CHEMISTRY COMMUNITY

monikac4k

Usually, the problem will tell us which steps are fast and which step is slow. Then with that information, we can solve for the overall rate law.

monikac4k

What I did was use the half-life in order to find the k value (t1/2= ln2/k). Then I would just use the integrated rate law to solve for the time required for the other scenarios. For example, when it asks for 15% of the initial concentration, you would plug in 0.15A0 into [A] and then solve. Althoug...

monikac4k

Homogenous reactions are when all the products and reactants are in the same phase. Heterogeneous reactions are when the products and reactants are not all the same phase.

monikac4k

Since the rates of formation/consumption for reactants and products are different due to their stoichiometric coefficients, the unique rate takes the stoichiometric coefficients into consideration to give us a rate that works overall rather than for a specific reactant or product.

monikac4k

You might want to have a basic understanding of how the equations are derived. You mainly just need to know that you set the rate law in the form k[A]^n equal to the rate law in the form -d[A]/dt and solve.

monikac4k

Usually, some sort of experimental data will be given to us so that we can figure out what order the reactants are.

monikac4k

When finding n, you would want to solve for both the oxidation and the reduction half reactions. Once you get there, see how many moles of electrons are transferred in the completely balanced redox reaction; this number of moles is the number you want to use for n.

monikac4k

In general, the more complex the molecule is, the higher the entropy because it can be rearranged in many different positions.

monikac4k

Standard cell potentials give us information on how badly a compound wants to be reduced. The more positive the cell potential of the reduction reaction, the more the compound will serve as the oxidizing agent (reduction reaction). The more negative the cell potential of the reduction reaction, the ...

monikac4k

For a Galvanic cell, reduction occurs at the cathode, meaning the substance is gaining electrons. At an anode, oxidation is occurring, and the substance is losing electrons. These two reactions, oxidation and reduction, are paired through the Galvanic cell, meaning that the electrons lost from the a...

monikac4k

Entropy always increases as a substance goes from solid to liquid to gas because as the intermolecular forces break, the molecules can move around and occupy more positions. Gas will have more entropy than a liquid.

monikac4k

The degree symbol indicates that the reaction is occurring under standard conditions (usually 25 degrees Celsius, 1 bar pressure, etc.).

monikac4k

Whenever using the ideal gas equation (pv=rnt) we want to use the R constant with units of L*atm*mol^-1*K^-1 because the units will cancel. When solving for work or entropy, we usually use the one that 8.314 J/mol*K because the units cancel out and leave us with J. In order to be absolutely sure, ju...

monikac4k

We usually use Boltzmann's equation when a problem gives us a number of molecules and the number of positions each molecule can possess. This is because, given this information, we can find degeneracy (W).

monikac4k

When a system is isothermal, the change in internal energy is zero.

monikac4k

Hey Kirsty! When the change in pressure is 0, both q and w should be considered when calculating the change in internal energy of the system. However, when the change in volume is 0, we can only focus on q. Remember that the calculation for work is dependent upon the change in volume times the exter...

monikac4k

Heat capacity is the amount of energy (in the form of heat) required to raise the temperature of a specific substance one degree C. e.g. the amount of energy required to raise the temperature of a sample of water is 4.184 J*g^-1*C^-1. The enthalpy of vaporization is the amount of energy (in the form...

monikac4k

The following is problem 103 from the 6th edition textbook: Calculate the molar kinetic energy (in joules per mole) of Kr(g) at (a) 55.85 C and (b) 54.85 C. (c) The difference between the answers to parts (a) and (b) is the energy per mole that it takes to raise the temperature of Kr(g) by 1.00 C. T...

monikac4k

I assume this formula would be used while the pressure and the volume are both changing at the same time. In this scenario, the pressure is no longer constant and the area underneath the pressure-volume curve wouldn't be a simple box. For complex functions modeling changes in pressure, calculus is r...

monikac4k

Some reactions, usually exothermic reactions, occur spontaneously and are favored. There is no work forcing the reaction to occur and not heat is put into the system. Instead, the system will react on its own, releasing energy as heat. This is similar to a boulder rolling down a hill. Gravity does a...

monikac4k

Cv is used when the reaction is being conducted at constant volume and Cp is used when the reaction is being conducted with constant pressure.

monikac4k

If a weak acid deprotonates and releases less than 10^-7 M of hydronium, then you would consider autoprotolysis. This is because if you ignore autolysis and calculate pH of an acid that creates 10^-9 M hydronium, then the pH would be basic. This would not make sense since there is an acid in the sol...

monikac4k

H2SO4 is a polyprotic acid. When it loses the first hydrogen, the reaction is strong since it completely dissociates into HSO4- and H+. The second dissociation isn't so complete; HSO4- is a weak acid and has a Ka value.

monikac4k

Ice tables usually come up when we are asked to find the concentrations of products and reactants at equilibrium, but the problem only gives us the initial conditions.

monikac4k

When there is a change in pressure, the volume of the system is usually changing; the amount of matter in the reaction vessel remains the same, but the amount of space (volume) that the matter takes up is partially related to the pressure being placed upon the matter. It is important to notice that ...

monikac4k

When dealing with aqueous solutions with water as the solvent, we would not include water in the equilibrium constant because it is in excess. However, some equilibrium reactions include water in a gaseous phase. In this case, water would be included when solving for K.

monikac4k

R is a constant and I believe it will be given to us for tests (???). T represents temperature in Kelvin. In order for us to use the ideal gas law to convert between pressures and concentrations, we will usually be given the temperature in the problem. It may also be handy to remember the conversion...

monikac4k

I am pretty sure that the problem will specify whether we need to calculate kc or kp. It should be made explicit for us.

monikac4k

I assume intermediate values are comparable to reactions with a k value of 1. When k is close to one, such as the intermediate values, the ratio of products to reactants is nearly identical. This would imply that the reaction doesn't favor either the forward reaction or the reverse reaction.

monikac4k

I am pretty sure that for the purposes of this course we will only be working with coordination complexes with one TM. Usually, these transition metals have a positive oxidation state, therefore they will only form coordinate covalent bonds with molecules and/or atoms that have negative dipoles or n...

monikac4k

If one of the ions in the salt is also an acid, then when the salt is added to water, the acidic ion will also react with the water. NaCl doesn't do this because neither Na+ or Cl- are acidic. Professor Lavelle used the example NH4Cl in class to demonstrate this to us because the NH4+ ion is acidic ...

monikac4k

Latin names are used when the element symbol is derived from its Latin name and the overall coordination sphere has a negative charge. Some examples would be ferrate for iron (Fe), cuprate for copper (Cu), plumbate for lead(Pb), argentate for silver(Ag), aurate for gold (Au), and stannate for tin (S...

monikac4k

It depends on the model being used. The original model points towards the partial negative charge with a plus at the end by the partial negative. The modern model just points towards the partial positive charge. Howeverm I'm not entirely sure which convention is more proper for this course.

monikac4k

Square pyramidal shapes are the results of a octahedral electron arangement with one lone pair. The lone pair takes the place of one of the polar atoms. The resulting shape is the central atom with one polar atom and 4 equatorial atoms in a square pyramidal shape.

monikac4k

Is one definition preferred over the other? Or are the two definitions equally interchangeable?

monikac4k

As we learned the wave function numbers and their meaning we learned that we are dealing with a d orbital when l=2. For l to equal 2 the value of n must be at least 3. This means elements in the 3rd period possess a d sub-shell. However, we also learned that the electron configuration for an element...

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Dipole forces occur as a result of uneven electron sharing between two bonded atoms. For example in water, the oxygen pulls the electrons closer to it than the hydrogen atoms do. London forces occur between atoms without dipole moments. When in a proximity of one another, atoms without dipole moment...

monikac4k

What is the official name of a molecule with 3 ligands and 2 lone pairs around the central atom?

monikac4k

A good analogy for me to understand polarizability is to compare it to malleability. Polarizability, from my understanding, is how likely an atom or molecule's electron cloud will shift in response to another electromagnetic force. Malleability is a substance's ability to change form and mold into a...

monikac4k

If a molecule is already experiencing a dipole moment, where one area is slightly negative and another is slightly positive, then these minor charges will cause a shift in the electron cloud of nearby molecules. If a molecule (let's call it A) is near a positively charged region of another molecule ...

monikac4k

Adding onto the other two comments, sometimes you will notice that at a certain point, the ionization energy from one electron to the next will make a very large jump for an atom. Take magnesium for example. Just as the others had said, the second electron requires more energy to be removed in compa...

monikac4k

The long formula for formula charge is: FC= (valence electrons) - (# lone pair electrons + (# of shared electrons / 2 ) ) The best way I can think of shortening this is by swapping (# of shared electrons / 2 ) with just the number of Lewis lines that signify bonds since each bond line represents 2 e...

monikac4k

The key to this is following Hund's Rule for electron configurations. We know there are 8 electrons on the 3d subshell. We also know there are 5 orbitals in the d subshell (5 possible ml values; accommodates 10 electrons). First, we can place one electron in each of the 5 orbitals. 3d: ^ ^ ^ ^ ^ Now...

monikac4k

I'm not too sure about if there is a correct way of doing it, but I usually put brackets around both ions when drawing the Lewis structures.

monikac4k

I haven't taken the test yet, but from my understanding, we are supposed to know the lowest energy level and the type of electromagnetic radiation each series represents.

monikac4k

Similarly to how Professor Lavelle describes the d-orbitals as lagging by 1 period, the f-orbitals lag by 2 periods. Just as the person before me stated, the 4f orbital is placed in the same period as the 6s orbital.

monikac4k

Can somebody clarify the importance of recognizing that multiple ions can be isoelectronic? I know that isoelectronic ions don't necessarily have the same chemical properties. Do we just need to understand that they carry the same number of electrons?

monikac4k

Similarly to how we know that ml=-1 in the p-orbital would mean that the orbital is aligned on the x axis, would we need to know what each ml number in the d orbital corresponds to? And if so, what orientation corresponds with each ml number?

monikac4k

I'm pretty sure that Prof. Lavelle said that it is important to understand the concepts behind the equation, but we wouldn't be expected to use it for any calculations. Such calculations are grad level work.

monikac4k

It is best to break down the units of a joule when you are also trying to calculate energy. Often times problems will try to trick you by giving velocity in miles/hour or they will give you mass in grams. When you approach a problem like this, it is important to know that you need values in kg and m...

monikac4k

I know other people already gave good explanations for the units of a joule, but I wanted to share a way to sort of remember the units. When I took AP Physics in high school, my teacher told us a little phrase to remember the units: "Newton, meter (meet her). She's a Joule (jewel)!" From p...

monikac4k

Hi, I am a bit confused with the idea of taking the length of the spectroscopic line and working backwards to find the beginning and ending energy levels of the electron. This confusion comes from problem 15 in chapter 1 of the 6th edition textbook. However, I want to understand this type of problem...

monikac4k

After an electron is ejected from the metal, they will gravitate towards the detector because the detector has a slightly positive charge and the election has a negative charge. The detector is also connected to the metal, allowing the electron to make its way back to the metal. I assume the loss of...

monikac4k

Another example would be a titration lab. If you were to repeat the titration lab and continued to use about the same volume of the titrant in order to activate the indicator for each trial, then your lab would have a precise set of trials. However, your lab trials would only be accurate if the stan...

monikac4k

If the number of moles is the answer to the problem, you would want to round according to the number of sigfigs, which in this case seems to be 4 significant figures. However, if you are going to continue using the number in further calculations, you should continue using the longer version. Accordi...

monikac4k

While working on the textbook problems, I came across problems asking for formula units. I am still confused about what a formula unit is. Can somebody please explain it to me and how to find it?

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