CHEMISTRY COMMUNITY

michelle

Do we always use unit in bar when calculating partial pressure equilibrium constants?

michelle

Will you post the answers here as usual?

michelle

The rule for reducing power is that the more negative the standard potential E is, the greater reducing power.

michelle

I think the question will specify. If they are asking for formation rate, they will explicitly say which species. The rate law equals unique rate. You can recall from the integral rate law process.

michelle

rate of formation is approached by unique rates, while experimental rate law is directly from the data (remember the tables?)

michelle

I think no. You can only ensure a decay reaction as first order reaction when the half-life is a constant.

michelle

It implies the reaction mechanism and is related to molecularity.

michelle

There is a general formula: if x is the overall order of the reaction, the unit of k is (M)^(1-x)/s. M is mol/L

michelle

Max potential is related to delta G by delta G= -nFE

michelle

By the stochemiistry coefficients, and the unique rates.

michelle

Yes. Unique rate is spontaneous rate, which will definitely change with time. But we usually talk about the initial rate.

michelle

In this reaction, Cl2 is both oxidized and reduced. Try to identify the oxidation number of each "Cl" in this reation.

michelle

The total delta G of a reaction equals the total delta G of products minus that of all the reactants. At equilibrium, there is no difference between the delta G of the reactants and the products, so that total delta G equals 0.

michelle

Gibbs free energy is the available energy that can do useful work. They are related by the equation delta G= delta H- T*delta S.

michelle

Actually, it should be G=G knot + RTlnQ. It implies that the reaction is not at equilibrium.

michelle

Like the concept in enthalpy. Delta G knot is the change in G under standard conditions (1 atm or 1 M). Delta G can be the change of free energy of the whole process(reaction).

michelle

I think the book wrote that way because we usually can find out S(system) so that we relate that to S(surroudings).

michelle

In a reversible system, energy lost through doing work by the system will be replenished to the system through inputting heat. It is very efficient and slow. Reversible system usually is isothermal, which means no temperature change.

michelle

For an irreversible system, work is done under constant pressures and energy is lost as heat. For a reversible system, each energy lost by doing work will come back to the system as heat, and it is more efficient.

michelle

Maybe it is free expansion. The internal energy doesn't change because as long as there is no volume change no work can be done. The system expands due to an increase in entropy.

michelle

Usually, questions will give initial and final volumes or the change in height.

michelle

Our TA says you just need to examine the giver conditions to choose methods. But definitely remember using bond enthalpy is the least accurate.

michelle

I think enthalpy can be calculated under any condition, but maybe most questions will give a constant pressure, just temperature.

michelle

Not really. I think we only are supposed to know the standard state.

michelle

Pure liquid and solid are naturally considered as in their standard state. The standard state for a solution is defined as 1 M. The standard state for an element is its most stable phase at 1 atm.

michelle

Breaking bonds requires energy, resulting in positive enthalpy while forming bonds release energy, resulting in negative enthalpy. In other words, the enthalpy change made by reactants is positive while that made by forming products is negative.

michelle

Buffer solution usually consists of a pair of conjugate weak acid and base. The variation in pH results from the Kc of acid/base.

michelle

It depends on how you decrease the pressure. You can either increase the volume or introduce other unrelated gases.You can then relate the change in pressure with the change in moles.

michelle

No. Water is only considered in the calculation when it is in gas phase.

michelle

The is no keyword I think. But it always works in equilibrium problems.

michelle

Not always. For instance, when the pressure is increased by adding inert gas and the container is not changed, the volume stays the same.

michelle

Yes...

michelle

NO3 is the conjugate base for strong acid that will get a proton from water to form OH- in the solution.

michelle

You are supposed to remember all the strong acid and bases, according to a UA. Then the rest are all weak ones.

michelle

You need to tell it from Lewis structures because the charges of ions stem from formal charges which also depend on the valence electrons of the atoms that from the ion.

michelle

Amines are weak bases, becasue they are proton acceptors by the definition of Bronsted base and they are lone pair donor by the definition of Lewis base.

michelle

You can usually know the overall charge of the complex from the question. Utilize your knowledge for the charges of the most common ligands to calculate the ones unknown.(usually only one)

michelle

Chelate is the complex containing a ligand that forms a ring of atoms that includes the central metal atom. Because a ring structure is formed, I think the complex is more stable.

michelle

Electron density refers to all regions that have electrons, which includes lone pairs. However, when we name shapes, only atoms are counted.

michelle

Hybridization allows you to figure out how bonds are formed by displaying the electron regions in the real case that is most stable for the lowest maintaining energy.

michelle

In most cases, an increase in molecular size attributes to an increase in the size electro regions of the atoms that construct the molecule, so an increase in size will make the intermolecular interaction stronger.

michelle

I remember in the lecture this came after the discussion about bond angles. When lone pairs are involved, VSEPR can only predict the bond angles within a interval but cannot predict the angle precisely.

michelle

I think it became complicated from 5 bonding regions because the increasing chance of lone pair getting involved. You can simply first ignore the difference between bonded and lone pair regions and regard them all as atoms to get the intuitive shape and remove the atom to reconsider if it is a lone ...

michelle

You can simply distinguish them with the number of atoms as the above posts say, or imagine the shape based on Lewis structures. Pay attention to lone pairs.

michelle

It was not clarified on the lecture but in the discussion, our TA cataloged it to diple-diple interactions.

michelle

The first step is drawing Lewis structure and see how the bonded pairs electrons repel each other, according to VSEPR. For example, BeCl2 is linear because there are two bonded pairs of electrons around the central atom Be, while BF3 is trigonal planar because there are 3 bonded pairs around the cen...

michelle

Lewis structure illustrates 2-D structures while the molecular shape is 3D. So it does not necessarily need to correspond to each other. Lewis structures only need to give a guideline to molecular shapes.

michelle

Only elements after period 3. For instance, elements in period 3 has unoccupied d orbitals which enable them to expand their electro clouds.

michelle

Sulfur has a higher effective nuclear charge which can attract electrons more strongly.

michelle

Do you mean elements that are at diagonal positions on the periodic table have similar properties.

michelle

I think so. But there is only 4 of them.

michelle

They are not the same. Electron affinity has no clear periodicity, and elements on the top left of the period table tend to have higher electro affinity. On the otehr hand, ionization energy display clear periodicity.

michelle

Ionization energy has periodicity.

michelle

You can use the one written in the textbook, which the professor didn't cover in lecture. That one is more straight forward to calculate the problems you mentioned. But he also said that he prefer students to use the equation he covered, which will also be used in exams.

michelle

With the given delta x, which is the diameter of the atom, we can calculate the minimum delta momentum with the Heisenberg uncertainty principal (the equation). Because the minimum velocity calculated then is larger than the velocity of light, which should be the largest velocity possible, the model...

michelle

The question will usually clarify which variable it is asking, so there is no particular sequence in solving such problems.

michelle

That should be kg. We use SI units in all equations.

michelle

Threshold energy is the least energy needed to remove an electro of certain metal. Different metals have different threshold energy.

michelle

I think we should at least remember the range of UV and visible light.

michelle

I think yes. Only in that way you could find the ratio of moles.

michelle

Aqueous solution is the solution that the solvent is water. I actually think the chemical equations are designed to show the process of the experiments. To better represent the process, the states of reactant can help clarify the experiment.

michelle

In one step-reactions, there will only be one limiting reactant. It is possible that all the substance involved in a reaction is completely consumed, in which there are no limiting reagents or all the reactants are limiting.

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