CHEMISTRY COMMUNITY

Karina Kong 2H

What makes a step the rate determining step?

Karina Kong 2H

Could someone explain why there are different units for each order?

Karina Kong 2H

Could someone explain how the order of a reaction affects the graph?

Karina Kong 2H

Could someone explain what a pseudo rate law is?

Karina Kong 2H

For n in the equation Delta G=-nFE, how do you know how many moles you need?

Karina Kong 2H

If given to E potentials, is the higher E potential the cathode?

Karina Kong 2H

For the most part, Hydrogen will be +1, Oxygen is -2 except in H2O2 it's -1, and halogens are -1.

Karina Kong 2H

How do you write the cell diagram if an element is aqueous on both sides?

Karina Kong 2H

How do you find the anode concentration with the Nernst equation?

Karina Kong 2H

Any type of material can be used as long as it transfers positively charged ions to one cell and negatively charged ions to the other cell.

Karina Kong 2H

Other helpful ways to find oxidation numbers is that in most cases, hydrogen will always be +1, oxygen will be -2, and halogens will be -1

Karina Kong 2H

You balance the equation with H+ in an acidic reaction and H2O to balance the O2 in that same reaction. If the reaction is basic, you balance it with H20 and OH

Karina Kong 2H

It's just a way to distinguish between a positive and negative charge. It also helps with practicing good notation

Karina Kong 2H

What determines the difference between zero, first, and second order?

Karina Kong 2H

On the left you write the anode and its two states. The two lines in the middle represent the salt bridge. The reason why the salt bridge is there is that so it can neutralize the charge since when the cell is running all the electrons are moving to the cathode. On the right of the salt bridge (two ...

Karina Kong 2H

How do we balance redox equations in a basic solution?

Karina Kong 2H

What is the purpose of a salt bridge?

Karina Kong 2H

When do you change the sign of the value of the anode or cathode?

Karina Kong 2H

If the charge on the atom increases it is being oxidized. If the charge on the atom decreases it is being reduced.

Karina Kong 2H

In PV=nRT, if you have to solve for the number of moles and are given the initial and final volume which do you use?

Karina Kong 2H

Why do we do reactants minus products for mean bond enthalpies rather than vice versa like the other methods of calculating enthalpy?

Karina Kong 2H

Why does Delta U = 0 when the system is isothermal?

Karina Kong 2H

Could someone explain when each of these three variables (Delta S of universe, Delta S of system, and Delta S of surroundings) is equal to 0?

Karina Kong 2H

When do we use Cv vs Cp?

Karina Kong 2H

When do we use Cv vs Cp?

Karina Kong 2H

Why is heat capacity an intensive property?

Karina Kong 2H

I get that reversible reactions change infinitesimally, but why does it have greater changes in internal energy than irreversible reactions?

Karina Kong 2H

Why is the heat capacity for constant pressure greater than the heat capacity at constant volume?

Karina Kong 2H

Could someone explain the relationship between work and volume? I'm still a little confused. Thanks!

Karina Kong 2H

Why is enthalpy in terms of constant pressure, but internal energy is in terms of constant volume?

Karina Kong 2H

You can also add and subtract state functions.

Karina Kong 2H

Entropy is the amount of energy that is unavailable to do work on the system. Entropy never decreases, but rather increases or stays the same. In relation to heat, when you heat a system, you increase its entropy since more energy excites the molecules.

Karina Kong 2H

An example of a closed system is a pot with a lid on top of a stove.

Karina Kong 2H

As pressure increases, so does enthalpy (and vice versa).

Karina Kong 2H

How do you account for phase changes when calculating enthalpy?

Karina Kong 2H

Which method of calculating enthalpies is the most accurate?

Karina Kong 2H

How do you know if a reactant or product is at its standard state?

Karina Kong 2H

Can someone explain Hess's Law?

Karina Kong 2H

When a reaction becomes exothermic, heat becomes a product of the reaction. This shifts the reaction towards the reactants, making the reverse reaction favored.

Karina Kong 2H

Could someone explain how autoprotolysis of water leads to Kw?

Karina Kong 2H

Since weak acids do not dissociate as much as strong acids, there is a smaller concentration of H+ ions in weak acids, leading to a higher pH.

Karina Kong 2H

pKa gives determines whether or not the acid is weak or strong (the properties of that specific compound) while pH determines whether it is acidic or basic.

Karina Kong 2H

Why do we approximate x when Ka is small in the equilibrium equation?

Karina Kong 2H

Inert gases also do not affect the partial pressures of the other gases in the container, therefore not affecting the constant.

Karina Kong 2H

Q is used when the equation is not at equilibrium. We can use Q to determine whether or not the equation will favor the reactants or products.

Karina Kong 2H

A sample of ozone, O3, amounting to .10 mol, is placed in a sealed container of volume 1.0 L and the reaction 2 O3(g) --> 3 O2 (g) is allowed to reach equilibrium. Without doing any calculations, predict which of the following will be different in the two containers at equilibrium. Which will be the...

Karina Kong 2H

Why aren't solids and liquids included in the equilibrium equation?

Karina Kong 2H

The ideal gas law is only valid when there is low pressure and high temperature.

Karina Kong 2H

Why do cations that come from weak bases act as strong acids?

Karina Kong 2H

How do bond length and resulting anion stability determine the strength of weak acids? And when do you use one over the other to determine it?

Karina Kong 2H

LDFs are a type of Van der Waals forces. LDFs are present everywhere because they occur when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles.

Karina Kong 2H

When do you use bond strength over electronegativity (and vice versa) when finding out which acid is stronger?

Karina Kong 2H

What does it mean a compound is more electron withdrawing and how does that have to do with acidity?

Karina Kong 2H

The stronger the acid, the weaker its conjugate base. The stronger the base, the weaker its conjugate acid.

Karina Kong 2H

The extent to which we need to calculate it is just plugging in the concentrations in the equation Ka = ([H+][A-])/[HA]. If the Ka is a large constant, that means the molecule dissociates quicker and is therefore a stronger acid.

Karina Kong 2H

pKa = -logKa. pKa is just the negative logarithm of the acidity constant.

Karina Kong 2H

Could someone explain what autoprotolysis equilibrium is?

Karina Kong 2H

An example that is in the textbook is that aluminum oxide is amphoteric because it reacts with both acids and bases, but it has no hydrogen atoms to donate as protons so it is not amphiprotic.

Karina Kong 2H

What does "mixing atomic orbitals into new hybrid orbitals" mean?

Karina Kong 2H

Do we need to know the biological functions of the transition metals (Cr, Fe, Co, Mn, Ni, Cu, Zn) he mentioned in lecture?

Karina Kong 2H

Cis molecules are polar while trans molecules are nonpolar.

Karina Kong 2H

How does the fact that TMs having many oxidation states make TMs good for electron transfer?

Karina Kong 2H

Could someone explain what a chelate complex is?

Karina Kong 2H

How do you find the shape of the molecule if there are two central atoms?

Karina Kong 2H

Why are single, double, and triple bonds treated as equivalent regions of electron density?

Karina Kong 2H

What is the difference between lone-lone pairs, lone-bonding pairs, and bonding-bonding pairs?

Karina Kong 2H

What does the phrase "polar molecules interact with an electrostatic potential" mean?

Karina Kong 2H

The VSEPR formula is AXnEn where A is the central atom, X represents how many atoms are bonded to the central atom, and E represents the number of lone pair electrons

Karina Kong 2H

In what case would we use the interaction potential energy equation?

Karina Kong 2H

Why does CH4 have a lower boiling point than CCl4?

Karina Kong 2H

What's the difference between ion-dipole and induced-dipole forces?

Karina Kong 2H

In addition, rod-shaped molecules are closer and have more surface area touching which produced a stronger interaction.

Karina Kong 2H

The more surface area that's touching, the stronger the interaction. This is why rod-shaped molecules are stronger than spherical molecules.

Karina Kong 2H

Can someone explain the connection between distortion, polarizability, and covalent character?

Karina Kong 2H

Could someone give an example of a coordinate covalent bond?

Karina Kong 2H

There are also less lone pair electrons that make that pull the atoms away from each other when there are more bonds. Therefore, more bonds correlates with higher strength.

Karina Kong 2H

Can someone explain how covalent bonds can have increasing ionic character? Thanks!

Karina Kong 2H

In general they are both important. But regarding formal, you'd want to spread it out than have it condensed into one atom/side.

Karina Kong 2H

Electrons usually repel each other so spreading them out (meaning they are delocalized) results in a lower energy state and more stability.

Karina Kong 2H

If the last electron that enters is spin up then it is +1/2. If the last electron that enters is spin down then it is -1/2.

Karina Kong 2H

The trends for both electronegativity and ionization energy are the same. Electronegativity is the the tendency for an atom to attract an electron. With a higher electronegativity, there is usually a higher ionization energy.

Karina Kong 2H

The second ionization energy is always higher because when you remove the first e-, it becomes a cation which is positively charged. That positive charge is then more attracted to the negative charge of the electron, making it harder to pull a second electron away.

Karina Kong 2H

I think it's easier to think about how ionization increases across a period and decreases down a group. When you go from left to right, the atoms have an increasing amount of protons which results in a higher nuclear charge, pulling in the e- tighter. When you go from top to bottom, you are adding s...

Karina Kong 2H

In order to achieve the lowest energy state and increased stability, the electrons need to have parallel spin.

Karina Kong 2H

There are four subshells. Since n=4, l can only be four different values which are 0,1,2, and 3 which correspond to s, p, d, and f.

Karina Kong 2H

I think Dr. Lavelle just wanted us to conceptualize the equation. Q1 and Q2 represent the magnitude of the charges while r represents the distance between the two particles. If the Ep comes out as negative, that means the particles are attracted to each other since they are opposite signs. If Ep com...

Karina Kong 2H

The number 4 in 4p is just the principal quantum number and do not affect the amount of orbitals there are. Therefore, just look at what type of sub-shell it is.

Karina Kong 2H

Could someone explain the difference between probability vs probability density? Thanks!

Karina Kong 2H

Frequency is directly related to the amount of energy of a photon. The intensity determines the amount of photons emitted. Therefore, it doesn't matter how intense the light is if the frequency is low since it won't reach the threshold energy.

Karina Kong 2H

If you look at the equation E=hv, you can see that only the frequency and not wavelength/intensity affects E. Therefore, increasing the intensity does not increase the kinetic energy of the electrons

Karina Kong 2H

Could someone explain what black body radiation is? Thanks

Karina Kong 2H

I know that the Balmer series is the visible region and that the Lyman series is the UV region, but are there any other differences between them?

Karina Kong 2H

Threshold energy is the amount of energy that needs to be put in, while the work function is the frequency that is required to reject an electron. However, mathematically they are both the same.

Karina Kong 2H

It is best to try and not round until the end, otherwise it could offset your value by a few decimal points. Once you reach the end, round to the least amount of significant figures in the problem.

Karina Kong 2H

The reason why the two 0's right after the decimal are not significant are because they serve as place holders. If you were to write this in scientific notation, those 0's would be gone. Therefore, you need to add 0 at the end to have 5 sig figs.

Karina Kong 2H

If there is a 0 at the end of the number, or multiple 0's, those 0's are not significant. For example, in the number 200, there is only one sig fig which is 2. If there is a decimal point after the 200, such as 200., there would be three sig figs. If there is a 0 in the middle of the number such as ...

Karina Kong 2H

Accuracy is how close the samples are to the correct value. Precision is how close the samples are to each other.

Karina Kong 2H

First you would convert KMnO4 into mols, then divide by 150mL to find the molarity (M1). Since you are extracting 20mL of that solution, that will be your V1. Now you are trying to find M2 if the solution is placed in a 250 mL beaker (V2). Plug in the values using M1V1=M2V2 and you should get the an...

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