CHEMISTRY COMMUNITY

Samantha Kwock 1D

I believe that both phrases refer to the same equation. The second phrase is just specifying which reactants the rate law applies to.

Samantha Kwock 1D

For first order reactions, the graph of the concentration of reactant vs time is exponentially decaying. However, a linear plot is obtained when graphing the natural log of the reactant concentration vs time.

Samantha Kwock 1D

No, only the slowest elementary step determines the overall reaction rate. The other faster steps before it do not have to be considered when determining the reaction rate.

Samantha Kwock 1D

My TA said that we should know how to derive the rate laws, and that it was fair game for Professor Lavelle to test us on.

Samantha Kwock 1D

With [A] denoting the concentration of a reactant, for first order reactions, the graph of the ln[A] versus time will yield a straight line. For second order reactions, the slope will be linear but for a graph of 1/[A] versus time. For zero order reactions, a linear graph is produced only when graph...

Samantha Kwock 1D

Yes, the negative sign is just to make the reaction rate positive. With respect to reactant concentration, the initial reaction rate will always be negative as reactant is being used up to form product as the reaction progresses.

Samantha Kwock 1D

A chemical reaction gives the overall net change from the reactants to the products. A reaction mechanism gives information about how the products form through certain steps and different collisions.

Samantha Kwock 1D

Zero order reactions have rates that do not vary with changes in reactant concentrations. If the reactant concentration changes but the rate remains the same, then the reaction is zero order.

Samantha Kwock 1D

Instantaneous reaction rate does not take in to account the coefficients of the balanced chemical reaction while the unique rate does. The unique reaction rate is a single value for all the reactants and products while the instantaneous reaction rate can be different depending on which reactant or p...

Samantha Kwock 1D

If you treat the redox reaction like any regular chemical equation and balance it like how you normally would, everything should work out. Do you have a specific example?

Samantha Kwock 1D

If a species is reduced, this means it is gaining electrons. If a species is oxidized, the opposite is true and it loses electrons. A cathode is where reduction occurs and an anode is where oxidation occurs. In a galvanic cell, this transfer of electrons is responsible for creating electrical energy.

Samantha Kwock 1D

This entropy equation can be used to calculate the change in entropy when temperature is constant. For example, you can use this equation to calculate the entropy associated with phase changes because they occur at a constant temperature.

Samantha Kwock 1D

I believe that in class Dr. Lavelle mentioned the change in Gibbs free energy is the energy free to do useful work.

Samantha Kwock 1D

Yes, for K < 1, lnK will be negative, cancelling out the negative in -RTlnK. This means that G is positive. For K > 1, lnK will be positive and G will be negative. When G is negative, the reaction is spontaneous.

Samantha Kwock 1D

The G= G + RTlnQ equation holds true for all reactions, even reactions not at equilibrium. However, for reactions at equilibrium, G=0 and Q=K so G=-RTlnK.

Samantha Kwock 1D

The equation for isothermal, reversible reactions is derived from taking the integral of the change in volume.

Samantha Kwock 1D

Constant volume means that the change in volume is zero. Thus in the work equation, the overall work done would be zero as you would multiply pressure by zero. If volume does not change, then the system does no work,

Samantha Kwock 1D

Heat capacity is defined as the heat required to raise the temperature of an object by 1 degree Celsius while specific heat capacity is the heat required to raise the temperature of one gram of a substance by one degree Celsius. Use specific heat capacity when given the amount of the substance in gr...

Samantha Kwock 1D

A closed system can exchange energy with its surroundings while an isolated system cannot.

Samantha Kwock 1D

Hess's law allows you to add two reaction enthalpies together to determine the reaction enthalpy of a third reaction. If enthalpy were not a state function, its value would be dependent on the pathway it took to form the products. This would then invalidate the method of adding two other reaction en...

Samantha Kwock 1D

Bond enthalpies of diatomic molecules are averages because the bond is identical in all cases, with only two atoms of the same element. For example, with H2 or Cl2. However, for other bond enthalpies, the other chemical species bonded to the atoms affect its energy. For example, for a C-H bond, the ...

Samantha Kwock 1D

The values for bond enthalpy will always be given as a positive value. However, if bonds are being formed instead of broken, then this value will take on a negative sign to indicate this.

Samantha Kwock 1D

The equation to calculate the pH of strong vs weak acids and bases is the same. In both cases pH is equal to the negative log of the H3O+ concentration. However when finding the concentration of hydronium ions, for strong acids, it is assumed that at equilibrium the acid dissociates completely. For ...

Samantha Kwock 1D

The general principle of Le Chatelier is to minimize the effects of the changes done to the system. For increases in pressure, the equilibrium can be thought of as shifting towards the side of the reaction with less moles of gas. An increase in volume would mean a decrease in pressure and concentrat...

Samantha Kwock 1D

The pH of the solution is given as 11.86, so the pOH can be calculated by subtracting from 14 to give pOH=2.14. With this pOH, you can calculate the concentration of OH- ions at equilibrium by taking 10^-2.14, which is approximately 0.00724. The equation for CH3H7NH2's reaction with water is CH3H7NH...

Samantha Kwock 1D

If a reaction is composed of two different reactions, multiply the K constants to determine the K constant of the third reaction.

Samantha Kwock 1D

For example, given three reactions: (1) A + B -> C (2) C -> A + D (3) B -> D The K constants for the reactions would be: (1) K= [C]/[B]*[A] (2) K= [A]*[D]/[C] (3) K = [D]/[B] If you multiply the two K constants together for reaction one and reaction two, you'll find that the [A] and [C] cancel out l...

Samantha Kwock 1D

If the K constant for the weak acid is less than 10^-3, the quadratic equation can be bypassed because the change in concentration is so small compared to the actual initial concentration that it is negligible. After you solve for the equilibrium concentration, if the answer is less than 5% of the i...

Samantha Kwock 1D

If two reactions are added together to form another reaction, then their K constants are multiplied to give the new reaction's K constant.

Samantha Kwock 1D

Decreasing the partial pressure of CO2 would mean that the concentration of CO2 is also decreased. Because the equilibrium is experiencing a removal of reactant, it will shift to form more reactants, thus decreasing the O2 concentration. In a reaction mixture at equilibrium, I am not sure it is poss...

Samantha Kwock 1D

K has no units. In class it was mentioned that concentration estimates chemical activities (a topic more advanced than this course requires), which has no units, and so K also has no units.

Samantha Kwock 1D

There are two types of acids and bases, bronsted and lewis. Bronsted acids are defined as proton donators and bronsted bases as proton acceptors. However, lewis acids are defined as electron acceptors and lewis bases as electron donators.

Samantha Kwock 1D

Without memorizing the charges, one way to tell the charge of the conjugate acid/base is to look at the original compound. For example, for the acid CH6H5OH, the charge is neutral. Thus when this acid gives up its proton (one positive charge), its conjugate base takes on a negative charge. In your o...

Samantha Kwock 1D

An acid and a super acid follow the same chemical principles, but a super acid can dissolve more hydrogen ions in solution such that its pH is outside of the "normal" pH range (0-14) and is negative. Likewise, super bases have pHs larger than 14.

Samantha Kwock 1D

The example is saying that the composition of the C-H sigma bond is one sp2 hybridized orbital from carbon and one s orbital from hydrogen. These two orbitals make up that specific sigma bond.

Samantha Kwock 1D

CH2Cl2 may appear nonpolar from the Lewis structure, but since its VSEPR structure is tetrahedral, the Cl dipole moments do not cancel each other.

Samantha Kwock 1D

All sigma bonds are hybridized as sigma bonds are defined as single bonds between two atoms created by the hybridization of their orbitals. In order for a sigma bond to be formed, hybrid orbitals must be created. Pi bonds are not hybridized as they are composed of the overlap between two atoms' p or...

Samantha Kwock 1D

After drawing the Lewis structure and determining the VSEPR shape, the bond angle can be determined from the shape. Each VSEPR shape has certain bond angles associated with the shape. Part (b) is linear because the Lewis structure consists of Be bonded to two CH3 groups. The central atom Be only has...

Samantha Kwock 1D

sp2 orbitals should be used when there are three regions of electron density in a molecule. sp3 orbitals should be used when there are four regions of electron density in a molecule. sp orbitals are used when there are only two regions of electron density. sp4 does not exist, to create five bonding ...

Samantha Kwock 1D

For C2H4, the most stable Lewis structure consists of two carbon atoms double bonded to each other and two hydrogens bonded to each of the carbons. For each carbon, there are three atoms bonded to it, which gives it the shape of trigonal planar. The trigonal planar shape has bond angles of 120 degre...

Samantha Kwock 1D

One usage of the number of sigma and pi bonds is that it can determine the rotation of the molecule/ its rigidity. The more pi bonds a molecule has, the less rotation it will be able to perform.

Samantha Kwock 1D

No, it depends on the electronegativity differences between the atoms involved in the bond. If the electronegativity difference between the two atoms involved in the bond is small, then the bond is non-polar and its arrangement around the central atom does not matter.

Samantha Kwock 1D

Tetrahedral geometry requires four atoms bonded to a central atom. Trigonal planar only has three atoms bonded to the central atom.

Samantha Kwock 1D

Actual yield can be experimentally determined, but I think in most, if not all cases, actual yield will just be given.

Samantha Kwock 1D

The dashes and wedges are used to represent atoms in 3-D space. If you can imagine your paper as a plane, the dash lines show atoms going backwards behind the plane and the wedges show atoms sticking out towards you.

Samantha Kwock 1D

H2S is polar. While the lewis structure is symmetrical, in 3-D space, the two lone pairs on the Sulfur atom repel the bonding electrons, which results in a bent shape (we haven't went over this in class yet). This bent shape has a dipole moment with a partial positive charge on the Hydrogens and a p...

Samantha Kwock 1D

I believe that should be the right answer as the two electrons that would be removed due to the 2+ positive charge on Ni would be the two electrons in the 4s orbital.

Samantha Kwock 1D

I think the term"highly distorted" electrons is referring to the electron cloud surrounding the anion participating in an ionic bond. If the bonded cation's charge attracts the electrons from the anion, the electron cloud becomes "distorted," and the anion is described as being h...

Samantha Kwock 1D

The placement of the other atoms around the central atom shouldn't matter because Lewis structures are only 2-D models of bonding. In 3-D space, the molecule will take on a specific structure that will dictate the placement of the atoms.

Samantha Kwock 1D

Linear momentum p can also be defined as mass times velocity. In the uncertainty principle equation, the uncertainty in linear momentum can be substituted with the expression m times the uncertainty in velocity. In this context, the linear momentum is important because as an object's velocity is mea...

Samantha Kwock 1D

In the case of (NH4)+ and (SO4)2-, (NH4)+ only has a full valence shell because it gave up one of its electrons, generating a positive charge and (SO4)2- only has a full valence shell because it stole two electrons, generating the negative 2 charge. Cations and anions form ionic bonds through this t...

Samantha Kwock 1D

"Zeff" refers to effective nuclear charge. Zeff is not independent of the number of electrons in an atom because as the number of electrons increase, the inner electrons "shield" the outer electrons from experiencing the full effects of the nucleus' positive charge. Thus, as the ...

Samantha Kwock 1D

"px, py, and pz" describe the orientation of the lobes of the p orbitals. For the px orbital, the two lobes lie along the x axis. For the py orbital, the lobes lie along the y axis. For the pz orbital, the lobes lie along the z axis.

Samantha Kwock 1D

The ultraviolet spectrum, or the Lyman series, involves electron transitions from a higher energy level to n=1. The wavelength of the emitted light can be converted into frequency. This frequency can then be used in conjunction with Rydberg's equation to determine the value of the second principal q...

Samantha Kwock 1D

I believe that the main idea he was trying to convey is that the higher the nuclear charge is (for Carbon it would be 6+ because it has 6 protons in the nucleus), the greater the attraction between the electrons and the nucleus. The overall idea presented is that electrostatic attraction grows with ...

Samantha Kwock 1D

I believe that the Balmer series only refers to transitions that end in n=2, but n=2 is not considered the ground state of the electron. If an electron is at n=2, it is still considered excited.

Samantha Kwock 1D

The minimum frequency needed to be absorbed by molybdenum metal can be converted into energy using E=hv. This energy is the same as the metal's threshold energy. Similarly, the 194 nm of light can be converted into energy using the E=hv equation, this is the energy of the light photon. The maximum k...

Samantha Kwock 1D

The DeBroglie equation is used to calculate the wavelength of any moving particle. However, as mentioned in class, all matter has wavelike properties, but this can only be measured for objects with small masses, such as electrons.

Samantha Kwock 1D

I'm not sure if this is the cause of your problems with part b, but copper (II) hydroxide should have the chemical formula of Cu(OH)2.

Samantha Kwock 1D

This is similar to what was said in class. Imagine you are running three trials of an experiment that require you to measure out a certain number of grams of an element. The balance that you use could give measurements numerically close to each other all three times. If this is the case, then the ba...

Samantha Kwock 1D

I believe that Avogadro's number is typically rounded off to 6.022 x 10^23.

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