CHEMISTRY COMMUNITY

Kayli Choy 2F

I know that catalysts increase the rate of the forward reaction by providing a new pathway with a lower activation energy, but why do catalysts also increase the rate of the reverse reaction?

Kayli Choy 2F

How can you tell whether something is a catalyst in a reaction mechanism? What about an intermediate?

Kayli Choy 2F

If you are given rate constants, you can also figure out whether a reaction is zero, first, or second order:
zero order: k = M/time
first order: 1/time
second order: 1/ (M * time)

Kayli Choy 2F

Furthermore, for first order reactions, the linear graph would be ln[A] vs. t, and for second order reactions, the linear graph would be 1/[A] vs. t.

Kayli Choy 2F

Because the units for k are different for zero, first, and second order reactions, if you are only given k and concentrations and are looking for the reaction rate, you would automatically know the order of the reaction.

Kayli Choy 2F

Additionally, the substance being reduced (oxidation number becoming more negative) is the oxidizing agent (because it is allowing the other substance to be oxidized). The substance being oxidized (oxidation number becoming more positive) is the reducing agent (because it is allowing the other subst...

Kayli Choy 2F

Additionally, you can tell that a substance is being oxidized when the oxidation number of the substance increases (this is the reducing agent). A substance is being reduced when the oxidation number of the substance decreases (this is the oxidation agent).

Kayli Choy 2F

You would add H2O first in order to balance the oxygen molecules. Then, you would add H+ ions to balance out the hydrogen molecules, and then add electrons to balance charge.

Kayli Choy 2F

To add on, when balancing reactions in acidic solutions, you can use H2O to balance the oxygen molecules, and H3O+ to balance the hydrogen molecules. When balancing reactions in basic solutions, you would use H2O and OH- ions.

Kayli Choy 2F

Additionally, when oxidation number of the reactant increases (becomes more positive), that is the substance that is being oxidized. When the oxidation number of the reactant decreases (becomes more negative), that is the substance being reduced.

Kayli Choy 2F

If you have a half-reaction and both the products and reactants are aqueous, then you would need a platinum electrode.

Kayli Choy 2F

For something to be reduced, it must gain electrons. Therefore, a donor of electrons is needed. This electron donor is giving electrons to reduce something else, therefore allowing reduction to occur (reducing agent). If this electron donor were not present, reduction could not occur. However, the e...

Kayli Choy 2F

When finding Estandard, you usually take Estandard(cathode) - Estandard(anode), but in a concentration cell, because the two reactions are the reverse of each other, their Estandard values cancel out, so you get Estandard(cathode) - Estandard(anode) = 0 = Estandard.

Kayli Choy 2F

The Nernst equation is Ecell = Estandard - ((RT) / (nF)) * ln(K), if you are given Estandard and the chemical equations, and you know that at equilibrium, Ecell = 0, then you can manipulate the equation to become: ((- Estandard)*(nF)) / (RT) = ln(K) and if the value on the right is positive, then yo...

Kayli Choy 2F

DLee_1L wrote:Just to clarify, when calculating Q and K, we combine the concentration and partial pressures? or is there some conversion we have to do?

Yes, as long as all concentrations are in M, and partial pressures are in atm.

Kayli Choy 2F

Additionally, an oxidizing agent is the thing being reduced, so oxidation number decreases. A reducing agent is the thing being oxidized, so oxidation number increases.

Kayli Choy 2F

Additionally, if a reactant’s oxidation number is increasing, the reactant is being oxidized, and if the oxidation number is decreasing, it is being reduced.

Kayli Choy 2F

If a reactant’s oxidation number is increasing, it is being oxidized and is therefore the reducing agent. If a reactant’s oxidation number is decreasing, it is being reduced and is therefore the oxidizing agent.

Kayli Choy 2F

Additionally, you use H3O+ to balance reactions in acidic conditions, and you use H2O and OH- to balance reactions in basic conditions

Kayli Choy 2F

Additionally, the double line in the middle of the cell diagram represents the salt bridge, while the single lines represent interfaces.

Kayli Choy 2F

Work = -(pressure)(FinalVolume - InitialVolume). Therefore, if your final volume is greater than your initial volume (gas expands) then your change in volume will be positive, so this is why work will be negative. Additionally if your initial volume is greater than your final volume (gas is compress...

Kayli Choy 2F

Additionally, if the problem says a reaction is isobaric, that implies that pressure is constant. If a reaction is isochoric, isovolumetric, or isometric, that implies that volume is constant.

Kayli Choy 2F

Additionally, for isothermal reversible reactions, delta S total = 0, so delta S = -delta S(surroundings). For isothermal irreversible reactions, delta S(surroundings) = 0, so delta S total = delta S, and the entropy of the universe increases

Kayli Choy 2F

2 is obtained by subtracting total moles of product (5) by total moles of reactants (3) based on the chemical reaction. You would then divide that number of moles by 4 because you are trying to find the internal energy when one mole of CO2 is produced, but the current reaction produces 4 moles of CO2

Kayli Choy 2F

Additionally, isochoric/isovolumetric/isometric all mean constant volume, isobaric means constant pressure, and isothermal means constant temperature.

Kayli Choy 2F

For W = X^N, X = number of microstates, and N = number of particles. A good textbook problem demonstrating this concept is "4G.1 Nanotechnologists have found ways to create and manipulate structures containing only a few molecules. However, orient- ing the molecules in specific ways to assemble...

Kayli Choy 2F

Additionally, molar heat capacity is an intensive property because it is not dependent on the amount of substance you have.

Kayli Choy 2F

Additionally for this equation, if you need to find work and you are given pressure and change in volume, w = -Pexternal(delta V), and you can substitute this in for w in the larger equation of delta U = q + w. If q = 0, no heat is being added, and if w = 0, no work is being done on the system.

Kayli Choy 2F

Furthermore, enthalpy is a state property, which means that it is not dependent on the path take to obtain that state. Therefore, you can add/subtract enthalpies to find the total change in enthalpy.

Kayli Choy 2F

I think the correct way to think about it is
-(heat given off by the system reaction) = (heat absorbed by the surroundings)
Because the system is losing heat, there is a negative in front of it, and because the surroundings are gaining heat, that value is positive.

Kayli Choy 2F

Essentially, water requires requires a large heat input (large heat of vaporization) in order to vaporize, so the steam absorbs that heat energy, causing it to burn more than just boiled water at 100 degrees. The water does not have that additional heat that the steam has because energy has been inp...

Kayli Choy 2F

Additionally, if the change in internal energy is positive, then final internal energy is larger than initial internal energy. If the change in internal energy is negative, final internal energy is smaller than initial internal energy. The energy of a closed system can be altered by heating/cooling ...

Kayli Choy 2F

Additionally, a bomb calorimeter is a special type of calorimeter where the volume is held constant, and a reaction occurs in a vessel of water. The temperature of the entire assembly is then monitored, because the heat gained by the surrounding water is equal to the heat released by the reaction.

Kayli Choy 2F

Work (w) and heat (q) can both contribute to change in internal energy of a system (the equation is delta U = q + w). Work is a force done on or by the system, whereas heat is the thermal energy transferred due to a change in temperature.

Kayli Choy 2F

Additionally, more heat energy is required to break bonds when a substance is vaporizing (liquid to gas) as opposed to when a substance is melting (solid to liquid) because bonds have to be completely broken in the gas phase.

Kayli Choy 2F

Additionally, the greater the Ka, the smaller the pKa, and the stronger the acid. The greater the Kb, the smaller the pKb, and the stronger the base.

Kayli Choy 2F

Could someone explain why steam is so hot and carries more heat than boiled water? I know it might have something to do with the specific heat of vaporization.

Thank you!

Kayli Choy 2F

Bond formation is typically exothermic (condensation, freezing, deposition), and bond breaking is typically endothermic (melting, vaporizing, sublimation).

Kayli Choy 2F

ShastaB4C wrote:Can someone give me an example of a property that is dependent on the path taken besides work?

Heat is also a path function because the energy transferred as heat depends on how that change occurred.

Kayli Choy 2F

Closed systems can exchange energy in the form of heat, but it cannot exchange matter. For instance, a closed beaker can exchange heat with its surroundings, but not the matter inside of the beaker.

Kayli Choy 2F

Yes, you would set up the ICE chart as normal, with .22 bar being the value for HCL, and when you find x, the units for that are also in bar.

Kayli Choy 2F

Additionally, calculating Q is important because it can be compared to K in order to determine the direction the reaction is proceeding. When Q=K, the reaction is at equilibrium composition.

Kayli Choy 2F

For the ICE tables , if the product side has 2 moles that are both the reactants combined, would the x value be 2x because its doubling in moles? I am assuming you mean: A + B --> 2C ? If so, then yes, when you are setting up the ICE chart, on the reactants side, there would be two +x's, and on the...

Kayli Choy 2F

If you need to calculate Q, then if Q < K, reaction will proceed in the direction of the products (forward) if Q > K, reaction will proceed in the direction of the reactants (reverse). Additionally, if there is a Ka value for the forward reaction, then 1/Ka would be the equilibrium constant for the ...

Kayli Choy 2F

Additionally, since this problem is asking for Q, you must then divide those mole values by the volume (.500 L), and then use those concentrations to calculate Q = [SO3]^2 / ( [O2] * [SO2]^2 ).

Kayli Choy 2F

5G.9: "A sample of ozone, O3, amounting to 0.10 mol, is placed in a sealed container of volume 1.0 L and the reaction 2 O3(g) S 3 O2(g) is allowed to reach equilibrium. Then 0.50 mol O3 is placed in a second container of volume 1.0 L at the same temperature and allowed to reach equilibrium. Wit...

Kayli Choy 2F

I believe that gases are always included because they contribute to partial pressures, which are important in calculating K if the equilibrium is all gaseous.

Kayli Choy 2F

The reaction quotient, Q, is calculated in the same way in which K is calculated. If Q < K, the reaction is proceeding forward, toward products. If Q > K, the reaction is proceeding in reverse, toward reactants.

Kayli Choy 2F

Furthermore, if the concentrations of reactants are increased, the equilibrium will shift to the right and create more product to compensate, and if the concentrations of products are increased, the equilibrium will shift to the left and create more reactants to compensate. As stated above, this is ...

Kayli Choy 2F

Additionally, if
- Q<K, the reaction will proceed forward to create more products
- Q>K, the reaction will proceed in reverse to create more reactants

Kayli Choy 2F

A structure has delocalized electrons when it has resonance structures. You can tell if a Lewis structure has resonance structures if a double bond can be placed in multiple different places without affecting the number of valence electrons the molecule must have.

Kayli Choy 2F

Resonance structures are theoretical and drawn out when drawing Lewis structures. In resonance structures, the actual structure of the molecule is not changing, but the position of electrons is. If a molecule has resonance structures, this means that its actual structure is a blend of all of its res...

Kayli Choy 2F

This equation is called De Broglie's equation, and can be used because all particles show some form of wave-like properties.

Kayli Choy 2F

Additionally, for the Arrhenius definition, Arrhenius acids react with water to produce H+, and Arrhenius bases react with water to produce OH-.

Kayli Choy 2F

K+ (aq) would be on both sides of the equation because it does not interact or affect water in any way. Therefore, it does not need to be included when writing the net ionic equation.

Kayli Choy 2F

In this problem, you are finding the change in pH values so you could set up the equation:
(change in pH) = -log(1) - (-log(.12))

You are using 1 and .12 because the HCl is reduced to only 12% of its initial value.

Hope this helps!

Kayli Choy 2F

Arrhenius acid: reacts with water to produce H+
Arrhenius base: reacts with water to produce OH-
Bronsted acid: donates protons
Bronsted base: accepts protons
Lewis acid: electron pair acceptor
Lewis base: electron pair donator

Kayli Choy 2F

Additionally, the conjugate acid works the same way. The conjugate acid of a base is the compound formed when the base accepts a proton.

Kayli Choy 2F

For binary acids (H + an element A), the higher the electronegativity of A, the stronger the acid. Acid strengths down a group correlate with bond strength as well.

Kayli Choy 2F

For binary acids (H + an element A), the higher the electronegativity of the element A, the stronger the acid. Acid strengths down a group correlate with bond strength. For oxoacids, the greater the electronegativity of the halogen, the stronger the acid, and the more oxygens attached to the central...

Kayli Choy 2F

Just to clarify further, stronger dispersion forces will indicate that the compound is more likely to be a solid/liquid, have a higher boiling point, and a higher melting point?

Kayli Choy 2F

The proof that all compounds, even nonpolar ones, have IMFs is that nonpolar compounds can be liquefied.

Kayli Choy 2F

If there is one compound with weak dipole-dipole interactions, and another compound with a large molar mass and many electrons (so therefore strong London Dispersion Forces), which one would have the greater boiling point? Is it possible that strong LDFs can result in a higher boiling point that a c...

Kayli Choy 2F

What is dissociation energy, and what factors in IMFs contribute to a larger or smaller dissociation energy?

Kayli Choy 2F

What is the relationship between the strength of London Dispersion Forces and melting point?

Kayli Choy 2F

Yes, bond angles are between any three atoms in the molecule. Remember that sometimes, if there are lone pairs, angles will be slightly less than they would be if there were no lone pairs. This is due to repulsion.

Kayli Choy 2F

For instance, rod shaped molecules have stronger IMFs because there are more places of contact than spherical molecules.

Kayli Choy 2F

Additionally, small, highly charged cations like Al3+ have a large polarizing power, which means that they are able to strongly distort electron clouds.

Kayli Choy 2F

There are times where lone pairs are opposite each other, and the repulsive forces cancel each other out. For instance, in molecules that have trigonal bipyramidal electron arrangement (6 bonding spots), with bonded atoms and 2 lone pairs, the lone pairs on the top and bottom of the molecule cancel ...

Kayli Choy 2F

Lewis structures are not representative of molecular shape, so even if the molecules are drawn with 90 degree angles, this does not mean that the bond angles are 90 degrees. Therefore, either way works for the Lewis structure.

Kayli Choy 2F

Magnetic quantum number distinguishes individual orbitals in the subshell (the orientation of an electron). The allowed values for magnetic quantum number are the integers from -l to l (where l is the orbital angular momentum quantum number)

Kayli Choy 2F

Additionally, in this equation, the energy is negative because when an electron drops from a higher energy level to a lower energy level, energy is released in the form of a photon.

Kayli Choy 2F

All objects have wave-like properties to an extent, but waves with wavelengths larger than 10^-15m are observable, so objects with wavelengths that are larger than 10^-15m have observable wave-like properties. Objects with a tiny mass and fast speed (like electrons, protons, etc.) have observable wa...

Kayli Choy 2F

The De Broglie equation is
wavelength = h / [(mass of particle in kg) * (velocity of particle in m/s)]
Using the De Broglie wavelength, you can use the equation speed = wavelength * frequency to find the frequency.

Kayli Choy 2F

Additionally, the particle model of light is evident through the photoelectric effect experiment, where individual photons of light with enough energy are able to eject electrons from metals. The wave model of light is evident through the doubles-slit experiment, where light produces a diffraction p...

Kayli Choy 2F

Additionally, formal charge is calculated through the formula FC = V - (L + .5B), where V is number of valence electrons, L is number of lone electrons, and B is number of bonding electrons.

Kayli Choy 2F

The atom in the middle is often the one with lowest ionization energy because the central atom shares more electrons, and an atom with higher ionization energy would be less likely to share more electrons.

Kayli Choy 2F

Additionally, if your molecule has resonance and you are drawing Lewis structures for the resonant structures, calculate the formal charge of each atom in each resonant structure. The Lewis structure that has atoms with formal charges closest to zero represents the lowest energy arrangement.

Kayli Choy 2F

Additionally, if your molecule is charged, the sums each of the formal charges of the atoms should equal the total charge of the molecule. The Lewis structure in which formal charges of individual atoms are closest to zero represents the lowest energy arrangement.

Kayli Choy 2F

When ions are separated by large distances, as they are in the gas phase, there is attraction between them (potential energy). As the ions get closer together, this attraction lessens. Therefore, there is a net lowering of energy, and when ions get close enough together to form a solid, energy is re...

Kayli Choy 2F

What is the difference between a shell, a subshell and an orbital? Are the terms subshell and orbital interchangeable?

Kayli Choy 2F

Furthermore, spin up electrons are typically denoted with a spin magnetic quantum number (m_s) of +1/2, and spin down electrons are -1/2.

Kayli Choy 2F

Additionally, there is also an m_s quantum number (spin magnetic quantum number) that specifies the spin state of the electron. m_s can be either +1/2 or -1/2. The four quantum numbers together can specify an electron and its spin state.

Kayli Choy 2F

For c, if n=2, that means that the possible orbitals are
n = 1, l = 0
and
n = 2, l = 1
n = 2, l = 0
n = 2, l = 1
because the allowed values of l are -(n-1) to (n-1).
Therefore, there are four possible orbitals for n=2.

Kayli Choy 2F

Additionally, principal quantum number (n) specifies the size and energy level the electron is in, while angular momentum quantum level specifies the shape of the orbital.

Kayli Choy 2F

During the photoelectric experiment, light was acting as a particle. When the intensity of light was increased, only the number of photons increased. However, each photon still did not have sufficient energy to eject an electron. When the frequency of the light was increased, the energy of each phot...

Kayli Choy 2F

Another experiment that demonstrated the wave-like properties of electrons was when electrons were passed through a crystal lattice, and a diffraction pattern resulted. This led de Broglie to believe that all particles with momentum have wave-like and particle-like properties, but the wave-like prop...

Kayli Choy 2F

An electron-volt (eV) is a unit of energy that is equal to the energy an electron gains after being accelerated across 1 volt. This unit is typically used when discussing energy on an atomic/sub-atomic level (very small amounts of energy).

Kayli Choy 2F

Additionally, E=hv is commonly used with c=λv if you are given energy and want to find wavelength, or vice versa. If you solved for v, you would get v=c/λ, which you could plug into E=hv to get E=(hc)/λ.

Kayli Choy 2F

To add on, constructive interference is when wave peaks coincide, and the overall wave amplitude increases. Destructive interference is when a trough coincides with a peak, and the overall wave amplitude decreases. Because the double slit experiment gives rise to diffraction patterns, it demonstrate...

Kayli Choy 2F

Can someone explain the details of how if you decrease the intensity of light it doesn't decrease the amount of energy or something? I'm so confused about the minute instances of that. When light is acting as a particle (like it is during the photoelectric effect experiment), the intensity of light...

Kayli Choy 2F

In contrast, intensity with respect to particle properties is proportional to the number of photons. The higher the intensity, the more protons are present.

Kayli Choy 2F

To add on, you would use the equation E=hv because this equation calculates the energy of a photon. In order for an electron to be ejected, the incoming photon's energy must be equal to or greater than the energy needed to remove the electron (work function). Therefore, finding the minimum energy of...

Kayli Choy 2F

Additionally, electrons can only absorb or emit certain discrete packets, or quanta, of energy. This means that only when an electron absorbs a certain amount of energy will it jump up to the next energy level. And since electrons can only emit certain amounts of energy, they will only emit the spec...

Kayli Choy 2F

Additionally, an example of an experiment that proves the wave model of light is the double-slit experiment. Light was shone through two double slits, and a diffraction pattern was observed. This diffraction pattern was created due to the constructive and destructive interference patterns of waves. ...

Kayli Choy 2F

I believe M i V i = M f V f would still apply. Since you want to find out how much water is needed, you are finding V f , so V f = (M i V i ) / M f You are going from a concentration of 50% glucose to 20%, so we can choose the hypothetical values of .5 M and .2 M for our M i and M f . You begin with...

Kayli Choy 2F

Additionally, since the number of moles in dilutions remains the same, let n = moles n i = n f and since Molarity = n / V (where V = volume in Liters) you can say that M i V i = M f V f This is the main equation used in dilution problems, where V is volume of the total solution. From this equation, ...

Kayli Choy 2F

Most gaseous mixtures are also homogeneous because there is a uniform distribution of elements throughout the gas. For example, air is a homogeneous gaseous mixture that contains oxygen, nitrogen, carbon dioxide, and other elements all well-mixed together.

Kayli Choy 2F

Additionally, whenever the problem states that the reaction is a combustion, burning, or complete oxidation, you know that O2 (g) will be one of the reactants, and that this reaction will release CO2 and H2O. These types of reactions all release energy. If there is incomplete oxidation, CO (carbon m...

Kayli Choy 2F

Hi Ashley, In writing CuSO4 + H2O --> products, you are saying that CuSO4 is reacting with H2O to form products. However, I believe CuSO4.5H2O is a complete compound itself, so the CuSO4 is not reacting with water to form any products; the 5H2O just refers to the fact that the CuSO4 is hydrated, and...

Search found 100 matches