CHEMISTRY COMMUNITY

stephaniekim2K

During expansion, work is being done so you need a negative sign while compression you need a positive sign.

stephaniekim2K

No, because you can't have a negative value for the amount of energy required to raise the temperature.

stephaniekim2K

A calorimeter measure the heat change when a reaction occurs. A bomb calorimeter, though, has constant volume.

stephaniekim2K

A bomb calorimeter is constant volume.

stephaniekim2K

A calorimeter measures the change in temperature, but a bomb calorimeter has constant volume.

stephaniekim2K

Energy cannot leave in a closed system, so only temperature or pressure can change.

stephaniekim2K

Unless stated, just assume that it is at constant pressure.

stephaniekim2K

Enthalpy is the heat absorbed/released while internal energy is just the total amount of energy.

stephaniekim2K

A bomb calorimeter is more resistant to pressure.

stephaniekim2K

Delta H is based on the amount of substance used while Q is the amount of energy released in total.

stephaniekim2K

In a closed system, energy cannot be transferred to the outside.

stephaniekim2K

Steam has more energy than liquid because more energy is required to transform a liquid into steam. For this reason, as steam touches the skin, much more energy is transferred, causing burns.

stephaniekim2K

Yes, although I believe strong acids and bases have K values, they are so excessively big.

stephaniekim2K

If a reaction is endothermic, heat is required so adding heat to is would favor the reactants.

stephaniekim2K

In an exothermic reaction, heat is produced, so there is heat in the products. Adding heat to the reaction would favor the reactants.

stephaniekim2K

There's a few different gas constants for different units but they are the same constant, just with different units. They are all on the formula sheet.

stephaniekim2K

pH is equal to the -log^[H3o+] so the lower the concentration of [H3O], the smaller the pH, meaning it is a strong acid. Since the pH of H2O is 7, neutral, [H3O]=10⁷.

stephaniekim2K

If the acid or base isn't dissociated completely, it is weak. Otherwise, a very low or a very high pH (or a very high or a very low pOH) means it is a strong acid or base.

stephaniekim2K

Removing H₂ would make the reaction shift toward the reactants because of Le Chatlier's, so more N₂ would be produced.

stephaniekim2K

[H30+]=-log^pH and [OH-]=-log^pOH.

stephaniekim2K

Kc is the equilibrium constant that's calculated by the concentrations but it is calculated the same way as just "K."

stephaniekim2K

Since Ka is smaller than 10³ you can ignore the x in the denominator. Since K is so small, x is negligible in this case and can be ignored for the sake of convenience of calculating.

stephaniekim2K

p just means its the log of something. so pKa is log(Ka) and pKb is log(Kb).

stephaniekim2K

Temperature affects the equilibrium constant so if the reaction is exothermic (heat in the products) added heat will shift the reaction left and removing heat will shift the reaction right. On the other hand, if the reaction is endothermic (heat in reactants) added heat will shift the reaction right...

stephaniekim2K

The number of sig figs to the answer of a log is the amount of sig figs after the decimal of the number you took the log of.

stephaniekim2K

You include any gases, but since solids and liquids have negligible change they are not included in ice box or the equilibrium constant.

stephaniekim2K

Weak acids and bases are reversible because they don't dissociate completely, but strong acids and bases on the other hand dissociate completely so they are not reversible.

stephaniekim2K

No he only draws the structures for clarity but they are only for 14a not 14b.

stephaniekim2K

K_c is solved using concentration while K_p is solved using partial pressures.

stephaniekim2K

Q is solved the same way as K, Q is just not at equilibrium.

stephaniekim2K

P=pressure
V=volume
N=moles
R= ideal gas constant
T=temperature

stephaniekim2K

K is the constant at equilibrium while Q is the constant at any point in the reaction.

stephaniekim2K

When the gas and liquid states are at equilibrium, the pressure of the gas is known as the vapor pressure.

stephaniekim2K

Partial pressure is used in this case because they are gases.

stephaniekim2K

Homogeneous equations are all in the same state of matter, while heterogeneous are in mixed states of matter.

stephaniekim2K

Seeing as the formula for K is K = [P]/[R], the larger the concentration of products and the smaller the concentration of reactants there are, the larger K will be.

stephaniekim2K

Solids and liquids have constant concentrations so they don't change, so there is no need to calculate them.

stephaniekim2K

According to the constant formula (K = [P]/[R]) the value of K will be higher, meaning there is more product than reactant left at the end. This being said, a more stable molecule results in more product and less reverse reaction happening.

stephaniekim2K

A ligand is a chelate when it bonds in more than one area.

stephaniekim2K

You use these suffixes when there is already a suffix in the name.

stephaniekim2K

You will have to memorize the polyatomic ions, but I'm pretty sure he won't give anything that's too difficult.

stephaniekim2K

If the charge is negative you add -ate.

stephaniekim2K

The transition metal and its ligands go inside the bracket. Everything else is outside.

stephaniekim2K

They are structure with the same formal charges.

stephaniekim2K

Yes they are all the same.

stephaniekim2K

No, because it is the same structure it has the same name.

stephaniekim2K

Resonance structures are different ways a lewis structure can be drawn, but they have the same formal charge.

stephaniekim2K

Lone pairs position themselves in a way where there is minimal repulsion.

stephaniekim2K

You need to draw the lewis structure and it helps to draw arrows to the negative charged atom from the positively charged ion. If there are two different poles, then the molecule is polar, if both cancel out, it is nonpolar.

stephaniekim2K

Chlorine cannot have more than a single bond so we know that there are 3 single bonds on iodine, meaning there will be two left over lone pairs on iodine.

stephaniekim2K

You need both to figure out if it is polar/nonpolar. Electronegativity will tell where the pull of electrons is, but the Lewis structure shows the positioning of the atoms and whether they will cancel or not.

stephaniekim2K

There is a greater difference in electronegativity.

stephaniekim2K

Ionic character, I believe, is a covalently bond that has such strong ionic character (electronegativity) that a covalently bonded substance is almost ionic.

stephaniekim2K

An ionic bond is typically comprised of a non metal and a metal while a covalent bond is usually two non metals.

stephaniekim2K

Just know the general trend on the periodic table.

stephaniekim2K

Both ionization energy and electronegativity increase toward the upper right hand side of the periodic table.

stephaniekim2K

Electron affinity is the energy released when an electron in added to to an atom, while electronegativity is how much an atom pulls electrons.

stephaniekim2K

Hydrogen, helium, and boron are all exceptions to the rule.

stephaniekim2K

Lone pair electrons are electrons that are not bonded to other elements. In other words, they are not shared with any other elements.

stephaniekim2K

Elements P, Cl, and S do not adhere to the octet rule because of the d orbital.

stephaniekim2K

Typically, the element with the lowest ionization energy will go in the center.

stephaniekim2K

Sulfur, Phosphorous, and Chlorine all deviate from the octet rule because they have the extra d orbitals.

stephaniekim2K

If the question asks for Lewis structures, I assume it is just the 2D model without angles. I'm sure if we learn about bond angles there will be a separate question.

stephaniekim2K

Typically, if not mentioned, you use the speed of light in a vacuum.

stephaniekim2K

Sometimes you are given some info but not others, so in order to solve with the info given you can rearrange them to fit the info you have.

stephaniekim2K

For tests at least, I used the constant given on the front sheet and I got full points for the problem.

stephaniekim2K

I find it easier to convert when you first convert to meters, then to the needed measurement from there.

stephaniekim2K

The unit is 1/s which is essentially s^-1

stephaniekim2K

1 Angstrom is equal to 10^-10 meters

stephaniekim2K

3.00 x 10^8 is the speed of light inside a vacuum.

stephaniekim2K

The unit is simply second^-1 or 1/s.

stephaniekim2K

Based on the equation for the speed of light, c = λ ν, c is a constant, so λ and ν are inversely proportional because they are being multiplied. As one goes up, the other value must go down, and vice versa. For example, if λ, the wavelength goes up in value, the frequency, ν, must respond accordingl...

stephaniekim2K

Since C=λν, frequency and wavelength are inversely proportional, meaning that as one increases, the other decreases since the speed of light, c, is constant. By decreasing the wavelength, you can increase the frequency.

stephaniekim2K

400nm (1m / 10^9nm) (1 A / 10^-10m) = 4000 A

stephaniekim2K

Personally, I have a calculator that keeps track of all the problems I did previously (TI-84), so what I do is when I am doing work on paper, I will write the answer (throughout the problem not the final answer) with the amount of sig figs that are called for, but when I am calculating the next port...

stephaniekim2K

It might also help to examine the full equation and start with the elemnts or molecules taht appear the least amount of times on each side and work your way up. I agree that this is one of the easiest ways for me to balance equations. Professor Lavelle did also mention this method as his way of bal...

stephaniekim2K

Atoms cannot be created or destroyed according to the Law of Conservation in chemical reactions, but Professor Lavelle did mention that in the future we will learn about a different type of reaction where atoms can be created of destroyed.

stephaniekim2K

Like most people said already, the order is not very important, but there is a method called the Hill System that states that Carbon atoms are listed first, then Hydrogen, and the rest of the atoms alphabetically.

stephaniekim2K

Theoretical yield is the calculated amount of yield you get when you plug in values into an equation. Percent yield, however, is the percentage of how much actual yield is produced out of the theoretical yield. Factors that inhibit reactions from producing 100% yield occur because of loss of product...

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