CHEMISTRY COMMUNITY

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Through graphing the Arrhenius equation, we can see that the slope of the Arrhenius plot is proportional to the activation energy. A higher activation energy indicates a stronger temperature dependence of the rate constant.

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A catalyst needs to be there in the beginning of reaction to start reaction off. The intermediate will not appear in the beginning of a reaction because it is not a reactant. It is both formed and consumed so that it does not appear in the overall chemical equation.

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Thermodynamics explains whether or not a reaction will occur while kinetics explains the speed of a reaction. They are very intertwined and related to each other.

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The intermediate is both formed and consumed in the reaction but does not appear in the overall chemical equation.

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If used correctly, the experiments that you choose to use should yield the same result. In other cases, there are only certain experiments that can be used to determine what the question is asking.

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Also, if you are given the elementary steps of a reaction, you may be able to determine the order of a reaction.

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Dr. Lavelle also noted the difference between intermediates and catalysts in which catalysts are initially there and then reformed while intermediates are created and consumed in the reaction.

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A bimolecular can have two different molecules interacting (A and B) or 2 of the same molecule interacting (A). The rate laws would be k[A][B] and k[A]^2 respectively.

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Half life is the time needed for concentration to fall to half its initial value. Half life is independent of initial concentration but is inversely related to the rate constant.

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Also, A varies by reaction but is mostly independent of temperature.

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Since molecules need to collide at the correct orientation in order to react, orientation must be accounted for in the Arrhenius equation. This dependence on orientation leads to less molecules reacting than if we only accounted for collisions based on kinetic energy.

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Endothermic and exothermic reactions both have an activation energy. But for endothermic reactions, the products have higher energy than the reactants and for exothermic reactions, the products have lower energy than the reactants.

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Since termolecular was all that was discussed in class, I think so. Especially since termolecular reactions are already fairly uncommon since it requires 3 molecules to simultaneously collide.

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Catalysts lower the activation barrier, so a greater fraction of reactants can cross the new lower barrier and convert into products.

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The molecule involved in the slow step is what determines the rate generally.

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fYou can always solve the units for k by dividing the units for rate (mol x L^-1 x s^-1) by the units of your concentrations (which depend on the order of the reaction).

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Also, for termolecular reactions, the 3 molecules must simultaneously collide, so termolecular reactions are less common.

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They will likely be on the formula sheet, but if you do need to derive the formula, plug in t=1/2 to get the half life formula.

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The units should be the same so that they will cancel out when doing calculations. Also, sometimes, the question will ask for the answer in a particular unit.

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You should get the same rate constant for different experiments if your rate law is correct. You can also do it for multiple experiments if you want to check your answers.

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Rate constants will be positive, but you can still get a graph with a negative slope, such as in 1st order reactions where the slope is -k.

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Masses and concentrations are proportional. Through using the equation ln[A]t/[A]0, = -kt, we find that the proportion of [A]t to [A]0 is 1/10. So, 10% of the initial drug concentration remains in the body, which is (0.10)(20 mg) = 2.0 mg.

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Also, remember to use H+ and H2O to balance acidic solutions and OH- and H2O to balance basic solutions.

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Also, for cell diagrams, the cathode will be depicted on the right, even if the cell reaction is not spontaneous in that direction.

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The oxidizing agent is what is causing something else to be oxidized. So, it itself will be reduced in order for this to happen. The same is true for the reducing agent.

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In acidic solutions, the concentration of hydronium ions that the concentration of hydroxide ions so H+ should be used to properly balance the half-rxns. So, for basic solutions, OH- should be used because this is the ion that is at a higher concentration in the solution.

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This way, we can also more clearly see which atoms are being reduced and oxidized and make sure the movement of electrons is accurate.

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I think we only need to know how to use them, but the derivations can be helpful in understanding the concepts behind the equations.

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Yes, because one of the equations for delta G depends on Q.

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Which equation you use can tell you different things about Gibbs free energy. Look at the different variables in each equation and use what is applicable based on the question.

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The entropy and enthalpy are different at different temperatures but their delta's are the same.

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The vant hoff equation can be used to calculate K at different temperatures if stand enthalpy of real lion is known.

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Both are probably acceptable for the final answer but we may have to convert in order to do the calculations because only certain units are compatible with certain constants or values (like heat capacity)

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Also, if you keep track of units, it makes it easier to do any calculations you may need.

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yes, because the reaction would have more heat to absorb from the surroundings. Therefore, you can think of it as heat not being a limiting reactant.

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The heat capacity is the constant of proportionality between heat supplied to a system and temperature rise that results.

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The equation delta U = q + w works because both heat and work are equivalent means of energy transfer.

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Also, if w = 0, the internal energy of the system is determined only by q. If q = 0, the internal energy of the system is determined only by w.

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Reversible reactions in thermodynamics refer to thermal equilibrium when the temperature of the system and surroundings is the same. Thermal equilibrium is dynamic and responsive to change, even infinitesimal.

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the sign of w indicates whether work is being done on the system or the system is working. Remember that the sign of work is in relation to the system.

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Remember that the sign for work is always in regard to the system. In expansion, the system is doing the work and is therefore losing energy so work is negative. In compression, work is being done on the system, so work will be a positive value.

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I don't think we have to memorize actual values but we will have to know what they mean.

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You can also look at the temperature change of the surroundings and use that to conclude whether the reaction is exothermic or endothermic. If a reaction is exothermic, it releases heat into surroundings. If a reaction is endothermic, it absorbs heat from the surroundings.

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The system is the region of interest and the surroundings is everything else. So, in these cases, the thermometer and the engine would be the systems. Everything else would be the surroundings.

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A state function is a property that depends only on the current state of a system, independent on how the state was prepared. For example, internal energy, pressure, volume, temp, and density are state functions. Work and heat are not.

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Also, heat and work are equivalent means of energy transfer and are the only to change the internal energy of a system.

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Also, the first law of thermodynamics states that the internal energy of an isolated system is constant. This would not be true for an open system where the system can exchange both matter and energy with the surroundings.

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whether we leave out water in the ICE table is dependent on the question, so make sure to read the chemical equation carefully.

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The % ionization is the concentration of the molecule in the ionized state divided by the concentration of the molecule in the unionized state. If this is less than 5%, not a significant amount of the molecule ionized compared to the initial concentration.

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water is not included in the K constant when it is a solvent because it is viewed as pure. Liquids and solids are not included in the K constant since their concentrations do not significantly change.

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Pressure and volume are inversely proportional because conceptually, the smaller the volume/space, the less room the gases have and therefore the higher the pressure.

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it is also helpful to know that if there is a strong acid, it will have a weak conjugate base and a strong base will have a weak conjugate acid. Therefore, by knowing the strength of the conjugate, we can determine the strength of the acid or base.

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Bidentate is a form of polydentate. Polydentate can also refer to tridentate, tetradentate. Chelating are polydentate, but polydentate is not necessarily chelating.

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You only use the Latin name + ate when the overall charge of the compound is negative.

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Each Cl inside the bracket is one negative. But also there are 2 Cl, each one negative, for a combination of -4. So, Pt must have an oxidation number of 4 for the total complex to be neutral.

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Both the abbreviation and the full names are acceptable for naming.

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We should know cisplatin and how its shape affects its function

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A coordination compound is an electrically neutral compound, in which at least 1 of the ions is a complex of a central metal with other molecules attached.

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Also, the -ate is added to the stem of the metal's name. For example, iron would be named ferrate.

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The roman numerals refer to the oxidation number of the central metal atom or ion. It can be determined by finding the difference between the charges of the ligands and the overall charge of the molecule.

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Anything that is outside the brackets is not bound to the central metal atom or ion.

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en is bidentate, meaning it has two binding sites, so each en will contribute a coordination number of 2. edta is hexadentate, so it has 6 binding sites.

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i think the anionic ligands end in -o. And if the anion ends in -ide, it becomes -ido, -ate becomes -ato, and -ite becomes -ito.

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A metallocene is a "sandwich compound" in which the ligands act as the outside pieces or "bread" and the metal atom is the "filling"

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Additionally, sometimes the -ate is added to the stem of the metal's name not the metal name as it appears on the periodic table. For example, iron is denoted ferrate.

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If you know the charges of the other ligands or anions, and the overall charge of the molecule, you can figure out the oxidation state of the transition metal because it must add up to the overall charge.

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A ligand is a a Lewis base attached to the central metal atom/ion. Each ligand typically has at least 1 lone pair, which forms a coordinate covalent bond with the metal.

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Boiling points increase as the strength of the intermolecular forces increases. For example, a molecule with Hydrogen bonds will likely have a higher boiling point than a molecule with only induced dipole forces because the Hydrogen bonds require more energy to break. Higher temperatures have more e...

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The bond angle would be less than 109.5 because the lone pair repulsion is greater than bonding pair repulsion.

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Also, with enough practice, you can remember how many lone pairs and bonding pairs like to have. For example, Oxygen likes to have 2 lone pairs and 2 bonding pairs because this gives it a formal charge of zero.

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The formal charges don't necessarily have to be zero, but you should try to minimize formal charge as much as possible for a more stable molecule.

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The dipoles will cancel if they are in opposite direction and of same magnitude. They will be same magnitude if they involve the same atoms. If the dipoles cancel, the resulting molecule will be non polar with polar bonds.

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Lone pairs do influence molecule shape but only atom positions are used to name the shape.

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Yes, because the molecule still has dipoles. What makes the molecule non polar overall is likely that the dipoles cancel out.

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A polar molecule must have polar bonds and dimples that do not cancel. A non polar molecule must have zero electric dipole moment.

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It did say in the textbook that a single bond would not be three times longer than a triple bond or a single bond would not be two times longer than a single bond.

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I think we should just know between two molecules with different interactions, we should be able to dictate which molecule will have the higher boiling and melting point. Typically, it will be the molecule with the stronger interactions that will have higher boiling and melting points.

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When a cation exerts an electrostatic attraction on the electrons surrounding the anion, the anion's electrons are pulled into the Bonding region/internuclear area. When there is electron density in the region between the nuclei, the spherical electron cloud of the anion is no longer spherical due t...

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Electronegativity has the same trend as electron affinity. However, the mathematical definition of electronegativity is Ionization Energy + Electron Affinity divided by two. In other words, electronegativity is the average between ionization energy and electron affinity.

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Breaking a bond requires energy since bound atoms have lower energy than free atoms. Therefore, forming a bond releases energy.

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I went to a review session, and the TA said that you can either draw all the structures and explain that the actual structure is a hybrid or for example, if it is a double bond resonance, you can draw a single line and a dotted line for the second bond to represent the resonance.

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Also, you can check which Lewis structure has the lowest energy by checking the formal charges. You want the most neutral/nonzero charges as possible.

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The threshold frequency is synonymous with work function, which is the Energy needed to remove an electron. However, each individual photon must reach this threshold frequency, dependent on wavelength, not intensity. Therefore, light is acting like a particle, not like in the wave model.

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Also, while this isn't directly related to what you asked, also remember that energy is conserved in a reaction as well.

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Normally, the higher the percent yield (the closer to 100%), the better the experiment because that means not much reaction was stuck to the side or involved in side reactions.

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The fact that the decimal is purposefully placed in the number means that you must count the zeroes after the decimal as significant. The power of 10 is not counted when considering significant figures.

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Also, clarifying the state of molecules can be important for molecules like water, that can exist in multiple forms.

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Dr. Lavelle regularly uses the Angstrom to describe bond length in lecture so I think this is a good indicator that is an important unit to know, even if it is not an SI unit.

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It may also be good to know the general trends of EM radiation. For example, gamma rays have short wavelength and high frequency while radio waves have long wavelength and low frequency with visible light in the middle.

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Combining equations will often be necessary as you normally will not have all the requirements for a certain equation given to you easily. Practicing combining equations will help you recognize when to combine.

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The equation E=hv can also easily be rearranged to be used to solve for v as well if you know Energy. Planck's constant will always be the same.

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Electrons have higher energy when they are at a higher energy level because it requires more energy for them to be farther from the positive pull of the nucleus.

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Is electron affinity the same as electronegativity?

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Also, electron repulsion before the first electron was removed helps keep the ionization energy lower. Once the first electron is removed, there will be less electron repulsion, so the electron will be even harder to remove.

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Also, no two electrons can have the same four quantum numbers. If two electrons share the first three quantum numbers (n, l, ml), their spins must be different. One will be +1/2 while the other will be -1/2.

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If one property is known, the other cannot be known simultaneously. For example, if one knows the position of an electron, it is impossible to simultaneously know the momentum.

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Electrons should have the same mass in all the elements. The same goes for protons and neutrons. It is the number of each that affects the overall mass of the atom.

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Also, when balancing equations, you can check your work when you're done to make sure you did it right. This has helped me catch errors multiple times.

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I think we just need to know the general trends of electronegativity across the periodic table. For example, electronegativity increases across a period due to the increased number of protons in nucleus.

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Half filled subshells and full filled subshells are more stable. For the d subshell, having 5 or 10 electrons in the subshell is favorable because it is a lower energy state.

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