CHEMISTRY COMMUNITY

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Instantaneous rate is the rate of the reaction at a particular time.
Average rate is the rate of the reaction over the time taken to the reaction's completion

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The unique reaction rate is defined as the rate of the increase in product concentration or the rate in decrease of product concentration divided by the stoichiometric coefficient.

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This is because k is associated with how fast a reaction runs. If the reaction runs faster then the amount of time needed for the substance to fall to half its original decreases. Hence, K is inversely proportional to Half life.

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The oxidizing agent always oxidizes the other substance and gets reduced.
The reducing agent always reduces the other substance and gets oxidized.

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You always flip the anode reaction. You can usually determine the anode reaction by choosing the reaction which has the lowest reduction potential (more negative and less positive)

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it is always anode then cathode. According to Dr Lavelle, we have to also put states in the following manner- solids on the outside and aqueous in the middle.

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What exactly is Gibbs free energy? (conceptually speaking)

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5/2 R= C when the pressure is constant
3/2 R= C when the volume is constant

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This can only be said when pressure is constant since q(at constant pressure)= delta H

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It tells us about spontaneity of a reaction, work and can be used to calculate the equilibrium constant.

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G is always in terms of Joules. But the equation G=nFE is molarly dependent. Thus, the units are slightly different. But essentially, the conceptual idea is the same.

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Yes. We will have to know how to predict spontaneity based on the values. Sign of the enthalpy change Sign of the entropy change Spontaneity positive (+) positive (+) The reaction is spontaneous at high temperature positive (+) negative (-) The reaction is never spontaneous negative (-) negative (-)...

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Yes. But spontaneity is largely dependent on the 3 factors: enthalpy change, entropy change and temperature. Based on the values of each, the gibbs free energy is either positive or negative. Usually, however, exothermic reactions are more likely to be spontaneous because is H is less than 0, and si...

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This equation does apply to every system. However, when we consider solids and liquids, change in volume is essentially 0 (Dr. Lavelle described this in lecture). Hence P(V final- V initial) is 0 and does not affect systems with solid and liquids.

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Essentially, boiling water at 100 degrees celcius, becomes steam at 100 degrees celcius when it overcomes the latent heat of vaporization. Hence, when skin is exposed to steam, it absorbs more heat from steam as it fist needs to lose the heat of vaporization and convert back to water at 100 degrees....

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Bond formation is exothermic while bond breaking is exothermic. Hence, when bonds are formed, since they release energy, we put a negative sign before the values.

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It depends on the situation. When considering a free reaction, we consider kJ since that is the exact amount of energy being released or absorbed. But, when we consider the situation where in we are considering a standard reaction (ex: Haber's process for 1 mol of ammonia), then we write kJ mol-1 to...

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How do we calculate the pH of polyprotic acids with very small second or third Ka values? And how small should they be?

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Yes. Dr. Lavelle gave us a couple in 7a. We should remember those.

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No. The values will be given on the test.

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No, because 10^-4= Kw at 298K is an experimentally determined value.

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True. Professor Lavelle referred to these acids as super acids.

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Le Chatelier's principle states that a system will respond to change in a means to minimize the effect of the change. That means that the system tries to reverse the effect to return to what it was (essentially). For example, increases the concentration of products causes the Q value to increase. To...

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Because that would indicate that the products and reactants are in the same ratio. Essentially, in the real world, that would be rare.

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As temperature increases, the molecules of gas have more energy and begin striking the walls of a container with higher frequency. Essentially, the molecules exhibit a higher pressure on the container since they attempt to further themselves from each other.

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R is the ideal gas constant 8.314 J/(K mol)

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Bar and atm are the same. They can be interchanged.

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Kp is used when the substances are gaseous. But Kc can be used when the substances are gaseous or aqueous.

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No difference. It's the same but K is when equilibrium is achieved. Q is at any point of the reaction.

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Weak acids do not completely dissociate and thus the proton yield is lower. Consequently, the pH is higher than for a strong acid which almost always dissociate completely and yields higher proton concentration.

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Strong acids almost always dissociate completely to yield hydronium ions.

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Lewis acids are electron pair acceptors.

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It refers to one ligand that can form multiple coordinate bonds with the central metal ion. Ex: EDTA

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Test 3 covers: End of Bonding from 3.12 (6 Ed.) and from 2D (7 Ed.); and all of Molecular Shape and Structure

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Ethylene is formed from a sp2 hybridization of carbon and the arrangement on the orbitals are in the triangular planar. The angles are thus all 120 degrees.

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Sigma bonds are formed when orbitals overlap head on, along the bond axis. Pi bonds are formed when the ortibals overlap above and below the bond axis.

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Ionic bonds are stronger since they are the electrostatic force of attraction between positively and negatively charged ions. Hydrogen bonds are weaker since they are between dipoles (partially charged regions of a molecule).

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Angular shape can exist in two forms: 1) 3 regions of electron density (1 lone pair and 2 bonded pairs- Sulfur dioxide)- it has a bond angle of less than 120 (around 117) 2) 4 regions of electron density (2 lone pairs and 2 bonded pairs- dihydrogen monoxide)- it has a bond angle of less than 109.5 (...

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Molecular shape is dependent on the areas of electron density around the central atom. It can be divided into two categories: 1. Bonded pairs (single, double and triple) 2. Lone pairs The repulsion affects the shape further: lone-lone> lone-bonded> bonded-bonded These are the main features that affe...

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Bond angles are dependent on the number of lone pairs and bonding pairs around the central atom. Bonding pairs are less repelled by one another than from lone pairs. When we take Methane for example, there are 4 bonding pairs around the carbon and to space themselves out maximally, they form a tetra...

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Single bonds are the weakest since only one electron pair is being shared. Thus, the force of attraction between the nucleus and the shared pair is low. However, with double bonds, the area of electron density is much more dense/strong since more number of electrons are being shared and thus the for...

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Hydrogen bonds by definition only form when hydrogen is directly bonded to N, F and O. The electronegativity difference in sulphur and hydrogen is much lower than that of hydrogen and oxygen. Hydrogen sulphide, thus, is less polar and the dipole formed are weaker than in water. Thus, a hydrogen bond...

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They can only be determined experimentally. However, the relative bond lengths can be determined by the electronegativity differences between the elements participating in the bond (carbon-fluorine bonds have a shorter bond length than carbon-bromine bonds)

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Electronegativity is the tendency of an atom of an element to attract electrons towards itself when bonded. Polarizability is the tendency to be polarized (electrons can be 'distorted' by other atoms) Generally substances with high electronegativity has a tendency to be less polarized (since the ele...

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Yes, every atom can exhibit london dispersion forces because it is due to the essentially random movement of electrons in an atom resulting in the formation of a temporary dipole.

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Electron affinity is calculated for gaseous atoms (the energy change when an electron is added to the gaseous atom) and its unit is kJ/mol. This is experimentally derived. Electronegativity is the tendency of an atom to attract electrons towards in a bonded state and is for bonded atoms only. It is ...

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This is because phosphorous can utilize the d orbitals and, thus, has an expanded octet.

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Naming works pretty easily. The name of the cation always comes before the name of the anion. Most cations would be the name of the metal (sodium, lithium, calcium, etc.) The name of the anion is variable: Halogens would end in "ide" (fluoride, chloride, bromide, etc) The same applies for ...

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How do we determine the number of significant figures to use in the exam?

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How do we draw the lewis structure of HClO3?

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Why can xenon extend to more number of electrons through expanded octet than chlorine?

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Why are sigma bonds stronger than pi bonds?

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Because the second ionization energy is the removal of the electron from a cation which has a stronger pull on the electron than the neutral atom.

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h bar is h/2pi

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Shielding is when electrons in lower energy levels "shielding" or preventing the nuclear charge from reaching electrons in outer shells. Thus, when there are more number of orbitals, there is more shielding on the outer electrons.

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There is not much to be known for this course. In each orbital, 2 electrons can exist and they take up opposite spins. They take the values 1/2 and -1/2 since there's 50% chance of up spin and 50% chance of down spin.

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Do we have to know how to solve the wave functions for the orbitals?

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The black body radiation refers to the idea that a body which absorbs all frequencies of light of the electromagnetic spectrum. It also happens to not only be the ideal absorber of light but the ideal emitter (ex: a star) - emitting light of all frequencies.

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The uncertainty principle works on the idea that both the momentum and the location of an electron cannot be known at once. When one is known, the other can be calculated but not known in that point of time. Thus, when we calculate anything regarding the uncertainty, its a range of possibilities (he...

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It would be preferred to stick to Joules since the entire equation focuses on generating the amount of energy needed to for the photoelectric effect.

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Light acts like both a wave and a particle. Depending on the situation, for questions in class, we tend to adopt the wave or particle model which fits a particular explanation.

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I think it would be advisable to have a general idea, like Dr. Lavelle said, about where a particular wavelength falls.
100-400 nm: UV light
400-700 nm: Visible light
700 nm- 1 mm: Infrared radiation

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Yes. The photon of the incident light must have sufficient energy such that it exceeds or equals the work function. Only then, will the electron have sufficient energy to be ionized and get released to be detected and produce the photoelectric effect.

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Isotopes are atoms of the same elements but have different mass numbers or different number of protons!

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Epsom salts consist of magnesium sulfate heptahydrate. Write its formula. a) How many atoms of oxygen are in 5.15g of Epsom salts? b) How many formula units of the compound are present in 5.15g? c) How many moles of water molecules are in 5.15 g of Epsom salts? Answers: a) no. of moles of magnesium ...

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From an experimental chemistry standpoint, an example of accuracy vs. precision would be: If we conducted an experiment to test the volumes of carbon dioxide released when different concentrations of acid were added to metal carbonates, the study would have- 1. Low accuracy and Low precision if the ...

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