CHEMISTRY COMMUNITY

AnuPanneerselvam1H

If a reaction is first order then the rate will be doubled when the reactant is doubled. If the reaction is second order and only has one reactant, then doubling the reactant will cause the rate to be squared.

AnuPanneerselvam1H

K of reaction step 2 can equal k2/k'2. The equilibrium applies to all equations and is a ratio of forward rate reaction constant to reverse rate reaction constant.

AnuPanneerselvam1H

No, just make sure to match T1 with k1 and T2 with k2

AnuPanneerselvam1H

While these are common units for these types of problems, it does not have to be these units specifically. Use whatever is consistent with the problem.

AnuPanneerselvam1H

My TA mentioned that for problems in this class, n will always be close to a whole number.

AnuPanneerselvam1H

negative k for zero and first order reaction rates and positive k for second order reaction rates

AnuPanneerselvam1H

No the rate law is determined from experimental data.

AnuPanneerselvam1H

Each reaction has a unique rate. A higher k means a faster reaction and a lower k means a slower reaction. When you multiply k times the concentrations in the rate law, you get the unique reaction rate for the specific reaction.

AnuPanneerselvam1H

Most problems keep k in terms of seconds however it is ok to convert to other units if needed for the problem.

AnuPanneerselvam1H

Since the stoichiometric coefficients are 2 for NO2 and 1 for O2, the rate of O2 production will be half of that of NO2 depletion.

AnuPanneerselvam1H

A higher activation energy means there is a higher energy barrier for the reaction. This means more energy is needed for the reaction to proceed which will require a longer amount of time in most cases.

AnuPanneerselvam1H

Yes the reaction rate will change as the reaction proceeds. We will always take the instantaneous rate closest to t=0 since this is the maximum rate.

AnuPanneerselvam1H

Electrochemical cells generate electrical energy from chemical reactions. Galvanic cells are a type of electrochemical cell that generate electricity through redox reactions.

AnuPanneerselvam1H

Oxidation number of an atom in a neutral compound is zero when the substance contains only one element. So O2 and O3 would have an overall charge of zero.

AnuPanneerselvam1H

The anode is where oxidation occurs. In this case the Zinc is being oxidized. The Zinc is also referred to as the reducing agent since it is being oxidized

AnuPanneerselvam1H

Specific heat capacity is an extensive value and depends on the amount of substance present. Standard cell potential is an intensive value and does not depend on the amount of substance present.

AnuPanneerselvam1H

Even if the diagram does not show a salt bridge, I think it is safe to assume that there is a salt bridge in all redox reactions. If there were no salt bridge there would be a buildup of elections in the cathode and after a certain point, electron flow would stop because of the charge buildup. By ha...

AnuPanneerselvam1H

Yes, when you flip a reduction equation, you are basically running the reverse reaction, which is oxidation. You will also need to take the negative of the standard reduction potential.

AnuPanneerselvam1H

Spontaneity is determined by multiplying temperature (in kelvin) and enthalpy and subtracting this from entropy. If this value is negative, the reaction is spontaneous.

AnuPanneerselvam1H

Yes you can subtract the enthalpies of formation of reactants from the enthalpies of formation of reactants since enthalpy is a state function (path is independent from final and initial state).

AnuPanneerselvam1H

Heat capacity is an extensive property and does not necessarily have trends in the periodic table. It is the amount of heat required to raise 1 mole/gram of substance by 1 degree Celsius/Kelvin. Therefore, it depends on intermolecular forces

AnuPanneerselvam1H

Degeneracy is the amount of states a particles can exist in. Entropy is a measure of disorder in a system. While they both may seem similar, degeneracy is describing the actual number of states and entropy is measured in J/K

AnuPanneerselvam1H

Entropy is calculated by dividing the heat lost/gained in a reversible reaction divided by the temperature of the system. If this reaction occurs at constant pressure then you can substitute q for delta H, or enthalpy change.

AnuPanneerselvam1H

Degeneracy is the number of ways of achieving a given energy state. An example given in class was that a quarter has a degeneracy of 2 since it can either land on heads or tails. The higher the entropy, the higher amount of possible energy states.

AnuPanneerselvam1H

This depends on the initial and final temperatures of the system. If the system goes from -10 degrees Celsius to 50 degrees Celsius, you need to calculate
mCdeltaT for -10 degrees to 0 degrees + phase change from ice to liquid + mCdeltaT for 0 degrees to 50 degrees

AnuPanneerselvam1H

We will be given bond enthalpies and we will have to determine reaction enthalpy depending on which bonds are broken and which bonds are formed.

AnuPanneerselvam1H

Delta U is a summation of the work done in the system and the heat in the system. In other words, it is a measure of the internal energy of the system. When pressure is constant, there is no work being done. Therefore delta U is equal to delta H under these circumstances.

AnuPanneerselvam1H

No it does not have to be at this temperature but most reactions happens at 25 degrees Celsius

AnuPanneerselvam1H

Yes we learned three methods. The first one involves Hess's Law, the second one uses bond enthalpies, and the third one uses standard enthalpies of formation. The method you use depends on the information given.

AnuPanneerselvam1H

Temperature stays constant during a phase change because the heat is being used to break/make bonds between the molecules.

AnuPanneerselvam1H

Strong acids will have more electronegative/electron withdrawing atoms in their formulas. This will allow the proton to break away more easily and for the resulting anion to be stable.

AnuPanneerselvam1H

Acetic acid only loses the hydrogen that is attached to the oxygen because of oxygen's electronegativity. The nonpolar bond between carbon and hydrogen prevents the hydrogens from being donated since electrons are equally shared.

AnuPanneerselvam1H

Ka is the acidity constant, or the equilibrium constant of an acid dissociation equation. It is a ratio of the products concentration to the reactants concentration. On the other hand, [H3O+] is the concentration of hydronium ions and is measured by pH.

AnuPanneerselvam1H

In respect to oxacids, acids with a greater amount of oxygen will be stronger because the electrons of the resulting anion are more delocalized. This is due to the high electronegativity of oxygen.

AnuPanneerselvam1H

You can calculate %dissociation of an acid by dividing the conjugate base concentration by the initial acid concentration. This is a measurement of how much the acid dissociates.

AnuPanneerselvam1H

How do you determine whether is amphoteric by looking at its formula? Are all compounds with metalloids considered amphoteric?

AnuPanneerselvam1H

Coordination Number is simply the number of ligands attached to the transition metal. The transition metals contain s,p, and d orbitals and can therefore accommodate many ligands.

AnuPanneerselvam1H

When calculating the concentrations of products/reactants, we can approximate if the equilibrium constant is very small (<10^-5). This does not x is zero, but that x is very small and has a negligible effect.

AnuPanneerselvam1H

pKa and pH are different. Ka is the equilibrium constant for a reaction that involves an acid. pKa = -log(Ka). pH is a measure of how strong the acid is (how much it disassociates. pH = -log[H+]

AnuPanneerselvam1H

Since Ba(OH)2 is a strong base, we know it completely disassociates. For every one mole of Ba(OH)2 that is diasassociated, there will be one mole of Ba+ and two moles of OH-. Therefore we multiply the base's concentration by two to get the concentration of OH-. From here we can calculate pOH

AnuPanneerselvam1H

Since water is the solvent, it's concentration will barely be affected. Therefore it is not included in the equilibrium ratio.

AnuPanneerselvam1H

Since the atomic radius decreases across a period, the energy required to remove an electron becomes higher. Therefore, ionization energy increases from left to right across a periodic table. Chlorine is to the right of beryllium and so it has a higher ionization energy.

AnuPanneerselvam1H

I think we will mostly be asked to draw lewis structures to figure out the bonds and areas of high electron density. From VSEPR we will probably be asked to identify molecular structure and bond angles.

AnuPanneerselvam1H

The 4s orbital is filed first because it is lower in energy compared to the 3d orbital. The lowest energy state is always preferred. Another example of this is with the Chromium and copper examples. The electron in the 4s orbital will move to the 3d orbital in order to the evenly fill the orbitals, ...

AnuPanneerselvam1H

We don't need to know the shapes since we will not be asked to draw them, but it helps to be able to visualize them. For example, the p orbitals have nodes, where no electrons will be found (probability density is zero here). The s orbitals do not have any nodes and electron density is more evenly s...

AnuPanneerselvam1H

The electron spin number can be either +1/2 or -1/2. This just tell us whether the electron is spinning clockwise or counterclockwise.

AnuPanneerselvam1H

Hund's Rule states that due to electron repulsion, electrons in the same subshell occupy different orbitals with parallel spin. This allows for the lowest possible energy state. There are no more than two electrons per orbital. If 2 electrons are in the same orbital they are spin paired.

AnuPanneerselvam1H

1.6022 x 10^-19 J/eV is a ratio that is used to convert between the two units since most equations use Energy in Joules. Also I think k stands for kilo in this case. Therefore it would be 1.6022 x 10^-16J/ keV

AnuPanneerselvam1H

I agree, technically the answer should be 6.0 x 10^-7 so that the the number of sig figs remains two. They wrote it as 600 nm so that we can see the wavelength is part of the visible light spectrum.

AnuPanneerselvam1H

1800. only has 4 sig figs if there is a decimal. Without the decimal, there are only two sig figs. In this case, it would be 1.80 x 10^3 for 3 sig figs.

AnuPanneerselvam1H

If the answer is .1 away from a whole number, round accordingly. If it isn't then multiply all mole ratios so they are close enough to whole numbers. For example, if one ratio is 2.25, multiply all the ratios by 4 to get whole numbers.

AnuPanneerselvam1H

A reactant is a substance that is consumed in the creation of a product in a chemical reaction. A reagent is used to detect, measure, or produce other substances. In other words, a reagent is a more passive reactant (could be a catalyst?). But for the most part, I believe these words can be used int...

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