CHEMISTRY COMMUNITY

Brian Chhoy 4I

Work is usually reported in Joules, so the 101.325 J/L*atm would most likely be used when you are converting the value gained from an irreversible expansion. The units of the value gained from using the equation to calculate the work done from a reversible expansion is already in the units of joules...

Brian Chhoy 4I

You would use a derived version of the Arrhenius equation: ln(k2/k1)= (Ea/R) ((1/T1)-(1/T2)). Solving for k2, since you are given the rest of the information needed for the rest of the equation.

Brian Chhoy 4I

The maximum work that a cell can do is equal to the change in Gibbs free energy of the cell.

Brian Chhoy 4I

Lavelle says that it is not likely that we would get a non-integer order, since that is not common in natural reactions. You might get one that is a few decimal points off ( 1.97), thus you would just assume this is from experimental errors and round to 2.

Brian Chhoy 4I

Yes, the unique average rate of reaction for each product/reactant is the same, as long as you know the change concentrations of each substance, the corresponding coefficient, and the change in time.

Brian Chhoy 4I

They just represents how much they affect the reaction rate. Thus zeroth order has no effect, first has and effect proportional to the change to the reactant, and second has an affect proportional to the change raised to the second power. It is a number that relates the rate of the chemical reaction...

Brian Chhoy 4I

The unique average rate of a reaction is just the rate of a reaction but put in terms that the rate of change of a specific reactant or product of the reaction are all equal to each other. Dividing by their coefficients and making sure to make the rate of change of the reactants negative, each indiv...

Brian Chhoy 4I

Do you mean the rate of a reaction is independent of the concentration of the reactant? If so, just look at the table and see if that specific reactant concentration is changed ( for example it is doubled), then you check the rate of the reaction. If the rate of the reaction did not change due to th...

Brian Chhoy 4I

It is used if one(or both) if the oxidizing(or reducing ) agents are not conductors. Thus, if they are not a metal or if they aqueous ions, before and after the reaction, you need an inert metal such at Pt, to be the electrode and transfer electrons. In the cell diagram, you would just add a vertica...

Brian Chhoy 4I

I would think that you would need to include the H+ and OH- in the cell diagrams, but I dont think water is included.

Brian Chhoy 4I

The H+ will be with the Cr207 because the h20 will be included with this half reaction to balance the oxygens, and the H+ will be needed the balance the hydrogens from the h20.

Brian Chhoy 4I

How would one figure out the oxidation numbers for certain elements in a reaction?

Brian Chhoy 4I

What is the difference between cell potential and standard cell potential?

Brian Chhoy 4I

In what situation would you know to use the nerst equation?

Brian Chhoy 4I

Oxidation occurs at the anode and reduction occurs at the cathode

Brian Chhoy 4I

The Boltzmann constants is in terms of per particle. Thus to get to the Boltzmann constants' units of J/K, you would just have to divide the gas constant (8.315 J/(mol*K)) by avagadro's number to get rid of the moles and get it into the per particle terms.

Brian Chhoy 4I

I dont think R is ever used as a C value in the entropy equation as temperature changes. The C value also changes depending on the shape od the molecule. Th R value by itself would mostly be used in the work equation for reversible work.

Brian Chhoy 4I

Also take into account the shape of the molecule because whether it is monatomic, linear, or non-linear changes the C value in both constant pressure and volume.

Brian Chhoy 4I

The 8.314 J*mol^-1 *K^-1 would be the R value that you need to calculate the w in that equation. If you need to convert units, 101.325 J= 1L*atm. Thus R also equals 0.082057 L*atm* mol^-1 *K^-1, which is the R value used In the ideal gas law.

Brian Chhoy 4I

It should let you know in the problem. If they are asking for the work done in an isothermal expansion (constant temperature), you probably have to solve for the reversible pathway, since the work the system is doing if being provided energy by some outside source, such as a heat reservoir. If the q...

Brian Chhoy 4I

Almost all real world reactions that occur are irreversible, since the change in volume happens spontaneously. A reversible reaction is purely hypothetical, since it cannot happen in the real world. However, in the case of this class, the problem will probably tell you if they want you to calculate ...

Brian Chhoy 4I

The integral equation is used when calculating reversible expansion done by a gas, since in this case it is set up so that the change in pressure occurs in small increments till it reaches the volume it should be at in equilibrium. In reversible expansion, the external and internal pressures are nea...

Brian Chhoy 4I

Heat flows from hot to cold and because the temperature of the two are now the same and will remain constant, heat will not be transferred between them

Brian Chhoy 4I

If a reaction is reversible, it just means that if either the external or the internal pressure are very close to equal and that if either of them is changed slightly, the volume of the container would change. Thus the change in pressure of the reaction is occurring in very small units as it approac...

Brian Chhoy 4I

This seems possible. You would just have to multiply the denominator out( for example (1-x)(2-x) = 2-3x+x^2). Then multiply the denominator with the K value. Last just subtract the x value from both sides to get the equation you need to plug into the quadratic equation.

Brian Chhoy 4I

Im not to sure about the exact concentration of hydronium or hydroxide, but strong acids/bases have pKa/pKb values that are greater than 10^3, and at that amount you can be sure that they fully dissociate.

Brian Chhoy 4I

Yes, in short it will cause the reaction to shift towards the side with the least amount of total molecules.

Brian Chhoy 4I

The quotient (Q), is simply the ratio of products:reactants at that point in the reaction. Eventually Q will have to approach K and thus we can make assumptions about how the reaction will proceed using the Q.

Brian Chhoy 4I

Since there are so many more weak acid/bases than there are strong ones, I would suggest memorizing the strong ones instead. Last quarter, Lavelle gave us a run through of how you can easily identify the strong acids. Additionally, most likely the question will at least give you a Kb or a Ka, and fr...

Brian Chhoy 4I

In part, yes. The less moles there are, the less molecules you have colliding with the surface of the container and thus applying less pressure. Also consider the equation PV= nRT, as the number of moles decreases, the pressure has to decrease.

Brian Chhoy 4I

I don't remember a bar graph relating Q and K. However, just keep in mind that if Q<K, the products are still being produced at the cost of the reactants in the forward reaction. and if Q>K, the products are still being used to create the reactants in the reverse reaction. The only bar graph that I ...

Brian Chhoy 4I

Recall that you solve for K=(products)/(reactants). Thus when Q<K, to increase Q and get the reaction to equilibrium, you would have to increase the numerator(products) and decrease the denominator(reactants). That is why more products are formed. The same can be said for when Q>K, to decrease Q and...

Brian Chhoy 4I

Im not too sure, but considering the fact that diatomic halogens are more stable than the products, I would assume that the reaction of the decomposition is endothermic since you would have to put additional energy into the reaction to break the bond and make it go from a stable state to a less stab...

Brian Chhoy 4I

Changing pressure would result in a change in volume and since concentration= moles/volume, the concentration of the reactants and products would change respectively. Changing temperature would cause the concentration of either the reactants or products to change depending on if the forward/reverse ...

Brian Chhoy 4I

Lewis acids are those that accept e- pairs, while Lewis bases are those that donate e- pairs. Bronsted acids donate H+ (protons) while Bronsted bases accept H+. Thus the main difference between the two is more to do with what they are focusing on during the reaction, e- pairs for Lewis and H+ for Br...

Brian Chhoy 4I

My take on the process would be to just start by drawing out the molecule from left to right. The beginning is pretty simple, with a carbon in the center bonded to 3 hydrogens and 1 carbon. The COOH part is just to show that the hydrogen is attached to the oxygen rather than to the carbon. If it wer...

Brian Chhoy 4I

The shape of the molecule with the lone pair doesn't make the molecule trigonal planar. The lone pair is still there and thus keeps the electronic shape tetrahedral, and its molecular shape trigonal pyramidal.

Brian Chhoy 4I

The lone pair still plays a role in the shape of the molecule, thus making the electronic shape tetrahedral. Just picture a tetrahedral shape with the atom at the top missing, leaving a trigonal pyramidal shape, with bond angles that are slightly less than 109.5

Brian Chhoy 4I

Its electronic shape would be that of a tetrahedral, while the molecular shape is that of trigonal pyramidal. Maybe you confused the two terms?

Brian Chhoy 4I

It has 4 regions of electron density because lone pairs count as areas of electron density as well. A double or triple bond is still considered only one region of electron density. The bond angles are less than 109.5 because lone pairs have a stronger repulsion than bonded pairs.

Brian Chhoy 4I

I would think that they have very similar bond angles, ones that are <90 degrees due to the lone pairs. However the one with 3 lone pairs might have a slightly smaller angle. Although, I dont think we would need to know the specific angles for each, just that they are less than what you would expect...

Brian Chhoy 4I

Yes, for example for if a central atom with 5 regions of electron density has 3 lone pairs, it will have a linear shape. The same can be said for a central atom with 6 regions of electron density that has 4 lone pairs.

Brian Chhoy 4I

It has access to its d orbital because it is in the 3p block, which is close enough to the 3d sub shell to use when making bonds. However, in its ground state and when it is not making any bonds, its 3d sub shell is not in use.

Brian Chhoy 4I

Yes NH3 would have a shape of trigonal pyramidal, since the lone pair doesn't count as part of the shape. However, its electronic shape (shape considering all regions of electron density) would be tetrahedral.

Brian Chhoy 4I

This measures the polarity of a bond within a molecule and is measured in coulomb-meters.

Brian Chhoy 4I

Increasing the size of an atom increases the attractive forces because it increases the dispersion forces, or the uneven distribution of electrons in the electron cloud, and thus creates more dipole and induced dipole moments.

Brian Chhoy 4I

Molecules with high polarizability boil at higher temperatures because polarizability is how easy it is to move its electron cloud. Thus those with easily movable electron clouds are more likely to have more dispersion forces, which are the uneven dispersion of electron in the electron cloud, and th...

Brian Chhoy 4I

The valence electrons for the elements in the d block are always the amount of electron in the outermost shell. For example, for Mn: [Ar] 4s^2 3d^5. There are 2 valence electrons because the 4th energy level is the outer most orbital.

Brian Chhoy 4I

The 4s orbital is written before the 3d orbital to show that it is of lower energy, since the farther the orbital you go, the more energy it has.

Brian Chhoy 4I

Both would be correct to identify the ion. If you want to show where the electrons are more specifically, you should do the entire ground state configuration, which is probably the best way to answer the question.

Brian Chhoy 4I

I would think he just meant if the car had a wavelength that was big enough to notice and detect while moving. For example, when you did the calculation for the wavelength of a car with a mass of 1.5 * 10^8 kg moving at a speed of 27 m/s, the wavelength would be 1.64 *10^-38, which is really small a...

Brian Chhoy 4I

Yes the 6s orbital would begin to fill before the 5d orbital because it has a lower energy than that of the 5d orbital. Keep in mind that lower energy orbitals always fill up before higher orbitals. If you need more clarification: https://www.chemguide.co.uk/atoms/prope ... oblem.html

Brian Chhoy 4I

It basically means that there can only be two electrons in each orbital (state). For example, when drawing an aufbau diagram, in each orbital there are only two electrons, the one that spins up and the one that spins down.

Brian Chhoy 4I

It plays into the fact that we are only talking about a particle with very little mass, such as that of an electron. When trying to measure the speed of a particle passing by we would count how long it takes to move from one position to another. However, when you do so you are messing up the origina...

Brian Chhoy 4I

You should use the smaller n value as the n1 value and the bigger one as the n2, because the n1 should be the initial state.

Brian Chhoy 4I

Its B. You know that an electron going from 5 to 1 would emit more energy than that from 4 to 2, since the energy emitted is proportional to the distance the electron falls. Energy is also inversely proportional to wavelength, with higher energy having smaller wavelengths. If you would want to see t...

Brian Chhoy 4I

keep in mind that v= velocity, and that $\nu$ = frequency(curly v). But yes in that case v is velocity

Brian Chhoy 4I

Right, id think the amount of electrons would play a role in the energy of the electron due to the repulsion. I would also think then that the element plays a role due to the amount of protons and neutrons, which keep the atom together and thus change the amount of energy needed to excite the electr...

Brian Chhoy 4I

I think the equation for E=hc is only for light, so even though an electron has both waves and photon like properties, you won't get the same answer as if you used the de Broglie equation which is for particles.

Brian Chhoy 4I

The question states that "protons and neutrons have nearly the same mass. How different are their wavelengths? Calculate the wavelength of each particle when traveling at 2.75 * 10^5 m/s in a particle accelerator and report the difference as a percentage of the wavelength of the neutron." ...

Brian Chhoy 4I

I would assume so, since some of the homework problems include those types of questions. Just remember that visible light is between 400 to 700 nm, infrared is between 700 to 1000 nm, UV is 10 to 400 nm, and gamma rays are anything smaller than that. You could memorize the frequencies if you'd like,...

Brian Chhoy 4I

Hi,
I've seen some questions where they list the energy of the photon in keV. Is this similar to an electron volt (eV)? and how would you convert this to joules?

Brian Chhoy 4I

This is a combustion analysis question. I would start the question to trying to find the exact masses of carbon, hydrogen, nitrogen, and possibly oxygen too. Take the mass of each product and convert it to mass to the exact mass of that element produced. For example, with the carbon dioxide, divide ...

Brian Chhoy 4I

The way I would approach this problem would to at first convert the mass of sodium carbonate to moles of the compound, and then divide this by .25 L to get the molarity of the solution (0.0796 M). Now for each question that they are asking for, start by converting the mmoles to moles by dividing by ...

Brian Chhoy 4I

The post above is correct, but there are multiple ways to approach these types of problems. The method I usually use is to take to given masses of the reactants and convert them to moles of reactants. Followed by using the mole ratio and converting that to the total moles of the product that can be ...

Brian Chhoy 4I

The question states that the molar mass of the metal hydroxide M(OH)2 is 74.10 g/mol and asks to calculate the molar mass of the sulfide of the metal. I'm assuming that the M is a variable for a certain metal with a +2 charge. Is the question simply asking for the molar mass of MS, by subtracting th...

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