CHEMISTRY COMMUNITY

Irene Zhou 1E

The order of the reaction just shows if the rate of the reaction is dependent on the concentrations. Thus, if one reactant is zero order, that means the concentration of that reactant does not affect the rate of reaction.

Irene Zhou 1E

We have to consider the rate of disappearance for the reactants so I think I would use the mol-to-mol ratio to calculate how much reactant disappeared.

Irene Zhou 1E

You would have to use the half life formula for a first order reaction. You could also use it for parts a and b but it may be easier to just calculate how many half-lives elapsed.

Irene Zhou 1E

The slowest step is the rate-determining step.

Irene Zhou 1E

A concentration cell is a type of galvanic cell in which the two half-cells are made up of the same type of solution, only different in concentration. Also, the standard cell potential is equal to zero.

Irene Zhou 1E

A change in temperature or concentration would affect the rate constant.

Irene Zhou 1E

An inert electrode is not part of the redox reaction but is needed to conduct the electrons. Use an inert electrode when there are no other solid conducting metals.

Irene Zhou 1E

Cell diagrams only have the cathode and anode substances. The anode are on the left and the cathode is on the right because the cell diagram is meant to follow the flow of electrons.

Irene Zhou 1E

Gib's free energy is the maximum amount of reversible work that can be done. All free energy in this course refers to Gibb's Free Energy.

Irene Zhou 1E

The energy of formation for elements is zero because that is the naturally occurring compound in standard conditions.

Irene Zhou 1E

To find the change in entropy, subtract the molar entropy of the products from the reactants.

Irene Zhou 1E

Change in enthalpy alone does not determine the spontaneity of the reaction. It also depends on the change in entropy and temperature.

Irene Zhou 1E

Solutions of weak acids have a higher pH value than solutions of strong acids because it has a lower concentration of hydronium ions, so it is less acidic.

Irene Zhou 1E

This question is a version of Hess' Law except that the question does not explicitly state each equation. Thus, you need to write out each of the equations and subsequently manipulate them and their respective enthalpy to calculate the overall enthalpy.

Irene Zhou 1E

You would use (3/2)R to calculate the heat capacity, Cvm, of a monoatomic gas when it is at constant volume. You would use (5/2)R to calculate the heat capacity, Cpm, of a gas at constant pressure.

Irene Zhou 1E

We assume gases to be ideal gases for the sake of calculations.
Ideal gases take up no volume and have interactions with other molecules that are insignificant.

Irene Zhou 1E

The heating curve would have a smaller slope because the substance's high heat capacity means that it would be able to absorb more energy for each increase of one degree in temperature.

Irene Zhou 1E

Negative entropy means that the system has become more disordered. Positive entropy means that the system has become more ordered.

Irene Zhou 1E

Bond enthalpies are the averages of many bonds and are calculated under standard conditions. Thus, it can be slightly less accurate than the other methods.

Irene Zhou 1E

Steam at 100 degrees releases a lot more heat and energy than boiling water at 100 degrees so it would be much more painful and harmful

Irene Zhou 1E

I think we will need to know how to solve calculations involving calorimetry.

Irene Zhou 1E

R is a constant so it is always the same. There are different units though so the constant can change based on that. Pay attention to the units given in the problems

Irene Zhou 1E

Apply sig figs to enthalpy as usual.

Irene Zhou 1E

I think it is a good idea to know how to solve calorimetry problems

Irene Zhou 1E

I think we should be getting the test back during discussion so we can study it for the midterm

Irene Zhou 1E

The 5% ionization approximation can be applied to any K calculation as long as K is less that 10^-3

Irene Zhou 1E

I agree with all the previous responses. The smaller the pKa, the larger the Ka, which means the stronger the acid. The same is also true for bases. The smaller the pKb, the larger the Kb, which means the stronger the base.

Irene Zhou 1E

If there are the same number of gas moles on both sides of the equation, then the reaction would not shift to favor either direction.

Irene Zhou 1E

When water is undergoing a change from solid to liquid or liquid to gas, all of the heat supplied during that time is used to break the bonds. Thus, the temperature only increases as the solid, liquid, or vapor continues to heat.

Irene Zhou 1E

When considering sig figs for pH, begin counting the number of significant numbers after the decimal. This is because the pH of 1-14 is not based on error

Irene Zhou 1E

Only aqueous solutions and gases are included in the calculation of the equilibrium constant.

Irene Zhou 1E

Hydrofluoric acid is a weak acid because it does not completely dissociate in water.

Irene Zhou 1E

It usually depends on the units that are given. If the reactants and products are all gases, then Kp can be used. However, it still may be easier to first calculate Kc because the question may provide numbers in terms of moles and liters.

Irene Zhou 1E

Changing the concentration of reactants or products will not change the K value because the change will either result in more reactants or products being formed to bring the reaction back to equilibrium.

Irene Zhou 1E

Always use equilibrium concentrations to calculate K because K is the equilibrium constant.

Irene Zhou 1E

Brackets would denote concentration. Therefore, it would be a better idea to use either parenthesis or nothing at all for partial pressure to minimize confusion.

Irene Zhou 1E

Compare it based on the resulting anion stability. Since Cl is more electronegativity, it will help share the -1 formal charge on the oxygen, resulting in a decreased formal charge and more stable anion. So HOCl is the stronger acid.

Irene Zhou 1E

I think it is a good idea to know everything on his coordination compounds table.

Irene Zhou 1E

Polar bonds are when there is a difference in electronegativity between two atoms sharing a pair of electrons. The more electronegative atom pulls the electrons slightly closer, resulting in polarity.

Irene Zhou 1E

I think we will mostly be calculating the pH from the hydronium ion concentration. The pOH can then be calculated by subtracted the pH from 14. With the pOH, we can solve backwards for the concentration of hydroxide ions.

Irene Zhou 1E

The band of amphoteric oxides is not strictly adhered to the band of metalloids. Water is also an important amphoteric oxide,

Irene Zhou 1E

In the Bronsted definition, an acid is a proton donor and a base is a proton acceptor.

in the Lewis definition, the acid is an electron acceptor and the base is an electron donor.

Just remember that one has to do with protons and the other with electrons.

Irene Zhou 1E

The conjugate seesaw explains the strength of acids and bases in relation to its conjugate acids or bases. A strong acid will translate to a weaker conjugate base. A weak acid will translate to a stronger conjugate base. A strong base will translate to a weaker conjugate acid. A weak base will trans...

Irene Zhou 1E

I do not think we will be asked to calculate pKa because it is merely a way to represent the Ka. We will definitely be asked to calculate pH.

Irene Zhou 1E

The main difference between strong and weak acids or bases is in the degree of dissociation. Strong acids completely ionize, releasing all the hydrogen ions. Weak bases, only partially ionize. It is a good idea to memorize the 7 strong acids and the 7 strong bases.

Irene Zhou 1E

It is probably a good idea to know all of the shapes and how each one comes to be based on the regions of electron density and number of lone pairs. Creating a chart might be helpful with this.

Irene Zhou 1E

If a molecule has a hydrogen that is bonded to N, O, or F and N, O, or F has lone pairs, then that molecule likely has hydrogen bonding

Irene Zhou 1E

Just because a molecule has lone pairs does not mean that it is necessarily polar. It more depends on the where the lone pairs are and how the bonds are placed, if they cancel or not. Think of it as vectors pulling the molecule in opposite directions.

Irene Zhou 1E

The shaded and hatched wedges are just there to help distinguish that the bonds are existing in three dimensions. A shaded wedge indicates that the bond is coming out of the plane while a hatched wedge indicates that the wedge is extending back into the plane.

Irene Zhou 1E

Polarizability corresponds with the interaction between electrons and the nucleus. The less electrons, the stronger the interaction between those electrons and the nucleus. These electrons would be held tightly and have low polarizability because the interaction between those electrons and the nucle...

Irene Zhou 1E

The three lone pairs are in the equatorial plane so the overall shape would be linear.

Irene Zhou 1E

A coordinate bond is formed when one atom provides both electrons for the shared pair with another atom that is lacking such a pair. The two electrons derive from the same atom.

Irene Zhou 1E

A sigma bond is the first bond. Every bond after that is a pi bond. A sigma bond would let the molecule be rotated around the bond.

Irene Zhou 1E

I think drawing it either way would be fine as long as you specify that the molecule is trigonal planar and the bond angle is 120 degrees. Drawing it in its actual position would be a good way to visualize the bond angle though!

Irene Zhou 1E

Usually, we would be asked to find the bond length if there is some sort of resonance. There is no need to memorize any numbers. For example, the question will give the bond length for the single bond. We can determine that the double bond is shorter. If there is resonance and we are given the singl...

Irene Zhou 1E

Hydrogen bonding is the strongest intermolecular force, but it is still weaker than a covalent or ionic bond. Hydrogen bonds are responsible for holding together DNA, proteins, and other macromolecules and the high melting and boiling point of water.

Irene Zhou 1E

The effective nuclear charge increases across the period because of an increase in positive nuclear charge with no accompanying increase in number of electron shells. The effective nuclear charge decreases down a group because the greater size causes a weaker net attraction.

Irene Zhou 1E

I think it is a good idea to know some of the more common polyatomic ions such as ammonia, hydroxide, and sulfate. If it is more complicated, it might be given.

Irene Zhou 1E

I think significant figures will be more important on this test. Pay attention to the question and use the least number of significant figures. One point will probably be docked for each significant figure mistake

Irene Zhou 1E

A Lewis acid accepts a pair of electrons while a Lewis base donates a pair of electrons

Irene Zhou 1E

It may be a good idea to know a few of the basic ones, such as sulfate and ammonium. Otherwise, I think they will be provided or stick to the common ones.

Irene Zhou 1E

The midterm will cover the high school review of chemistry from the first test and the Quantum Chemistry that we are learning now and whatever we cover before the midterm.

Irene Zhou 1E

They can exist in different orbitals. Two electrons cannot have the same exact four quantum numbers. The fourth number dictates the spin of the electron.

Irene Zhou 1E

Electron affinity is the energy that is released when an electron is added to an atom. Electronegativity is the atom's tendency to attract an electron in a shared bond. The two terms are similar, but different.

Irene Zhou 1E

The cone itself is a nodal plane because the probability of locating an electron in that plane is zero.

Irene Zhou 1E

The different axes are referring to the nodal planes of the different electron orbitals. The nodal planes are where there is zero probability of finding an electron.

Irene Zhou 1E

Since we won't be doing actual calculations with Schrodinger's Wave Function Equation, I think we just need to understand how it describes quantum mechanical behavior.

Irene Zhou 1E

The electrons will descend one energy level at a time since it is quantized. Thus, the energy levels are discrete and not continuous

Irene Zhou 1E

The empirical formula and the molecular formula can be the same! It just means that the molecular formula is already in the simplest form. This can be verified if the mass of the empirical formula is the same as the molar mass of the compound.

Irene Zhou 1E

Basically, a metal's threshold energy is the minimum amount of energy that is needed an electron to be ejected from the metal. Each photon needs to have this energy in order for an electron to be ejected.

Irene Zhou 1E

400.00 and 400.0 do not have the same number of sig figs because 400.00 if more accurate to a hundredth place than 400.0

Irene Zhou 1E

125 and 125. have the same number of sig figs! Sometimes it may be confusing if the numbers end in 0. For example 120 and 120.0 have different sig figs because of the decimal in place.

Irene Zhou 1E

Yes, ml always has to be converted to liters because the units of molarity is moles/liter. If the units are not in L, the units will not cancel appropriately

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