CHEMISTRY COMMUNITY

Harry Zhang 1B

Oxygen here is the reactant and therefore its final-initial will be a negative value and the negative sign you see in the unique rate formula takes care of that negative sign and change the rate into a positive one. For the reason of comparing, all rates are considered to be positive in this type of...

Harry Zhang 1B

Since the pka is lower than the ph given, the acetic acid will act as an acid and will partially dissociate into H3o+ and CH3COO^-. Therefore, its net charge is -1.

Harry Zhang 1B

It's independent if changing its concentration does not affect the rate of the reaction.

Harry Zhang 1B

For this question, since specific heat is an extensive property, a smaller volume of water will have a lower specific heat and have a larger increase in temperature. This option is also the most concentrated.

Harry Zhang 1B

If the problem does not specify whether the reaction happens in the excess of reactants, you should always consider the possibility of limiting reactants.

Harry Zhang 1B

It will be included in the equilibrium expression. The only things not included will be elements in the state of solid or liquid.

Harry Zhang 1B

You should use appendix 2 to find the half-reactions happening in cathode and anode. Remember, cathode is the one with a higher E. Then balance the half-reactions and write them out to determine Q. Faraday's constant was not used because it was included in the formula given in the book after multipl...

Harry Zhang 1B

Look at whether it's spontaneous(thermodynamics) and whether the reaction occurs at a fast rate(kinetics).

Harry Zhang 1B

You might have used the wrong units. The G given in the appendix is in kJ but if you are using 8.314 as your R, convert kJ to J. Your standard G is wrong. You should check your calculations and see if you still have that number. I got 91.12 kJ/mol and this will give the answer in the solutions manua...

Harry Zhang 1B

In balancing half reactions, the first step is always to balance the number of oxygen atoms by adding H2O. The next step is to balance the H atoms, and this is what's different. In an acidic solution, after you balance the O atoms, you will balance the H atoms by adding H+ on the side that needs it,...

Harry Zhang 1B

Write out the half reactions and balance them will help you find the number of electrons transferred in the process and hence n in the formula.

Harry Zhang 1B

The anode is always on the left and the cathode is always on the right. You can also verify this by writing out the half reactions and see where oxidation and reduction happen.

Harry Zhang 1B

Cathode is where reduction happens and anode is where oxidation happens.

Harry Zhang 1B

Oxidizing agent is the element that does the oxidation(taking away electrons from another element, and therefore the oxidizing agent is reduced). Oxidation is when electrons are lost, which represents the element that the oxidizing agent is acting upon.

Harry Zhang 1B

Temperature is not a condition of standard state but 298 K is usually used when standard state values are given. Temperature can be any value in a standard state condition. If the question is in STP(standard temperature and pressure), the temperature is 273k, but this is different from standard state.

Harry Zhang 1B

Adding an inert gas will not have effect on the system because the inert gas does not participate in the actual chemical reaction and does not change the partial pressure or the volume(therefore concentration) of the reactants and products.

Harry Zhang 1B

If it's merely change in temperature, yes, because the conversion to K by adding 273.15 will cancel out. However, if you are using it like 1/T2-1/T1, then you will have to convert it.

Harry Zhang 1B

Delta G is zero when an equation is at equilibrium because it has no tendency to shift to the reactant or product side but rather just stay as it is.

Harry Zhang 1B

This is so because bond enthalpy measures the change in energy when breaking bonds. On the reactant side, bonds are broken but on the product side bonds are formed; therefore, we use reactants-products to give the bond enthalpy on the product side a negative sign, which makes sense because forming b...

Harry Zhang 1B

In an isothermal process, the average kinetic energy of the molecules stay the same and since there is no force between the molecules, the potential energy also stays the same. Therefore, delta U=0.

Harry Zhang 1B

at constant pressure, delta H=q=765 J. The molar heat capacity of a monatomic ideal gas at constant pressure is 5/2 R, which is 20.785J/kmol. To calculate temperature change, use q/(C*the number of mols of Kr), which is equal to 44.89K. The final temp at constant pressure is therefore 343K. At const...

Harry Zhang 1B

Since entropy is a state function, to calculate the entropy of vaporization of water, you can use the equation: entropy change of heating the water from 85 to 100+entropy change of vaporizing the water at 100(constant temp.)+entropy change of cooling the vapor from 100 to 85. 75.3*ln[(100+273)/(85+2...

Harry Zhang 1B

1 mol of atoms bound into diatomic molecules means there are 0.5 mol of diatomic molecules(1 mol*(1 mol molecule/2 mol atoms). This means the entropy of this will be lower than that of 1 mol of atoms because there are more single atoms and hence greater disorderliness.

Harry Zhang 1B

Extensive property depends on the amount of the substance. Heat capacity is an extensive property because if you have 1000L water, it will have a high heat capacity(rise slower in temperature) than 1L of water. Specific heat capacity is not an extensive property because the unit is typically in J*De...

Harry Zhang 1B

Yes, buy you are missing a T in your equation. The equation should be -nRTln(V2/V1)=Work of system.

Harry Zhang 1B

The change of internal energy of a system is zero in isothermal expansion. This formula is related to the equipartition theory and can be used to calculate the internal energy of molecules or atoms by taking into account rotational and translational energy.

Harry Zhang 1B

Degeneracy is a measure of the number of ways molecules or compounds can be arranged in the same total energy. This is is related to the idea of entropy because it takes into account the number of microstates possible, which all contribute to the disorderliness or randomness of a system(spontaneity)...

Harry Zhang 1B

The first one is used when the specific heat is given in terms of J/K/mol(molar specific heat).

Harry Zhang 1B

Reversible expansion means when the expansion can be reversed by an infinitesimal change, while irreversible means when an infinitesimal change will not reverse the direction of expansion.

Harry Zhang 1B

You would use 1L*atm=101.325J. This can be found in a example problem on page 247.

Harry Zhang 1B

Work done by a system is when a system does work on the surrounding, such as gas pushing out the piston and expand its volume. This will result in a negative W value because the system LOSES ability to do work now that it can no longer push on the piston because the pressure under the piston and the...

Harry Zhang 1B

Since enthalpy is a state function and sublimation means the subject goes from a solid to a gas, the enthalpy of sublimation=heat involved in fusion+heat involved in vaporization

Harry Zhang 1B

The calorimeter often consists of the container and a solvent(typically water). The system refers to the chemical reaction happening right inside the solution, and the surroundings would be the solvent(the water) and the container.

Harry Zhang 1B

When a reaction has reached equilibrium, it means that the forward and reverse rate of the chemical reaction is the same and therefore there is no change in the concentration of products and reactants even though the system is still active.

Harry Zhang 1B

Since the solvent here is water, there will be H3O+ due to the autoprotolysis of water.

Harry Zhang 1B

In pH value, only the numbers after the decimal point count as sig.figs., so you need to write as many numbers after the decimal point as there are in the number of sig.figs. in the question.

Harry Zhang 1B

Pressure only affect the equilibrium concentration if there is a change in volume since a change in volume will affect the concentration of the molecules involved in the chemical reaction because of the formula Concentration=n/V. Increasing pressure by adding inert gas will not affect the volume and...

Harry Zhang 1B

All the conjugate base/acid of a strong acid or base will not affect the pH of the solution because they are the extremely weak conjugate base and acid of strong acid and base and therefore will not play a role in changing the pH level.

Harry Zhang 1B

This is asking how will a reaction shift if we start with more reactants. You can think of it as the reaction quotient Q. If we start with more reactants, Q will be smaller than k and therefore the reaction will shift to the right to produce more products.

Harry Zhang 1B

Yes. The system will try to minimize the decrease in reactants by making the reaction to shift to the left and create more reactants when some are lost.

Harry Zhang 1B

The chemical reaction is an endothermic reaction because it's breaking the bond of one molecule to separate it into two molecules. Therefore, increasing the temperature will lead the reaction to shift to the product side.

Harry Zhang 1B

If you are given enough information to calculate the molar concentration of all of the species in the reaction, you can use Kc even if the species are all in gaseous state. Sometimes the question only gives partial pressures, which means you can only use Kp in that case.

Harry Zhang 1B

Water is amphiprotic and can thus act as both a proton donor and a proton acceptor. Therefore, when there are two water molecules, one of them loses a proton(H+) and the other accepts it, resulting in a H3O+ and a OH- molecule.

Harry Zhang 1B

First, calculate the molar concentration of H2 and I2 in the flask, which is n/v. From there, since the question says that 60% of the hydrogen gas reacted at equilibrium, it means that to reach equilibrium, H2 reduced by 0.6 of its original concentration. Therefore you will multiply 0.6 by the molar...

Harry Zhang 1B

Yes. The formula for calculating both equilibrium constant is the same and the underlying concept is also the same: the equilibrium constant is the same under the same temperature despite changes made to partial pressures or concentrations.

Harry Zhang 1B

They are not included because they are not dissolved and hence their concentration is constant or cannot be calculated. Even if you put some more pure solid or some more pure liquid into the solution, you are just increasing the amount of such solid or liquid but their concentration does not change.

Harry Zhang 1B

The reverse reaction will begin when Q is larger than K, because in order for Q to approach K, it needs to get smaller, and the only way to do that is to make the denominator of the Q expression, or the concentration of reactants, higher.

Harry Zhang 1B

You can determine the direction that a reaction goes to by looking at the Q and K value. If the Q value is smaller than the K value, then in order for the reaction to reach K, or equilibrium, there needs to be more products, and if the Q is larger than the K value, there needs to be more reactants f...

Harry Zhang 1B

You use Q when the reaction is not in equilibrium and you use K when the reaction is in equilibrium.

Harry Zhang 1B

This is because NH4I will dissociate in water and the definition of a bronsted acid is a proton donor and NH4+, being a strong conjugate acid of a weak base NH3, will donate its proton to the water molecule. On the other hand, I- is the weak conjugate base of a strong acid HI and will not affect the...

Harry Zhang 1B

The definition of bronstead acid/base is that it is a proton donor/acceptor. Looking at NH3, the hydrogen atoms bound to the nitrogen are not likely to fall off and bind to another atom since NH bonds are not polar enough to give the hydrogen a sufficiently positive charge to allow it to bind to an ...

Harry Zhang 1B

A chelating ligand is a special type of ligand that binds to the central transitional metal at more than one site, forming a ring-like structure. Chelates are especially important in biological systems(Cisplatin can prevent DNA replication; myoglobin carries oxygen...). This relates to a ligand bein...

Harry Zhang 1B

We must input the concentration(mol*L^-1) when using the -log formula to calculate pH level, therefore, you will need to divide the result you got from your first calculation by 0.250L and then input the result into -log to calculate the pH level.

Harry Zhang 1B

The chemical equation is not balanced(The I2 should be just I^-(aq)). After correcting this, writing the net ionic equation, the I^- ions will cancel out and the species left are NH4+,H2O,H3O^+,NH3. Since the proton donator is NH4+, NH4+ is the bronsted acid.

Harry Zhang 1B

Although there are two lone pairs of atoms on the oxygen atom, it can use only one of those pairs to bind to a transitional metal and the other pair would then not be in the correct geometry to bind to the transition metal on a different site.

Harry Zhang 1B

Just like how vectors can only cancel out each other when they are opposite to each other, you can draw out the dipole moment in a molecule and see if they cancel, but you must solve this by using the VSEPR model instead of the lewis structure since the VSEPR gives a more accurate 3D shape. A specia...

Harry Zhang 1B

Hydrogen bonding happens when and H attached to N,O, or F is bonded to the N,O,F on the other molecule. Therefore, whenever a N, O, or F atom has a lone pair of electrons, it can be bonding site.

Harry Zhang 1B

Ionic bond is the strongest bond and therefore KCl and KI will have higher boiling points than H2S and H2O. Between KCl and KI, because the iodine atom is larger than Cl and is more polarizable, the bonds between KCl formula units have some covalent character and is therefore weaker than KCl. Betwee...

Harry Zhang 1B

The repulsive force between electrons is ranked as, lone-pair-lone-pair>lone-pair-electrons and electrons in a bond>electrons in a bond and electrons in the other bond. Therefore, lone pairs of electrons around the central atoms will be arranged in such a way they are furtherest from each other and ...

Harry Zhang 1B

VSEPR gives the 3d shape and the bond angles within a molecule and is able to give us information in terms of the molecule's polarity and how lone pairs repulse each other, which cannot be given by simply looking at the lewis structure.

Harry Zhang 1B

You can determine the dipole moment by comparing the difference in electronegativity; the atom with a higher electronegativity is partially negative and the atom with a lower electronegativity is partially positive since its electrons are more attracted toward the other atom.

Harry Zhang 1B

All molecules have london dispersion forces because it is experimentally observed that the electron clouds in molecules are not fixed and tend to move around, which results in temporary dipole moments that create the london dispersion forces in neighboring molecules.

Harry Zhang 1B

It is tetrahedral about the carbon atom but it is linear about the Be atom.

Harry Zhang 1B

The lewis structures look the same because you can only draw them in a two-dimensional space but the VSEPR model depicts the shape in a three-dimensional space and illustrates the effect of repulsion by a lone pair, which results in a different shape and is not trigonal planar(has no lone pair).

Harry Zhang 1B

The angles can only be determined experimentally but if there is no lone pair, each type of VSEPR structure has specific angles in between the bonds. To do this, you can only memorize the angles for more complex shapes such as tetrahedral... But for other shapes such as linear, the angles have to ad...

Harry Zhang 1B

It is polar if there is a difference in electronegativity since electrons are more pulled toward the one with the higher electronegativity, creating a charge.

Harry Zhang 1B

Electron affinity is the energy difference between a ground state atom and after the atom gets an electron. Electronegativity is the tendency or an atom to attract electrons. These two terms have the same trend on the periodic table, but electronegativity can be seen as taking an average of both ion...

Harry Zhang 1B

Hydrogen bonding is another way of saying there is a strong dipole-dipole attraction between two molecules, but because the electronegativity between these atoms are larger than a normal dipole moment, we call them hydrogen bonding, which is the strongest intermolecular force.

Harry Zhang 1B

Temporary dipole is when a molecule is not actually polar but because of the shifting electron clouds it creates a temporary dipole moment. Permanent dipole is formed when the difference electronegativity is large enough to allow the electronegative atom to constantly attract electrons from the othe...

Harry Zhang 1B

All molecules have london dispersion forces because the electron clouds in a molecule is nit fixed and tend to shift around and give the molecule an instantaneous dipole moment that allow bonds to be formed in between. They are the weakest because these dipole moments are weak, unstable, and tempora...

Harry Zhang 1B

Covalent bonds can have increasing ionic character if there is a difference in the electronegativity between the two elements , which there always is between two different element. The larger the electronegativity, the larger difference in their ability to pull electrons to itself, which then become...

Harry Zhang 1B

If the covalent bond is between two different element then yes it is polar because having a dipole moment means the electrons are not equally shared and there is a difference between any two different element, large or small.

Harry Zhang 1B

The 3d orbital will never be filled before the 4s orbital because any (n+1)s orbital is lower in energy than the nd orbital if there is no electron in the 3d orbital. However, after the 4s is filled and there is one electron in the 3d orbital, you would move the 3d orbital to the left of the 4s orbi...

Harry Zhang 1B

For example, if you are drawing the ionic compound NaCl, Na will have no dots around it because it lost its valence electron indicated by the +1 charge and chlorine will have 8 dots around it because it pulled the electron from Na to itself, indicated by the charge 1-. Then you would draw them separ...

Harry Zhang 1B

The highest energy level is told to be zero because this is the point where the electron is completely removed from the atom and no longer experiences any pull force from the atom. You can see this as an energy level that takes an infinitely large number such as 1*10^999, which if you insert it into...

Harry Zhang 1B

Lone pair electrons are just electrons that are not shared with another atom therefore just count the electrons that are not in between two atoms but instead only on the side of ONE atom.

Harry Zhang 1B

Delocalised electrons means that in a resonance structure, the electrons are not particularly associated with specific atoms in one specific location, they are instead conceptually distributed over various pairs of atoms and cannot be drawn with a stationary, one-dimensional Lewis structure since in...

Harry Zhang 1B

To do this type of problem, you only need to know what makes an atom stable(full s and p orbital or lower energy) and know which atoms are metal(lose electrons) or nonmetal(gain electrons).

Harry Zhang 1B

The expanded octet concept comes from the idea that normally we would consider the valence orbitals of an atom or the outermost shell of an atom can hold no more than 8 electrons. An expanded octet is then an atom that holds more than eight electrons in its outmost shell. Atoms in or after period 3 ...

Harry Zhang 1B

First you will need to determine how many valence electrons there are in each atom by looking at the periodic chart(their group number), which is more efficient than writing out its electron configuration to determine. Then you will need to arrange the electrons around the atoms in a clockwise manne...

Harry Zhang 1B

This tells you where the electron is (the orientation of the orbital in regard to the three axes, x, y and z)after knowing the location of the shell and shape of the sub shell. For example, 2p gives you the first two quantum number but to know which orbital of the three orbitals in p subshell the el...

Harry Zhang 1B

It states that no more than two electrons can exist in the same orbital and that if they do they have opposite spins. This is because of the property of electrons(the exact property is too complicated) in the quantum world makes them impossible to have the exact quantum state(same n, l, ml, ms). The...

Harry Zhang 1B

Normally, the order of electron-filling takes the following sequence: 1s 2s 2p 3s 3p 4s 3d.... However, when the electrons contain more than 20 electrons, that is, after potassium starting with scandium, the 4s orbital is complete and electrons start going into the 3d orbital but once there is elect...

Harry Zhang 1B

It is a value or description of the electron from a quantum view. The spin of an electron is mainly determined by another electron that interacts with it and in the case of an electron in the atom, it would be arranged in a way so that it has the lowest energy possible. That being said, if an electr...

Harry Zhang 1B

This is so because Neon belongs to what we call the noble gas family in the periodic table(last column) and all the atoms in this family has the same electron configuration in which there is no unpaired electron and a full s and p orbital, which makes them extremely unstable and therefore unreactive.

Harry Zhang 1B

The De Broglie equation can be used with any object as long as you have the p=momentum of the object, therefore theoretically you can also use it with light because although photons don't have mass, they still have momentum, but in order to this you have to be given its momentum since you cannot cal...

Harry Zhang 1B

The reason why we say light has both wave and particle properties is because it's experimentally proven. The diffraction patterns that shows up when certain wavelength of light passes through a crystal confirms its wave-like property. When conducting the photoelectric experiment, we notice that if t...

Harry Zhang 1B

It makes sense to group them in this way because as you already saw during Dr. Lavelle's lecture, the energy difference between n=1 and any other level is the largest while the energy difference between n=2 and any other level is relatively smaller. This is the reason why a gap is observed on the em...

Harry Zhang 1B

When you see this kind of problem, the first thing to do is to just calculate the molarity of the original solution. Since the question is asking how much volume is needed to obtain a certain amount of moles of sodium carbonate, the logic here would be what volume of the original solution would cont...

Harry Zhang 1B

It has 3 significant figures because when looking at significant figures in scientific notation, we only look at number on the left side, and since 7.00 has a decimal point, it has 3 significant figures. Another way to look at this is that this number is accurate to the hundredth place, so even if y...

Harry Zhang 1B

Yes, it will be fine as long as you have the correct number of sig. fig. in your expression. An exception to this would be if the question explicitly asks you to express your answers in specific units.

Harry Zhang 1B

Things that are constant such as molar masses should not be taken into consideration for sig. fig.. We normally determine the number of sig.fig. by looking at the number given by the question that has the least number of sig. fig..

Harry Zhang 1B

The theoretical yield can be directly calculated by the number of moles of reactants given in the problem(or obtained from the grams used). You would use the mole-to-mole ratio in a balanced chemical equation to find out how many moles of products are produced and convert it into grams. This is call...

Harry Zhang 1B

This is not always the case, you would want to write a new equation without putting any stoichiometric coefficients that you got from the first equation because these stoichiometric coefficients are unique relative mole numbers in chemical equations. The moles of products you got from the first equa...

Harry Zhang 1B

One thing to keep in mind is that the moles of solute never change. So to find out how many moles of solute are in the solution, we multiply 0.2 M by 1.0, which indicates that there are 0.2 moles of ammonium nitrate molecules. In this case, you final volume would be 1 L + 3 L, Which equals to 4 L. D...

Harry Zhang 1B

Imagining you have a cup of water with five red beans in it. The solute is the red beans and the solvent is the water. To dilute this solution, we add water to the cup, however, the number of red beans remain unchanged and therefore the number of moles of solute remains unchanged; in this case, it's...

Harry Zhang 1B

There is a formula for figuring out how to write the name of certain chemical compounds. In order to do this, we need to first put different chemical compounds into different categories. Binary compounds can be divided in to three categories, binary ionic compound, binary covalent compound, and bina...

Harry Zhang 1B

Your previous steps are correct, so I will just answer what to do next. After getting the number of moles of each reactant, you should use stoichiometry to determine the number of moles of either one of the product produced. Let's say we choose NO(g) as the product that we will be using to compare t...

Harry Zhang 1B

In order to find the number to multiply on a empirical formula to figure out the molecular formula, you must be given the molar mass of the compound and then divide it by the mass of the empirical formula you obtain to see the proportional relationship between them. If you get a number of 2, simply ...

Harry Zhang 1B

The reason that you need to multiply Na^+ by 2 is because in one molecule of Na2CO3, there are two Na^+ ions(which balances the negative 2 charge that CO3^2- ions carry), and so the number of sodium ions will always be 2X more than the number of Na2CO3, which means its molarity will also be 2X more ...

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