CHEMISTRY COMMUNITY

Sofia Barker 2C

If you plot [A] vs time and get a straight line, this tells us that the reaction is zero order.
If you plot ln [A] vs time and get a straight line, this tells us that the reaction is first order.
If you plot 1/[A] vs time and get a straight line, this tells us that the reaction is second-order.

Sofia Barker 2C

The units of k are L/(mol x seconds) for a second-order reaction.
You can solve for the units through the equation rate = k[concentration]^2.
k = rate / [concentration]^2
k = mol/(L x seconds) / (mol/L)^2
k = (mol / Ls) x (L^2 / mol^2)
k = L / mol S, which can be written as 1/(M x s), M being molarity

Sofia Barker 2C

Yes, you would find the value of -k, the slope, through rise over run. The absolute value of the slope is equal to k.

Sofia Barker 2C

how would we determine if it is a positive or negative slope? Or do we just have to memorize it ? If given a set of [A] values vs time, you can determine the slope by taking the inverse of each [A] value, which gives the 1/[A] value, and see if it increases or decreases over time. That way you can ...

Sofia Barker 2C

Intermediates are used up in a reaction, while catalysts are not. However, neither show up in the overall reaction for a chemical reaction because they are found on both the product and reactant side of different steps of a reaction and thus cancel out. Catalysts appear as reactants in one step and ...

Sofia Barker 2C

Zero order reactions are reactions in which the rate of the reaction only depends on the rate constant, not the concentration of reactant. The book gives an example, which is the reaction 2 NH3(g) --> N2(g) + 3 H2(g). Experiments show that no matter the initial concentration of NH3, the reaction alw...

Sofia Barker 2C

Zero-order reactions, unlike first and second-order reactions, are independent of the concentration of reactant and only dependent upon the rate constant, k.

Sofia Barker 2C

The slow step of a reaction is always the rate-determining step for an overall reaction.

Sofia Barker 2C

In the Arrhenius equation, A is a constant that varies for different reactions. It is called the frequency factor or pre-exponential factor and it is simply a value that takes into account the frequency of collisions when determining the rate constant for a specific reaction.

Sofia Barker 2C

Rate-limiting or rate-determining steps of a reaction are the slowest steps of the reaction because they determine the rate of the entire reaction. I believe that questions will identify which reaction is slow and which are fast.

Sofia Barker 2C

for any reaction aA --> bB + cC, the rate based on the concentration of reactants is negative (-1/a * d[A]/dt) because the concentration of reactants decreases over time as products are formed. In the reverse reaction, A becomes a product and thus its rate is positive because its concentration incre...

Sofia Barker 2C

The units for rate are M/s, or mol/Ls, because rate is change in concentration over time.

Sofia Barker 2C

In his example during class, he divides (2.7*10^-7 mol/Ls = k(0.1M)^n (0.01M)^m) by (1.35*10^-7 mol/Ls = k(0.1M)^n (0.005M)^m). This gives an overall equation of 2 mol/Ls = 2^m, since the two k(0.1M)^n terms cancel out. He isn't setting rate 1/ rate 2 equal to a specific value, he is simply dividing...

Sofia Barker 2C

Based on how we used the equations we derived in class before the midterm, I believe that we simply just need to know the equations themselves and not how to derive them.

Sofia Barker 2C

Thermodynamic analyses indicate the stability of a reaction and its components in different states, while kinetics looks into the rate of reaction and what factors influence it.

Sofia Barker 2C

Galvanic cells create electrical energy from chemical energy. This reaction is a spontaneous redox reaction.
Electrolytic cells create a potential difference from electrical energy. The electrons are forced to flow, creating a nonspontaneous redox rxn.

Sofia Barker 2C

Charge builds up as electrons move from the anode (-) to the cathode (+). It is important to neutralize the charge build-up so that electrons can continue to flow. Without a salt bridge, the electrons would stop flowing to the cathode because the build-up of negative charge would repel them. The sal...

Sofia Barker 2C

Ampere is a measure of current, which is essentially the amount of charge passing over a certain period of time (C/s). Coulombs is simply a unit to quantify the amount of charge.

Sofia Barker 2C

Add H2O to the side with less O and then add H+ to balance out the H+ on the other side of the reaction. The general rule is to add H2O to balance out O and to add H+ to balance out the H+ on either side of a reaction. If a solution is basic, add OH- to get rid of H+ If a solution is acidic, add H+ ...

Sofia Barker 2C

For 5G 13 and 5G 15, the textbook solutions manual keeps the product and reactant partial pressures in units of bar to calculate Q. Why isn't it necessary to convert to atmospheres? I calculated Q using bar and then again using atm and the values are different, so the reasoning can't be that they ar...

Sofia Barker 2C

Delta U can be zero despite expansion because delta U represents a change in energy, so for there to be no change in energy, the energy gained / lost due to work would be made up for in a gain or loss of heat.

Sofia Barker 2C

K values change with temperature, so the k value for one temperature will be different compared to a k value at another temperature. While pressure, volume, and concentration changes only shift the equilibrium of a reaction, temperature changes the actual k equilibrium value.

Sofia Barker 2C

C(s) is irrelevant because it is in solid form. The concentrations of solids do not change throughout a reaction, which is why solids are considered pure substances.

Sofia Barker 2C

I believe it is theoretical because no biological or chemical process is 100% energy efficient. Energy transfers are not perfect, so there will always be at least a small amount of it that becomes heat instead of 'useful' energy that can be used to do work.

Sofia Barker 2C

Delta G is positive when K is less than one because the ln of a fraction is a negative number. Since there is a negative sign in the equation delta G = -RT ln K, the two negatives cancel and the overall value is positive.

Sofia Barker 2C

If you have a value with units L atm, use the gas constant R = 8.206 x 10^-2 L atm / mol K. You can also convert Latm to joules by using the conversion 101.325 joules per L atm. This allows you to use the other gas constant, R = 8.314 joules / mol K.

Sofia Barker 2C

The ice is absorbing the heat given off by the water. We know that exothermic reactions have a positive delta H because they are taking in heat, whereas endothermic reactions have a negative delta H value because they release heat. We can use this same logic with this problem to conclude that the q ...

Sofia Barker 2C

You should use the equations delta U = q+w and w = -P(delta V). q is given as 5.50 kj, but w is not given. Since the external pressure is constant, use w = -P(delta V) with P in atm and V in liters so that you can use the conversion of 101.325 joules per L atm. Then convert q or w to joules or kiloj...

Sofia Barker 2C

The value of Cv for monoatomic particles is 3/2R, and for 2-atom particles it is 5/2R. So U would equal n(3/2)RT for monoatomic particles and n(5/2)RT for 2-atom particles.

Sofia Barker 2C

What was the little saying to remember the state functions other than entropy and enthalpy? The HUGS and TV one? To remember the state functions, the saying was something along the lines of "if you're feeling under Pressure or Depressed, go watch some TV or get HUGS." So the P (pressure) ...

Sofia Barker 2C

Here's an image from Khan Academy that answers your question and explains the signs of W, Q, and delta U.

Sofia Barker 2C

Bomb calorimeters keep volume constant, and since work occurs due to expansion or compression, work equals 0. So delta U is solely in terms of q.

Sofia Barker 2C

Kinetics has to do with the rate of reactions and factors the influence activation energy, like catalysts and heat and such. We have not gone in depth about this concept yet but I'd expect that we will soon.

Sofia Barker 2C

A living plant is considered an open system because it can exchange both energy and matter with its surroundings. Its ability to perform photosynthesis and absorb nutrients from soil are examples of energy and matter exchange.

Sofia Barker 2C

Molar heat capacity increases as the complexity of a molecule increases because complex molecules have more ways to rotate and vibrate, and these motions store heat.

Sofia Barker 2C

I think it would be less confusing if you thought of method 2 (calculating delta H rxn through bond enthalpies) as adding up all the bond enthalpy values for the reactants and products. All bonds broken have positive bond enthalpy values because it takes energy to break those bonds, while all bonds ...

Sofia Barker 2C

Will we be expected to know which bonds do not break when reactants react to form products? I wouldn't have known that the C-H bonds don't break unless someone were to tell me. Is it okay to assume that all bonds of reactants break?

Sofia Barker 2C

I think that those values will be provided on tests and such, but make sure to remember that the standard enthalpy of formation for elements in their most stable form is 0. So pay attention to the phases that certain elements are in because that will indicate whether or not you should look up the va...

Sofia Barker 2C

If bond enthalpies are unavailable, use values of standard enthalpy of formation. The sum of the standard enthalpy of formation of all products subtracted by the sum of the standard enthalpy of formation of all reactants involved in the reaction will give you the total change in enthalpy. For the ex...

Sofia Barker 2C

If the concentration of molecules on one side of a reaction increases, then the reaction will proceed in the direction that would produce the molecules on the other side of the reaction in order to consume the excess and so as to reach equilibrium again. Thus if the concentration of reactants increa...

Sofia Barker 2C

Pressure and concentration do not permanently alter the equilibrium ratio of products to reactants because the reaction will simply shift in response to produce more of the reactants or products until K is once again achieved. Temperature, however, permanently alters K and I believe it is because te...

Sofia Barker 2C

I believe Dr. Lavelle covered autoprotolysis as a way of explaining how 10^-14 = Kw = Ka * Kb, an equation crucial to calculating equilibrium constants and pH / pOH. Other than that, I don't think there's anything else important to know about autoprotolysis.

Sofia Barker 2C

If the partial pressure of one reactant increases, then the partial pressure of the other reactant will decrease (as long as this pressure increase comes from a decrease in volume). Since increasing the pressure causes the concentration of the reactant to increase, the equilibrium will shift to the ...

Sofia Barker 2C

Changing the pressure of a reaction by adding an inert gas has no effect on the concentrations of reactants or products, so the quick way of determining equilibrium shifts doesn't apply. You just need to make sure that the change in pressure causes a change in volume, because that is how concentrati...

Sofia Barker 2C

Yes, the reverse reaction will be favored so as to bring the reaction back to equilibrium by increasing the pressure of the other reactant.

Sofia Barker 2C

When a reaction shifts to the right, this means that there is a higher concentration of reactants than products, so the forward reaction will be favored. (Q<K) When a reaction shifts to the left, this means that there is a higher concentration of products than reactants, so the reverse reaction will...

Sofia Barker 2C

This formula can be used to convert partial pressure to molar concentration. PV = nRT can be rewritten as n/V = P/rT, with n/V representing moles per unit volume, or molarity.

Sofia Barker 2C

Yes, there could be an instance in which a reaction includes reactants or products that are in (aq) and (g) states. If so, you would need to convert partial pressure to concentration through PV = nRT. This equation can be manipulated to n/V = P/RT, in which n/V is molar concentration.

Sofia Barker 2C

Yes, that is okay because it is something that we have recently learned. All of week 1 material is very recent as it is the only material we have learned so far, so it should all be fine to do homework this upcoming week that relates to equilibrium constants.

Sofia Barker 2C

Water is not accounted for because it is considered a pure liquid. Pure liquids don't undergo a change in concentration during a reaction, so it is not necessary to calculate their equilibrium concentrations.

Sofia Barker 2C

Each myoglobin binds to an O2, and four myoglobin make up a hemoglobin. Remember that a heme complex is made up of an iron ion bound to tetradentate porphyrin.

Sofia Barker 2C

Either tetrahedral or square planar will be accepted on the exam.

Sofia Barker 2C

#16 why is the trigonal planar shape considered nonpolar, how did we determine this ? Since it is given that all the "X" atoms are the same, the molecule will be nonpolar because any potential difference in charge between each atom X and the central atom will cancel out due to the symmetr...

Sofia Barker 2C

Joanne Kang 3I wrote:For mini marshmallows 2b, why is the coordination number 4?

The coordination number is 4 because C2O4 is bidentate, which means that it will bind to the transition metal at two sites. These two binding sites along with the bonds formed by the two OH- molecules add up to four total bonds.

Sofia Barker 2C

You are correct. Chelation results from a polydentate ligand binding to a transition metal. A polydentate ligand is able to form a chelate, and a chelating ligand is polydentate, so they are essentially equivalent. Chelating specifically refers to the ring structure formation around a transition met...

Sofia Barker 2C

A chelating ligand is a ligand that can bind to a metal ion at multiple sites. A non-chelating ligand only binds to the metal ion at one site.

Sofia Barker 2C

The longer the bond, the stronger the acid. Long bonds are weak and thus they are easier to break / dissociate easily. Acids that dissociate completely are stronger, and longer bonds make acids most likely to dissociate completely.

Sofia Barker 2C

When looking at a reaction, identify which reactant accepts a hydrogen ion / proton and which reactant donates said hydrogen ion / proton. The molecule accepting the ion / proton is considered a base, whereas the molecule donating the ion / proton is considered an acid. For example, water would be c...

Sofia Barker 2C

Water can act as a Bronsted acid or base because it is capable of donating and accepting H+ ions. H20 can react to become H30+ when it accepts H+ or it can react to become OH- when it donates an H+ ion. Water is thus considered amphoteric because of this duality.

Sofia Barker 2C

Amphiprotic compounds can accept or donate H+ ions specifically, whereas amphoteric compounds can act as both acids and bases without transferring H+ ions. All amphiprotic compounds are amphoteric, but not all amphoteric compounds are amphiprotic.

Sofia Barker 2C

The final will be cumulative but the most recent material we’ve learned will make up a significant portion of the exam.

Sofia Barker 2C

Every lone pair on an electronegative N, O, or F is considered a hydrogen bonding site, so if an N that has a hydrogen bond with a hydrogen still has a lone pair, then that pair is considered a site for hydrogen bonding.

Sofia Barker 2C

Bond angles can be slightly smaller than a given value when at least one region of electron density within the molecule is a lone pair of electrons. Lone pairs have a higher negative charge, so they repel the other regions more than a bonding pair would. This force of repulsion pushes the other regi...

Sofia Barker 2C

T-shape refers to the shape molecules with 5 regions of electron density with 3 bonding pairs of electrons and 2 lone pairs, or the shape of molecules with 6 regions of electron density with 3 bonding pairs of electrons and 3 lone pairs.

Sofia Barker 2C

Remember that the first bond formed is a sigma bond and every bond formed thereafter between the same pair of atoms is a pi bond.

Sofia Barker 2C

There are four regions of electron density in molecules with a trigonal pyramidal shape. Normally, molecules with four regions of electron density have a tetrahedral shape with 109.5-degree bond angles between the 4 bonding electron pairs. However, trigonal pyramidal shapes are formed when one of th...

Sofia Barker 2C

If two dipoles are adjacent to each other, then their combined charge makes the molecule polar. If the dipoles of two of the same atoms lie on the same side of a molecule, this molecule is referred to as "cis." However, if the dipoles of two of the same atom are opposite each other in the ...

Sofia Barker 2C

The bond angles of atoms within a molecule with a trigonal pyramidal shape are less than 109.5 degrees because the lone pair of electrons has greater electron repulsion, so the three bonding pairs are pushed closer together. Lone pairs have greater repulsion because they have a stronger negative cha...

Sofia Barker 2C

"Cis" refers to a molecular structure in which two of the same atoms lie on the same side / plane of a molecule. The dipole moments of these atoms combine and make the molecule polar overall. "Trans" refers to a molecular structure in which two of the same atoms are on opposite s...

Sofia Barker 2C

Homework problems under Chemical Bonding should be fine because it is a recent enough topic. I also think we haven’t technically finished learning everything we need to know under that topic.

Sofia Barker 2C

In order of strongest to weakest bonds: ionic bonds, covalent bonds, hydrogen bonds, van der waals.

Sofia Barker 2C

I was confused by this concept too, but a classmate helped explain to me that when a molecule is larger, there are more electrons and thus more potential intermolecular forces to take place within the molecule. With more electrons, the intermolecular forces will be stronger and this influence distor...

Sofia Barker 2C

The general rule is that, the stronger the intermolecular forces, the harder it is to break them. Thus boiling point is a measure of the strength of forces between atoms in a molecule. The higher the boiling point, the stronger the forces.

Sofia Barker 2C

Why does oxygen have a lower ionization energy than nitrogen? This question was in the homework but doesn’t oxygen having a lower ionization energy violate the periodic trend that ionization energy increases down a period?

Sofia Barker 2C

In general, H, He, and Li want 2 electrons because that satisfies the 1s orbital. Elements in period 3 and any period after can accommodate more than 8 valence electrons because of the d orbitals. Always check formal charge when drawing Lewis structures to confirm that the structure you have drawn i...

Sofia Barker 2C

Hydrogen, Helium, and Lithium will follow a duet rule. This is because their electrons are present the 1s orbital, which is most stable when full (2 electrons). Hydrogen thus wants to gain an electron while Lithium wants to lose an electron in order to have the most stable electron configuration, wh...

Sofia Barker 2C

In order to solve this problem, you must understand the relationship between number of bonds and how that corresponds to strength and length. A single bond is weaker than double or triple bonds because there are fewer electrons being shared and thus a weaker attraction to the positively-charged nucl...

Sofia Barker 2C

The octet rule states that atoms want to form bonds in order to fill its valence shell with 8 electrons and thus reach their most stable form. Filling the valence shell with 8 electrons create an s^2p^6 electron configuration, which is the electron configuration of noble gases. For hydrogen, however...

Sofia Barker 2C

Coordinate covalent bonds are bonds in which the electrons being shared come from the same atom. In a typical covalent bond, such as the bond between two H atoms, each atom provides one electron that both of the atoms can share to fill their 1s shells. In a coordinate covalent bond, such as the bond...

Sofia Barker 2C

The elements in order of increasing electronegativity are indium, tin, antimony, selenium because electronegativity increases up a group and as you move to the right of a period.

Sofia Barker 2C

double and triple bonds are shorter in length than single bonds because the bonds themselves are stronger due to a higher force of attraction between the electrons. The atoms involved in the bonding are thus pulled closer together.

Sofia Barker 2C

Lone pairs are represented as dots, so I think it makes a diagram more clear if the bonds are drawn as lines. However, you can draw them as dots if that makes more sense to you or if it helps you understand the structure better.

Sofia Barker 2C

Covalent bonds are formed between nonmetals because nonmetal atoms are not strong enough to take an electron away from the other atom involved. A covalent bond is simply a bond created by the sharing of electrons between two atoms. Metals form ionic or metallic bonds because they don't have a strong...

Sofia Barker 2C

The goal of manipulating Lewis Structures is to minimize the formal charge of the overall molecule and thus find the most stable form of the molecule. During the lecture example with SO4^2-, we calculated each individual atom's formal charge and then added them all up to see the overall charge, whic...

Sofia Barker 2C

Fe + has the same electron configuration as Mn because Fe + has lost an electron (26 e- minus 1 e- = 25 e-) and thus has 25, the same number as Manganese does. The "+" sign following Fe denotes this loss of electrons because there is a ratio of 26 protons to 25 electrons, giving iron an ov...

Sofia Barker 2C

If all orbitals of an energy level are occupied by single electrons, then these electrons are considered parallel and thus have the same spin. However, once there are two electrons per orbital, these two electrons have opposite spin. These electrons have opposite spin because no two electrons can ha...

Sofia Barker 2C

The Aufbau Principle is based on the Pauli Exclusion Principle and states that electrons occupy orbitals in a way that creates the lowest energy configuration, or the experimentally observed ground state. This means that electrons in an atom will occupy orbitals that maintain the lowest energy level...

Sofia Barker 2C

In order to jump from n =1 to n=2, an electron must absorb enough energy to be able to jump to the higher energy level. Thus the electron's energy does increase because of this energy absorption.

Sofia Barker 2C

Hund's Rule describes the tendency of electrons to want to be in the lowest state of energy, which means minimizing any forces of repulsion. Electrons thus will occupy empty orbitals before occupying an orbital that is occupied by another electron. This rule helps us determine the electron configura...

Sofia Barker 2C

The number of energy levels has no correlation or correspondence with electrostatic force. Electrostatic force is merely the attraction between negatively charged electrons and positively charged protons in an atom, and this force does not dictate how many energy levels an atom has. Rather, the amou...

Sofia Barker 2C

You cannot solve for the molecular formula knowing only the empirical formula unless the problem provides the molar mass of the molecular formula. If this value is not provided, then you cannot solve for the molecular formula. If the value is provided, then compare it to the molar mass of the empiri...

Sofia Barker 2C

43.64% of the first compound is phosphorus so the other 56.36% must be oxygen. Assuming 100-gram sample, divide 43.64g phosphorus by its molar mass (30.974 g/mol) to get 1.409 mol. The mol of oxygen would be 56.36g / 16 g/mol = 3.523 mol. You then divide each of these moles by the smallest mole valu...

Sofia Barker 2C

Balancing the equation allows you to see the molar ratio between butane and carbon dioxide. The balanced equation gives a ratio of 2 moles butane to 8 moles carbon dioxide, so the combustion of 4 moles of butane would produce 16 moles of carbon dioxide according to the 2:8 ratio. 4:16 matches this r...

Sofia Barker 2C

For Test 1, since it is only 7 questions, it is best to understand the methodology behind solving problems like molarity and dilution, limiting reactant problems, balancing equations, mass % composition, empirical vs molecular formulas, and theoretical yield and percent yield. As long as you know wh...

Sofia Barker 2C

The question is asking for the concentration of chloride ions in the solution. The solution is made up of NaCl, KCl, and sugar. Sugars do not contain any chloride ions, thus it is implied that the chloride ions within NaCl and KCl are the only ions to take into account when solving for concentration.

Sofia Barker 2C

You will want to use the equation M = n/v and manipulate it so that M initial = M final, so the equation would then look like n (initial) / v (initial) = n (final) / v (final). This will be helpful for the last step of part A of the problem when you are solving for the final volume after having calc...

Sofia Barker 2C

The test is seven questions long and will take place during your discussion section. It will cover the high school review topics only, which is only what we learned in the 4 modules we had to complete. We can only use a nonprogrammable, nongraphing calculator to solve problems. Doing several homewor...

Sofia Barker 2C

In response to the follow-up question, your example illustrates a problem including an exact figure. In this case, it is known that there is exactly 1 mole of __ being used in the equation, which means that the number 1 has an infinite number of sig figs. Usually, problems will indicate that numbers...

Sofia Barker 2C

Rounding depends entirely on the sig figs of the values presented in the question of the problem. You always want your final answer to reflect the same number of sig figs as the least precise value (the number with the least amount of sig figs) given in the question. For example, when multiplying 15...

Sofia Barker 2C

The question refers to the compound formed by sulfur and the unknown metal.

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