CHEMISTRY COMMUNITY

Anastasia Yulo 1C

Heat capacity is the ratio of the amount of heat energy transferred to an object to the resulting increase in its temperature. (J/K) Specific heat capacity is a measure of the amount of heat necessary to raise the temperature of one gram of a pure substance by one degree K. (J/gK) Specific heat capa...

Anastasia Yulo 1C

The closest one can get to an isolated system would be to use something like a bomb calorimeter. However, even a bomb calorimeter is not perfect adn there would inevitably be an escape of energy.

Anastasia Yulo 1C

To help decide which R to use, I am always wary of the units at play. For PV=nRT it would make the most sense to use R = 0.08206 L.atm.K^-1.mol^-1

Anastasia Yulo 1C

For a system in a calorimeter, you would use q=mc delta T
where c is specific heat (K/Kg K)

Anastasia Yulo 1C

For this question, change in internal energy is not equal to 0 because there is a change in volume. A change in volume indicated that work is being done and thus there must be a change in internal energy since U=q+w

Anastasia Yulo 1C

Yes, U=q if volume is constant because there is no work being done (w=0)

Anastasia Yulo 1C

When percent dissociation is less than 5%, then typically x is considered negligible.

Anastasia Yulo 1C

Mastering the questions given on the outlines regarding le Chatlier's principle would best prepare for the midterm according to the website information :-)

Anastasia Yulo 1C

Yes, for endothermic reactions, the k value increases when temperature increases. This website explains how temperature changes affect k: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Equilibria/Le_C...

Anastasia Yulo 1C

Argon is an inert gas and does not react with the elements, therefore it does not affect the reaction.

Anastasia Yulo 1C

keeping track of the given units of the problem helps to determine with gas constant to use!

Anastasia Yulo 1C

We cannot always use specific heat capacity because the mass is not always given in problems. It depends on the context of the problem!

Anastasia Yulo 1C

Calibrating a calorimeter means obtaining the heat capcity of the calorimeter so that it can be used for experiments!

Anastasia Yulo 1C

Changes can be made to an isolated system. What makes this system characteristics is that it's matter and energy is not exchanged with its surroundings.

Anastasia Yulo 1C

A bomb calorimeter is considered an isolated system. This is because matter nor energy is being exchanged with the surroundings outside of the bomb calorimeter.

Anastasia Yulo 1C

For a particular redox reaction, BrO− is oxidized to BrO−3 and Fe3+ is reduced to Fe2+. Complete and balance the equation for this reaction in basic solution. The phases are optional. Answer: BrO−+4OH−+4Fe3+ ⟶ BrO−3 + 4Fe2+ +2 H2O To solve for this, I added H2O and OH to balance out the oxygens. Whe...

Anastasia Yulo 1C

For this question the inequalities are at the bottom of the graph, and the spontaneity is at the top of the graph!

Anastasia Yulo 1C

T is the temperature of the reaction! Typically this is given. Also, remember that in Gibbs free energy, that temperature is in kelvins and not celsius!

Anastasia Yulo 1C

Great question! There are no units, because they all cancel out. If you were to make a fraction of products over reactants with the respective units (molarity)...you would find that they all cancel! This is because K is a ratio of products and reactions at equilibrium.

Anastasia Yulo 1C

To solve this problem, it was useful for me to remember the conceptuals behind entropy (S) and enthalpy (H). Entropy is the measure of "disorder", thus when going from liquid to gas...there is more disorder and thus an increase in entropy. To break the bonds to go from liquid to gas, energ...

Anastasia Yulo 1C

Entropy is always positive when looking at the entropy of the universe, as entropy and disorder is always increasing when looking at the system perspective of the universe.

Anastasia Yulo 1C

What helps in determining which R constant to use, is to be wary of the units that are being used!

Anastasia Yulo 1C

What helps me solve this problem is to remember the conceptuals behind entropy and enthalpy. Entropy is the measure of "disorder", thus when going from liquid to gas...there is more disorder and thus an increase in entropy. To break the bonds to go from liquid to gas, energy is required an...

Anastasia Yulo 1C

A piston confines 0.200mol Ne(g) in 1.20L at 25 degrees Celsius. Two experiments are performed: a.) The gas is allowed to expand through an additional 1.20L against a constant pressure of 1.00 atm b.) The gas is allowed to expand reversibly and isothermally to the same final volume which process doe...

Anastasia Yulo 1C

NO2 is non-linear, so you would use the molar heat capacity for that (3R). Therefore c (molar heat capacity) = 3R, Where R is the last constant. for the first part of the question you would use q = mc delta t The m would be in moles since c is molar heat capacity. The moles are given, and using the ...

Anastasia Yulo 1C

NO2 is non-linear, so you would use the molar heat capacity for that (3R). Therefore c (molar heat capacity) = 3R, Where R is the last constant. for the first part of the question you would use q = mc delta t The m would be in moles since c is molar heat capacity. The moles are given, and using the ...

Anastasia Yulo 1C

To find the volume change you would use PV = nRT. However, it is significant to recognize that n = to moles of N2 (g) and not Na(s) or NaN3. You can find the moles of N2 via stoichiometry given the moles of NaN3.

Anastasia Yulo 1C

For reversible reactions, w = -nRT x ln(Vf/Vi) whereas w=-delta n x R x T for irreversible reactions.

Anastasia Yulo 1C

What is important is to recognize that the sum of the neutralization volumes is equal to the given information regarding the specific heat capacity. In your case it gives information on the specific heat capacity for 0.600 L. The next information is given 0.300 L HClO2 + 0.300 L NaOH = 0.600L This j...

Anastasia Yulo 1C

For path A, we need to know the number of moles (n). We find this by using PV=nRT Where P is given (2.54 atm), V is given (3.98L), T is given (298K) and R is the constant 0.0821 Latm/Kmol After solving for n, you would plug it into w=-nRT x ln(Vf/Vi) We use this specific equation because it is a rev...

Anastasia Yulo 1C

Work is not a state function because a state function is a property whose value does not depend on the path taken to reach that specific value. Work depends on the path taken.

Anastasia Yulo 1C

I would look at the units for the problem involved! For example, if it is specific heat then you would know that Kelvin is necessary since specific heat includes kelvins.

Anastasia Yulo 1C

Because inert gases are non-reactive, the partial pressures do not change when an inert gas is added to a system.

Anastasia Yulo 1C

Molar heat capacity is the amount of Energy necessary to change 1 mole of the substance by 1 Kelvin. If the given is only in moles, you can use either specific heat capacity by calculating the mass or by directly using moles given.

Anastasia Yulo 1C

Specific heat capacity is defined as the amount of heat required to raise the temperature of 1 kilogram of a substance by 1 kelvin (SI unit of specific heat capacity J kg−1 K−1). This is an intensive property because it is a property of matter that does not change as the amount of matter changes.

Anastasia Yulo 1C

Hello! Typically when K is lower than 10^-5, then it is a good gauge on whether or not to approximate. When the percent of ionization is less than 5%, then approximation of x can definitely be used. x is so small that its decrease from the original reactant concentration is negligible. However, the ...

Anastasia Yulo 1C

x is so small that its decrease from the original reactant concentration is negligible. However, the final concentrations are significant to the K value that they cannot be neglected regardless of how small x is.

Anastasia Yulo 1C

It helps to remember these formulas:
-log(Ka)=pKa, -log(Kb)= pKb

pKa + pKb = 14
Ka x Kb =10^-14

and pH+pOH=14

Anastasia Yulo 1C

I would memorize the strong acids and bases chart. There is also a chart of common weak acids and bases. That helps me determine if a salt is acidic or basic. However, as the precious answers explained it helps to remember this rule of thumb: if Ka > Kb, the ion is acidic; if Kb > Ka, the ion is bas...

Anastasia Yulo 1C

Hello! I tend to solve for the quadratic by finding the 0 on the graph. However, there was a time during sample where my answer for x was negative despite how many times I checked my work. However, once I used the quadratic formula I was able to solve for a positive x. Mathematically, I can't explai...

Anastasia Yulo 1C

It helps me to understand Le Chatelier's principle as a way to maintain balance and equilibrium of a reaction. If there are too many products, then the reaction will produce more reactants. The reaction will shift from products and/or reactants depending on the changes that it experiences.

Anastasia Yulo 1C

I understand that volume is the only change which has an effect on concentration and thus is the only change in pressure which has an effect in the direction of the reaction. However, wouldn't the addition of an insert gas change the individual partial pressure of products and reactants? And as a re...

Anastasia Yulo 1C

Pure solids or liquids are excluded from the equilibrium expression because their effective concentrations stay constant throughout the reaction. The concentration of a pure liquid or solid equals its density divided by its molar mass.

Anastasia Yulo 1C

In the same way that a high pKa indicates a strong acid, the same goes for a high pKb and strong bases. A large pK indicated that products are high. Therefore, when bases are highly disassociated (strong base) there is a large product concentration.

Anastasia Yulo 1C

Hey! The ICE box is only used for weak acids and bases.This is because they don't fully dissociate in water.
Strong acids and bases, on the other hand, completely ionize. Thus, we can just use the pH, Ka, or Kb formula. With strong acids and bases an ICE box is not necessary given their behavior.

Anastasia Yulo 1C

Products and reactants are typically given. Sometimes when the initial of products is given, an ICE table can be used to find the final concentration of products and reactants and equilibrium.

Anastasia Yulo 1C

Kc is the equilibrium quotient which takes into account concentration. Kp is the equilibrium quotient which takes into account pressure. Given partial pressures, concentration can be solved using PV=nRT.

Anastasia Yulo 1C

Solids and liquids have little change to no in heterogenous reactions, so we just do not take them into account when calculating K because of their small participation in equilibrium

Anastasia Yulo 1C

Q is the reaction quotient. That is, the concentration of the products over the reactants. K is a reaction quotient where the values are at equilibrium. Q is subject to change for a reaction as the amounts of products and reactants can change. However, Q will eventually = K, as reactions eventually ...

Anastasia Yulo 1C

If the given information is kp, then the rice table would use partial pressure. If the given information is kc, then molarity/concentration would be used.

Anastasia Yulo 1C

Although this topic is not covered in the exams, I was just trying to understand conceptually how extreme pH denatures enzymes. I understand the critical importance of pH in biological systems, but what is taking place from a chemistry standpoint when an enzyme is in an extremely acidic or extremely...

Anastasia Yulo 1C

Dipole arrows show where the electrons have a high propensity to lie. They typically point to the most electronegative atom in the molecule. For example, in H2O the dipole arrows would point toward the oxygen atom.

Anastasia Yulo 1C

Table J.1 on page F77 in the textbook provides a table for commons strong acids and bases. I found memorizing these were extremely helpful! However, remembering that large bond lengths and highly EN anions also make strong acids is also helpful to remember conceptually.

Anastasia Yulo 1C

At least biologically speaking, pH really matters for various systems. For example, we NEED strong acids in our digestive system to break down food, otherwise we'd not be able to extract nutrients as efficiently. However, enzymes denature in acids, therefore our bodies produce the sodium bicarbonat...

Anastasia Yulo 1C

At least biologically speaking, pH really matters for various systems. For example, we NEED strong acids in our digestive system to break down food, otherwise we'd not be able to extract nutrients as efficiently. However, enzymes denature in acids, therefore our bodies produce the sodium bicarbonat...

Anastasia Yulo 1C

Yes, you're completely correct in that size contributes a lot to how strong a bond is. Larger radii means larger distance between nuclei, which creates a bond that is easier to break. Also, bond order is extremely important in determining bond strength. Triple bonds are a lot stronger than double b...

Anastasia Yulo 1C

The ions Na+ and Cl− are spectator ions and don't react with water. So, the pH doesn't change. A spectator ion is an ion that exists as a reactant and a product in a chemical equation.

Anastasia Yulo 1C

All Bronsted-Lowry acids are Lewis acids, but the reverse is not true. Every Bronsted-Lowry base is also a Lewis base, but the reverse is not true.
A Lewis acid is anything that accepts a pair of electrons, while a Bronsted acid accepts pairs of electrons at an acidic hydrogen

Anastasia Yulo 1C

I understand how to solve for pH. But I am having a hard time conceptualizing the significance of the presence of protons (H+) in solutions? Why is knowledge of pH important and what makes a highly acidic/basic solution special?

Anastasia Yulo 1C

NH4Cl is a salt. When it dissolves, the NH4+ ions in water can donate a proton. This ability to donate protons lowers the pH.

Anastasia Yulo 1C

The carbon usually forms 4 bonds because it wants to fill up it's 4 orbitals (2sp3) to be stable. There are many reasons why carbon can be called "special" - it can form huge chains of carbon that can form macromolecules which are big enough for larger organism to use. - it is very stable...

Anastasia Yulo 1C

Becase H2O has 2 lone pairs, it has a AX2E generic formula. This is a bent shape. Remember that A is the central Atom, X is the # of bonded atoms, and E is the # of lone pairs This chart is very helpful in recognizing the shapes: https://www.templateroller.com/template/86292/vsepr-theory-molecular-s...

Anastasia Yulo 1C

I studies the shapes that he shared on lecture and tried my best to understand them conceptually so that I could understand them:Trigonal Planar, tetrahedral, trigonal bipyramidal, octahedral, trigonal pyramidal, see-saw, square planar. Once I recognized the pattern in the repulsions, it helped me m...

Anastasia Yulo 1C

In neutral state, Bromine is smaller than Na due to it's location on the far right of the periodic table. However, Br- is an anion. Anions have bigger ionic radii than their corresponding neutral atoms.

Anastasia Yulo 1C

Correct, photons do not have mass but they still have a momentum which allows it to carry Energy. An object can have momentum without mas if it is a wave. A wave transports momentum via its waving motion and not by physically transporting an object with mass.

Anastasia Yulo 1C

If Carbon only has 2 unpaired electrons, why does it form 4 bonds?
How does this ability to form 4 bonds make organic molecules so special?

Anastasia Yulo 1C

Ionization energy and electronegativity decrease down a group. Ionization energy and electronegativity also increase across a period. What helps me remember this is to remember that fluorine is the smallest and most electronegative atom, if you look at the periodic table you will see that it is at t...

Anastasia Yulo 1C

In determining bond strength, which characteristic take priority? Is it size of atom (and thus bond length) or electronegativity of an atom in a molecule? CF4 has a very strong bond because of the small size of the fluorine atom and the short bond lengths. The textbook also says, "note that ele...

Anastasia Yulo 1C

To elaborate on the statement "note that electronegativity and polarity arguments would predict the C--F bond to be the weakest", because Fluorine is highly electronegative, then the bond is weak because F is strongly attracting the electron which belong to Carbon. Thus it would be easier ...

Anastasia Yulo 1C

The formal charge of an atom indicates the gain or loss of an electron while forming a covalent bond. To determine the formal charge I use the following rationale: Formal Charge = Valence electrons of neutral atom - (Shared electrons/2 - lone pair electrons)

Anastasia Yulo 1C

When looking at the lewis structure, polarity can be determined from the symmetry of the lewis structure. The more symmetrical the appearance of the lewis structure is, the more likely it is to be polar. Also, knowing the electronegativity of each element (from the trends) is a consistent reliable w...

Anastasia Yulo 1C

The formal charge is the charge that an atom appears to have when we count the electrons according to certain arbitrary rules. Formal charge is an integer property that is essential for the correct valence representation of a molecule.

The partial charge is the charge that the atom really has.

Anastasia Yulo 1C

I remember that helium is the smallest atom and that francium is the largest. Because there are added shells with each descending row, I know that as I go down, atoms get larger. Also, I know that noble gases are the most stable elements and thus they are more tightly held..thus I remember that as I...

Anastasia Yulo 1C

Electronegativity determines the intramolecular forces (the forces that hold atoms in place). Electronegativity will determine whether the molecule is polar or non-polar, in other words, the chemical bond. The intramolecular forces affect the nature of the INTERmolecular forces (forces that hold mol...

Anastasia Yulo 1C

The difference in electronegativity needs to be between 0.5 and 1.6 to be considered polar!

Anastasia Yulo 1C

Sum of oxidation numbers for a neutral compound is always 0. Sum of oxidation numbers for a polyatomic ion is the ion charge. When calculating oxidation numbers, remember that group 1A elements are always +1, Group 2A are always +2, Halogens are usually -1 (positive with oxygen). Hydrogen is always ...

Anastasia Yulo 1C

When the energy is higher, the wavelength is shorter. This relationship can be observed from the energy equation. n=6 to n=1 has a greater energy emission than n=6 to n=5, therefore the wavelength would be shorter.

Anastasia Yulo 1C

All electrons behave wave-like and particle-like. Larger objects are not affected by waves because they are so massive, and they are also more predictable than small objects. These principles are derived from the Heisenberg Uncertainty Principle.

Anastasia Yulo 1C

The intensity of light is dependent on the amount of photons. However the intensity does not determine on the overall energy.
The photoelectric effect shows that frquency has effect on the ejection of electrons.

Anastasia Yulo 1C

I conceptualize it using this equation: https://www.google.com/imgres?imgurl=https%3A%2F%2Fslideplayer.com%2Fslide%2F3866354%2F13%2Fimages%2F8%2FThe%2Bphotoelectric%2Bequation.jpg&imgrefurl=https%3A%2F%2Fslideplayer.com%2Fslide%2F3866354%2F&tbnid=YQrn8DIi441WVM&vet=12ahUKEwijxoaQ4fPsAhVh...

Anastasia Yulo 1C

Technically, electrons have an angular momentul which is a type of momentum possessed by rotating objects. This attributes the spinning nature and it is is a fundamental characteristic of electrons.

Anastasia Yulo 1C

Bond length is defined as the distance between the centers of two covalently bonded atoms. The length of the bond is determined by the number of bonded electrons (the bond order). The higher the bond order, the stronger the pull between the two atoms and the shorter the bond length.

Anastasia Yulo 1C

Fluorine is the most electronegative element because it has 5 electrons in it's 2P shell. Because it only requires 1 electron to reach stability, it is highly reactive.

Anastasia Yulo 1C

Those elements are just exceptions to the octet rule.

Anastasia Yulo 1C

Electronegativity is the ability of an atom to attract electrons from outside, it is a qualitative property, measured from Pauling units, and it's applied for a single atom. Electron affinity is the amount of energy released when a neutral atom or molecule gains an electron from outside, it is a qua...

Anastasia Yulo 1C

It depends on which equation is being used.

R = 3.28984 x10^15 Hz is used for the Rydberg equation with frequency, or v = R(1/n1^2 - 1/n2^2).
R = 1.097x10^7 m is used for the Rydberg equation with wavelength, or 1/wavelength = R(1/n1^2 - 1/n2^2).

Anastasia Yulo 1C

The equation is actually E=hc/λ where λ is wavelength.
However we can extract the equation c/λ = v where v is frequency and c is the speed of light.

Anastasia Yulo 1C

The particle model is used for atomic spectroscopy

Anastasia Yulo 1C

The fundamentals until 1D. These topics are on the chemistry website.

Anastasia Yulo 1C

In this class, you can always count on c being the speed of light.

Anastasia Yulo 1C

Typically nu denotes frequency, which looks like an italicized v. A diligent way to confirm whether or not it is velocity or frequency is to check the units! Velocity is in m/s whereas frequency is in Hz. Typically the speed of light is denoted with "c"

Anastasia Yulo 1C

This infograpgic was helpul to me when differentiating the terms: https://pediaa.com/wp-content/uploads/2 ... ummary.png

Anastasia Yulo 1C

4s orbitals are said to have a lower energy than the 3d orbitals because they are filled first.

Anastasia Yulo 1C

Shells are composed of electrons that share the same principal quantum number. Whereas subshells are composed of electrons that share the same angular momentum quantum number whereas orbitals are composed of electrons that are in the same energy level but have different spins. This infographic helps...

Anastasia Yulo 1C

Thanks so much for your advice! I will definitely keep my notes handy as I go through my UCLA journey. Can you tell us a little bit more about your gap year? What types of clubs/ internships/ research opportunities/ etc. you were involved in that helped strengthen your medical school application? M...

Anastasia Yulo 1C

Thank you so much for dedicating time to writing this. It was so incredibly helpful to me.

Anastasia Yulo 1C

100g is a tool to help conceptualize the elemental proportions of a molecule to equal 100%. It's an arbitrary number that always works in those problems.

Anastasia Yulo 1C

Why do chemists like nitrates so much?
They're cheaper than day rates.

I asked the guy sitting next to me if he had any Sodium Hypobromite…
He said NaBrO

Anastasia Yulo 1C

I allocate a set time to review my notes and perhaps for practice problems, but not too much time at once. If I overspend my time all at once for studying I am overwhelmed. So, maybe 30 min of skimming over my notes, and then 20 minutes doing some problems. That is one session. Then, I take breaks t...

Anastasia Yulo 1C

When completing problems on solutions, I am not quick to apply the formulas in which you described (M=n/v or M Initial V final = M final V final) When it comes to solutions concentrations, it helps to internalize and conceptualize the principles used to create those formulas. When diluting a solutio...

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