode potentials. It shows the order in which metals replace one another from their salts. Basically a list of reduction half- reactions.

Srbui Azarapetian 2C

You can also think of it as energy difference between the transition state of a reaction and the ground state of the reactant or the difference between transition states and intermediates.

Srbui Azarapetian 2C

You would add the H20 first to balance the oxygens, then balance hydrogens using H+, and after balancing the charges, convert the H+ to H20 by adding OH¯ to both sides. The side with the H+ will determine how many hydroxide to add.

Srbui Azarapetian 2C

The equation must be reversed because the original oxidation reaction is Au3+(aq) + 3e- -> Au (s). This must be reversed into Au (s) -> Au3+(aq) + 3e- so that the Au 3+ ends up in the products side of the cell reaction given in the problem, Au3+ (aq) -> Au(s) + Au3+ (aq).

Srbui Azarapetian 2C

What would would be a scenario when to use the specific heat capacity of ice, instead the usual 4.184 for water?

Srbui Azarapetian 2C

I don't think we have to derive them, but we should understand where the equations come from and exactly why and how, conceptually, we can manipulate equations in such ways.

Srbui Azarapetian 2C

You only use 3/2 R if the ideal gas is at constant volume, which in this case it is not.

Srbui Azarapetian 2C

When delta G is zero, that means the system is at equilibrium and has no available energy. At boiling point it is zero because there is no change in temperature or pressure, therefore, by delta G = (delta H of vaporization) - (T of vaporization) X (delta S of vaporization) =0. It is also zero at the...

Srbui Azarapetian 2C

You would calculate the entropy of formation of one mole of the substance. If $\Delta S$ is positive, then the substance is more stable at higher temperatures. If it is negative, it is less stable.

Srbui Azarapetian 2C

The equations that basically sum up these relationships are $\Delta G$ (o) = -RTlnK and G = G(o) = RTlnP

Srbui Azarapetian 2C

The change in entropy can be negative, and when this is the case, you can think of it as a system becoming more ordered. An example would be of condensation, in the transition from a gas (high entropy state) to a liquid (low entropy state).

Srbui Azarapetian 2C

Because the six resonance - stabilized bonds hold more energy (3108 kJ) compared to the 2880 kJ of energy in the isolated bonds, they are more difficult to break.

Srbui Azarapetian 2C

In the forward reaction if entropy was positive and enthalpy negative, the reaction is spontaneous at all temperatures. In the case of the same reaction, except the reverse, the reaction would have negative entropy and enthalpy positive, which is the most unfavorable set of conditions, meaning the r...

Srbui Azarapetian 2C

To add to the previous answer, the spontaneity, or Gibbs free energy depends on entropy and enthalpy. Positive entropy and negative enthalpy means the reaction is spontaneous at all temperatures. Positive entropy and enthalpy means the reaction is spontaneous at high temperatures. Negative entropy a...

Srbui Azarapetian 2C

Use the equivalency of the ideal gas constants, 8.314 J K /mol = .08206 L atm / K mol . the - 1.48 is in L atm so through dimensional analysis of multiplying by 8.314 J K /mol over .08206 L atm / K mol , this should result in - 150 Joules.

Srbui Azarapetian 2C

The reaction for 1 mol of gaseous water is H2(g)+1/O2(g)->H20(g). The question asks for to find the enthalpy of formation of liquid water. This involves use of the equation: Enthalpy of formation of liquid water = Enthalpy of formation of gaseous water- Enthalpy of vaporization to account for the ph...

Srbui Azarapetian 2C

What are all the elements for which need to know the standard states of and that their enthalpy of formation of its most stable form is zero? (ex. O2, N2)

Srbui Azarapetian 2C

The w=-nRTln(V2/V1) equation is used for reversible expansion. This means that the pressure is continually changing.

The w=-P*deltaV is sued for irreversible expansion. This is in situation with a constant external pressure.

Srbui Azarapetian 2C

A closed system allows heat transfer, but does not allow mass transfer. An isolated system allows neither heat nor mass transfer.

Srbui Azarapetian 2C

Note that q is + 5.50 kJ as it is the amount of heat energy being gained. The work equation being used in the problem is w = -P(ext) x delta V. First convert the 750 torr to atm by dividing it by 760. Multiply the resulting .98684 atm of pressure by the change in Liters of volume (1.846-.345=1.501)....

Srbui Azarapetian 2C

What does it mean for a molecule to have delocalized pi bonding? How do we observe this given the structure?

Srbui Azarapetian 2C

Percentage deprotonation represents the ratio of the concentration of dissociated [H+] to the concentration of the undissociated [HA], or in other words the percentage of the initial acid that creates H3O+/H+ and it's conjugate base.

Srbui Azarapetian 2C

When rounding off significant figures for pH, do we start counting significant figures after the decimal point or the entire number. For example is ph= 5.42 2 significant figures or 3?

Srbui Azarapetian 2C

I think it would be helpful to know for the final in order to know which method to use to find the pH, since strong acids completely disassociate and weak acids only partially disassociate.

Srbui Azarapetian 2C

A Bronsted acid is a proton donor, and a Bronsted base is a proton acceptor. A Lewis acid is an electron acceptor, and a base is an electron donor.

Srbui Azarapetian 2C

Although you are no explicitly told to ratio of reactants to products, you can deduce this information from the provided graph. Because use the C and B start from 0, you can assume that they are both the products. The A stats from a positive number, which means it was previously present, so it is th...

Srbui Azarapetian 2C

Electron geometry describes the arrangement of electron groups. Molecular geometry describes the arrangement of atoms, excluding lone pairs. For example, in the case of a trigonal planar shape as defined by electron geometry, there are three bonds. If atoms are bonded at all three locations, the mol...

Srbui Azarapetian 2C

I think 107.5 is the exact measurement of the bond angle, whereas the use of "slightly less" means that you just estimate the bond angle through the electron placement and repulsion.

Srbui Azarapetian 2C

HOCO is the same order as how the elements are aligned in the lewis structure. First you count the number of valence electrons: 1 for Hydrogen, 2 x 6 for Oxygen, and 4 for Carbon. This equals 15 electrons total to be shared. Then begin by drawing a single bond between all the atoms, resulting in H-O...

Srbui Azarapetian 2C

In the case of coordination compounds, OH2 is preferred when the oxygen is what is bonding the metal central atom. In this case, the lone pairs on the O are the ones binding to the central atom to the left of the water molecule. H2O is preferred to show that the lone pairs on the O are binding to th...

Srbui Azarapetian 2C

A T shape has 3 bonds, and 2 lone pairs. An example of this is ClF3.
However, a trigonal planar shape has 3 bonds and 0 lone pairs. An example is BF3.
A trigonal pyramidal shape has 3 bonds and 1 lone pair like NH3.

I think the key difference here is the lone pairs.

Srbui Azarapetian 2C

You would count the total number of electrons in the s-, p-, d-, and f- subshells which is 32 electrons. Then, since the question is only asking for electrons with ms = +1/2, you would divide 32 in half to get your answer of 16 electrons. That is the answer I got also, but the answer from his old c...

Srbui Azarapetian 2C

How would you go about counting the maximum number of electrons in atom with n=5 and ms=+1/2?
Would you only go up to the f subshell?

Srbui Azarapetian 2C

Is there a reason I should know for why this rule works? The reason the criss-cross method outlined above works is because it balances charges. For example in magnesium Nitride, magnesium has a charge of 2+ and nitride 3-. Therefore, three magnesium ions are needed to balance out two nitrogen ions....

Srbui Azarapetian 2C

I know that atomic radii decreases from left to right across a period as the effective atomic number increases, and they increase down a group as successive shells are occupied. Also that cations are smaller than their parent atoms and anions larger. However, when comparing for example, Cs+1 and Ba,...

Srbui Azarapetian 2C

Is this the same answer to the question of why the second ionization energy of an atom is always higher than the first? Ionization energy is a measure of how difficult it is to remove an electron, so the second ionization energy is usually considerably larger, especially in the case of a Group 2 el...

Srbui Azarapetian 2C

Atomic radii generally decrease from left to right across a period as the effective atomic number increases, and they increase down a group as successive shells are occupied. If the two ions are in the same group, the smaller ion will be the one that lies higher in the group, because its outermost e...

Srbui Azarapetian 2C

This can be summed up through the photoelectric effect. An electron does not usually have enough energy to move up quantum states and orbitals on its own. It has to somehow be given the energy to do so, which we can observe directly through the experiment. The light gives energy to the electron and ...

Srbui Azarapetian 2C

De Broglie's equation states that wavelength is equal to Planck's constant, h, divided by mass times velocity. To find the mass of helium for a single atom, you could divide the atomic mass, given in the periodic table, by Avogadro's number. 4.00 g/mol of Helium divided by 6.022 x 10^23 mol-1 is equ...

Srbui Azarapetian 2C

The equation that would be used for finding the electronic energy levels is E=-hR/(n^2). The second part of the question is asking if the calculated number resulted from using this equation are going to correspond to real life experiments, of which mass spectroscopy is one of those experimental meth...

Srbui Azarapetian 2C

what exactly is the relationship between quantized energy and the n energy levels? I am a little confused In an atom, for example hydrogen, the electrons can only exist in specific energy states, which we associate with the "n energy levels", and they are quantized because they are set, t...

Srbui Azarapetian 2C

The first step to write a balanced equation. This would be H2A + 2XOH --> 2H20 +X2A Then with the given masses and molar masses, divide the mass by the molar mass for each of the reactants. For H2A : 1.20g/168gmol-1 = 0.00714 mol of H2A For XOH: 1.00g/125gmol-1 = 0.00800 mol of XOH Then you multiply...

Srbui Azarapetian 2C

Just a heads-up to anyone going over the online module questions, For the question that asks, "According to the following equation, 0.750g of C6H9Cl3 is mixed with 1.000 kg of AgNO3 in a flask of water. A white solid, AgCl, completely precipitates out. What is the mass of AgCl produced?" T...

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