CHEMISTRY COMMUNITY

Tyler Angtuaco 1G

For a three step reaction, is there a way to determine which of the fast steps has the higher activation energy if we are not provided these values? Question 7.11 only provides us with three sets of reactions (which we have to assume which one is slow and which are fast based on the overall rate law...

Tyler Angtuaco 1G

Raising the temperature for endothermic reactions will make the production of products more favorable (forward reaction). Conversely, raising the temperature for exothermic reactions makes the production of products less favorable (forward reaction). As for temperature's effect on rate constants, yo...

Tyler Angtuaco 1G

You can infer order based on stoichiometric coefficients only during the individual steps of a reaction. You cannot for the overall reaction. For the overall reaction, you would need experimental data and use the method of initial rates.

Tyler Angtuaco 1G

The Arrhenius equation can be re-written as ln k = -Ea/RT + ln A if you take its natural log. In this new form, you can compare the rate constants at two different temperatures using the equation you listed since subtracting lnk of one temperature and lnk of another cancels the term lnA.

Tyler Angtuaco 1G

They are the same as order for individual steps of a reaction, but not the overall reaction.

Tyler Angtuaco 1G

The slow step is denoted in the problem. It is also the step whose rate matches the overall rate law.

Tyler Angtuaco 1G

Typically, you'll need to determine the oxidation and reduction half reactions. In each half reaction, balance all elements aside from H and O. Next, balance oxygens with water, then hydrogens with H+ ions. If the solution is alkaline/basic, balance H+ ions with OH- ions and combine them as water. T...

Tyler Angtuaco 1G

Both are fine since they are inert and allow the redox reactions to occur.

Tyler Angtuaco 1G

Reducing the concentration of the reactant results in a higher Q value. Based on the Nernst equation, this would result in a lower cell potential.

Tyler Angtuaco 1G

Q is non-equilibrium ratio of products to reactants. So, you'll need to identify which species are the products and which ones are the reactants in the overall cell reaction.

Tyler Angtuaco 1G

Yes it's fine to have different units as long as they cancel out. I think you would need to convert if you had a situation where three species were given in mol L^-1 and one given in bar.

Tyler Angtuaco 1G

Question 5.55 part b reads, "A sample of graphite of mass 5.20 kg and 125 g of water were placed into a 10.0-L container and heated to 900 K. What are the equilibrium concentrations?" (In part a, we found the equilibrium constant using the equation delta g naught = -RT*lnK). The solutions ...

Tyler Angtuaco 1G

I think the statement about the necessity for an inert electrode refers to situations when the original species is in the same solution as its oxidized or reduced form. That is because I2 cannot be the anode since I- ions are already producing it in the process of oxidation.

Tyler Angtuaco 1G

I assumed that Ni2+ ions would be reduced since it was present as an aqueous solution and not solid. I also considered the possibility of the SO4 2- ion to reduce, but I realized that the reduction reaction present in Appendix 2B mentions H2SO3 as a product, which is not mentioned in the question so...

Tyler Angtuaco 1G

Yes, you can use the equation ∆G = ∆G° + RT ln Q since K is given. If K is not given, delta G naught or the equilibrium concentrations/pressures likely will be.

Tyler Angtuaco 1G

Bot equations should work since the equation using log Q is derived from the equation with ln Q.

Tyler Angtuaco 1G

Since HCl is a strong acid and is aqueous, you can imagine most if not all of the ions in the solution to be present as H+ and Cl- ions. Thus, you are analyzing the reduction of Cl2 to these Cl- ions and the oxidation of H2 into these H+ ions.

Tyler Angtuaco 1G

Your calculation should be correct based on the values given on Appendix 2B. I'm not sure either how they got -1.29V.

Tyler Angtuaco 1G

No, the order of those two ions is not important.

Tyler Angtuaco 1G

If you are referring the to the max cell potential, it is simply represented by E. This can be calculated using -work/charge or delta G = -nFE (or work = -nFE), where work is the max work that can be done from the transfer of charge.

Tyler Angtuaco 1G

The negative ions of the salt balance the increasingly positive solution of the anode and the positive ions of the salt balance the increasingly negative solution of the cathode.

Tyler Angtuaco 1G

Experiments on redox reactions usually involve the components presented in the picture you uploaded: two electrodes connected by a circuit and a salt bridge. The electrode on the left is usually the anode (electrode that includes the species being oxidized/losing electrons) and the electrode on the ...

Tyler Angtuaco 1G

Delta G naught is an intensive property (values are calculated at standard conditions), whereas delta G isn't. Using delta G naught helps observe a reaction in unstandard conditions.

Tyler Angtuaco 1G

We only need to know the application of it: observing how the equilibrium constant for a reaction is affected by temperature.

Tyler Angtuaco 1G

It helps us observe how the equilibrium ratio between products and reactants differs for a reaction conducted at different temperatures.

Tyler Angtuaco 1G

You'll use the van't hoff equation when you're observing a reaction conducted at two different temperatures and their respective equilibrium constants.

Tyler Angtuaco 1G

Yes since a spontaneous reaction is one that will likely occur on its own without intervention. Thus, products will likely form since the reaction is likely to proceed.

Tyler Angtuaco 1G

A salt solution would just be a salt plus water. The method to find pH would vary depending on what's given to you. But, you know that buffer solutions are created from a weak acid and its salt, which gives you more clues about a given reaction. Sometimes, you'll also be given Ka or Kb, which you ca...

Tyler Angtuaco 1G

It allows us to observe the relationship between the equilibrium constant and temperature.

Tyler Angtuaco 1G

If you are referring to S = kB*ln(W), it is used to calculate residual entropy.

Tyler Angtuaco 1G

I would guess the 8.314 J·K-1·mol-1 since enthalpy is in joules and temperature is in kelvin. The units would then cancel, which makes sense because the equilibrium constant has no units.

Tyler Angtuaco 1G

The v and p just indicate that it is specific heat at a constant volume or constant pressure. I can't think of a situation where you would need to convert between the two or be extra wary which one the table is giving you. Usually, if you need specific heat, just refer to what the table gives you. Y...

Tyler Angtuaco 1G

Question 4D 15 lists values I assumed was heat of formation, but labels them H with subscript c. What does this symbol mean and is it correct to assume it means the same as heat of formation?

Tyler Angtuaco 1G

Why is it safe to assume that delta H = heat (delta H = q) for chemical reactions even if the question does not specify that pressure is constant?

Tyler Angtuaco 1G

If you are given the heat of reaction in kJ but want to express it in terms of a reactant or product, is it correct to write "kJ per mole of said reactant or product?" Or is this an invalid statement?

Tyler Angtuaco 1G

The enthalpy of reaction is -13168 kJ per mole. The solutions manual divides this value by four (using stoichiometric ratios) to put this in terms of TNT, whose enthalpy density is what we are trying to find. If we are just using stoichiometric ratios to find this value in terms of TNT, why do we co...

Tyler Angtuaco 1G

Yes, just add the heat supplied to the copper kettle and the heat supplied to the water to find part a. For part b, divide the heat that is supplied to the water by the total heat supplied to the system.

Tyler Angtuaco 1G

It's most helpful to consider what reversible and irreversible expansion is in the context of a system with a piston. Reversible expansion: If the external pressure and pressure of the system are pretty much equal, a slight increase in external pressure would cause the piston to move slightly in due...

Tyler Angtuaco 1G

Would a strong acid or strong base in gas form fully dissociate in the presence of water in gas form?

Tyler Angtuaco 1G

The second equation is likely referring to the work done on the system, which is why it is positive. The first one you mention is what will be used most for the problems in the thermodynamics section since our observations are typically made in reference to the system and the work it is doing.

Tyler Angtuaco 1G

The table for specific heat is provided earlier in the chapter.

Tyler Angtuaco 1G

We wouldn't need n or m if we were only attempting to find the heat capacity of a substance in general. We would need it, however, if we were curious about the (specific) heat capacity of a sample of this substance.

Tyler Angtuaco 1G

The final temperature of the system is less than the initial temperature of the system since the exothermic reaction caused the release of heat.

Tyler Angtuaco 1G

I think this refers to the moment when a sample is about to change states of matter. If you observe a heat curve, you notice that when ice is melting into water or water is freezing into ice, temperature remains constant regardless of how much heat is added or lost. This is because the sample is abs...

Tyler Angtuaco 1G

Probably only when your adding reactions that don't involve common molecules or elements, such as if one molecule or element is present in one reaction but not the other(s). This is likely the case since heat of formation will be different with molecules or elements of different bond energies. I don...

Tyler Angtuaco 1G

You use the heat/enthalpy of vaporization since the reactant is being vaporized into gas. You use bond enthalpy since the bond in the diatomic molecule Br2 breaks, forming two bromine atoms in the reaction.

Tyler Angtuaco 1G

Work is applicable to everything, but not everything in this course requires you to calculate it. A good majority of thermochemistry will revolve around enthalpy, change in enthalpy, and other concepts of energy change. You won't need to calculate work with the formula force times distance.

Tyler Angtuaco 1G

Bond enthalpy refers to the energy it takes to break a bond in any particular molecule, whereas standard enthalpy of formation is the enthalpy change produced from the formation of a product from its reactants. Keep in mind the standard enthalpy of formation is the enthalpy change for one mole of a ...

Tyler Angtuaco 1G

If you are given the initial concentration of one of two reactants in a reaction, is the only reason why we cannot use molar ratios to determine the initial concentration of the other reactant because of the possibility that one of them is a limiting reactant? Or are there more reasons to this?

Tyler Angtuaco 1G

In a chemical reaction involving two reactants and two products, is it possible to assume the equilibrium concentrations of all molecules in the reaction based solely on stoichiometric ratios if only the equilibrium concentration of one product is given and if you know there was a perfect amount of ...

Tyler Angtuaco 1G

If given a balanced chemical reaction which produced two products, can you determine the equilibrium concentration of one product solely based on molar ratios if you are given the equilibrium concentration of the other product?

Tyler Angtuaco 1G

I would assume that the pressure given is the initial pressure for HCl since the question does not explicitly state it is an equilibrium value, and also because the question seems to phrase it as if it just added HCl until there was enough for the desired reaction to occur. Next, I would construct a...

Tyler Angtuaco 1G

If none of the equilibrium values are provided, use an ICE table to determine the equilibrium composition of a reaction. If one or more of the equilibrium values are provided, you can use stoichiometric ratios to determine the amount of change the initial amount of reactants or products experiences ...

Tyler Angtuaco 1G

If the question does not state the values are at equilibrium, they are not. ICE tables are needed when the equilibrium values are not provided, but are not necessary if you know the equilibrium amount of one of the reactants or products. This is because you can use the stoichiometric ratios of the b...

Tyler Angtuaco 1G

Pressure happens to be one of the parameters that affects the rate of reactions. When pressure is altered, the reaction will proceed to the side with less moles of gas. This observation can be derived by first considering the inverse relationship between pressure and volume (which affects concentrat...

Tyler Angtuaco 1G

This was in reference to the ionization constant for water, Kw, because the addition of both reactions in the example (the addition of water to ammonium and the addition of water to ammonia) resulted in the concentration of hydronium ions multiplied by the concentration of hydroxide ions (derived fr...

Tyler Angtuaco 1G

What are we expected to know about ATP hydrolysis and osmotic pressure? These are listed on the chemical equilibrium outline, but I don't remember these being discussed in lecture.

Tyler Angtuaco 1G

Are there certain units of pressure that need to be converted in order to use partial pressure values when calculating the equilibrium constant? Certainly, the equilibrium constant would be different if we were to use kilopascals instead of atmospheric pressure.

Tyler Angtuaco 1G

How will the reaction change if it is exothermic and heat is added (considering the fact that exothermic reactions release heat)? Conversely, how would it change if the reaction was endothermic and cooled (considering that endothermic reactions absorb heat)?

Tyler Angtuaco 1G

Dr. Lavelle established that increasing the pressure by decreasing volume results in the production of more products if there is more moles of gas on reactant side and more reactants if there are more moles of gas on product side. Will these trends be the same if we decrease pressure, such as if we ...

Tyler Angtuaco 1G

Just a speculation, but I would assume temperature affects the rate at which a reaction occurs, causing the equilibrium values of products and reactants to be different. This is because the temperature affects the viability of a reaction in the first place and thus the amount of products formed/reac...

Tyler Angtuaco 1G

It should not matter unless the question is asked in a way where only pressure or concentration is calculable. However, if either are acceptable, it is best to use pressure if the states of matter are all gas, and concentration if they are all aqueous.

Tyler Angtuaco 1G

Is the required number of responses for Chemistry Community still 5 responses for Chem14B?

Tyler Angtuaco 1G

A higher initial amount of reactant would produce more product. The equilibrium values of the reactant and product will also be higher and the numerator and denominator of the equilibrium constant ratio will be proportional to those of a reaction with less reactant if both reactions occur under the ...

Tyler Angtuaco 1G

Kc is always the ratio of the equilibrium concentrations of the products to the reactants, so it would just be 1/(concentration of that reactant).

Tyler Angtuaco 1G

When the equilibrium concentrations or pressures are not given, we need to calculate Q to determine whether the forward or reverse reaction is favored.

Tyler Angtuaco 1G

Q itself is just a calculation made from the current concentrations or pressures of products and reactants during some point of the reaction. Thus, it does not impact the speed of the reaction. However, you can make observations about the direction a reaction will proceed based on the comparison bet...

Tyler Angtuaco 1G

Will the value of the equilibrium constant be the same regardless if we calculate it using the equilibrium concentrations or the equilibrium pressures?

Tyler Angtuaco 1G

Is it safe to assume that the speed of a proton is the same as the speed of light?

Tyler Angtuaco 1G

How do we determine if a solution is acidic or basic if the strong base and strong acid have different concentrations?

Tyler Angtuaco 1G

What is the chemical significance of the acetate functional group?

Tyler Angtuaco 1G

How do manganese, nickel, copper, and zinc aid enzyme function?

Tyler Angtuaco 1G

What results from the addition of a weak acid and weak base? Could a salt even be formed?

Tyler Angtuaco 1G

Can someone describe the difference between hemoglobin and myoglobin in terms of their chemical structures or chemical properties?

Tyler Angtuaco 1G

It can be, such as when the concentration of hydronium is greater than one, but is uncommon.

Tyler Angtuaco 1G

Sigma bonds are the first bonds that form between atoms. Every consecutive bond (double, triple, etc) is a pi bond.

Tyler Angtuaco 1G

For strong acids (no kA value provided), observe bond length. For weak acids, the stronger acid is the one with a higher kA value (concentration of the products divided by the concentration of the reactants).

Tyler Angtuaco 1G

HCl has a longer bond between the two atoms, meaning that it is weaker and the H atom is easier to dissociate.

Tyler Angtuaco 1G

is AX3E also called bent AX3E would be trigonal pyramidal because there is a tetrahedral electron arrangement (bond angles of 109.5 degrees), but the lone pair reduces the bond angle because of repulsion. If you meant AX2E, yes, AX2E would be bent too. This is because there would be a trigonal plan...

Tyler Angtuaco 1G

Yes, it would be bent because electrons would position themselves on the same side of the atom rather than 180 degrees apart. This is due to the fact that lone pair - lone pair repulsion is strongest.

Tyler Angtuaco 1G

Tyler Angtuaco 1G

The image in the book does not include lone pairs, but to determine angle b, we have to consider the VSEPR shape of oxygen with the lone pairs in mind (lone pairs exist because of the octet rule). Keeping in mind that lone-pair to lone-pair repulsion is strongest, oxygen would have a tetrahedral ele...

Tyler Angtuaco 1G

The rules that help me the most are the octet rule, the expanded octet trend, and formal charge. Make sure each atom satisfies the octet rule before adding any left over electrons. If there are extra electrons, create multiple bonds or add lone pairs to atoms located in period 3 or below on the peri...

Tyler Angtuaco 1G

Ion-ion interactions are stronger than the dipole-dipole interactions of HCl, so it takes more energy (heat) to overcome ion-ion forces.

Tyler Angtuaco 1G

NO2- would have a bent molecular shape, preventing its dipoles from cancelling. N20 would be linear, causing its dipoles to cancel. Thus, NO2- has dipole-dipole interactions, which are stronger than the LDF that N20 only has.

Tyler Angtuaco 1G

There is a total of eight sides if you draw two pyramids, each with four sides.

Tyler Angtuaco 1G

Trigonal byprimadal electron arrangements have bond angles of 90, 120, and 180 degrees. Maybe you named the molecule by its electron arrangement rather than its molecular shape, which would differ since it only accounts for atoms and because its bond angles would be affected by lone pairs.

Tyler Angtuaco 1G

Atoms with larger radii are more easily polarizable. In other words, the electrons of larger atoms are easier to pull away from the nucleus of the atom. Thus, the polarizability of atoms increases down a group because size increases down a group (more electrons occupy more energy shells) and the out...

Tyler Angtuaco 1G

I3- would have a square pyramidal electron arrangement. If you picture the lone pairs of electrons being in the farthest positions away from each other (because repulsion of electron clouds between lone pairs are strongest), one would be on the axial atom (top of the pyramid), and two pairs would be...

Tyler Angtuaco 1G

How does a single electron compare to lone pairs in terms of repulsion? Assuming there was a molecule whose shape was square planar, with a lone pair on one axial position and a single electron on the other axial position, how would the bond angles differ from a molecule with the same shape but anot...

Tyler Angtuaco 1G

Which intermolecular forces arise between CO2 and H20, considering the fact CO2 is not a dipole? Can hydrogen bonds even form between the oxygen atoms of CO2 and the hydrogen atoms of H20?

Tyler Angtuaco 1G

Will electrons always occupy the equatorial position if given the option between that and the axial position?

Tyler Angtuaco 1G

Can someone explain the concept of overlapping orbitals and their effect on the strength of bonds?

Tyler Angtuaco 1G

Does anyone know the grading scale for final grades in this class?

Tyler Angtuaco 1G

When polar molecules are separated, how do their opposite partial charges on each molecule "merge and cancel" as stated in the textbook?

Tyler Angtuaco 1G

Can someone explain the trends between IMF forces in bonding and potential energy?

Tyler Angtuaco 1G

Can someone explain the difference between sigma and pi bonds in terms of their geometry and nodal planes?

Tyler Angtuaco 1G

Does anyone know which chapters from the book we will need to know for Test 2 based on Dr. Lavelle's outlines?

Tyler Angtuaco 1G

Electron affinity is a quantitative property of atoms which describes their likelihood of gaining an electron. Electronegativity, on the other hand, is a qualitative property that describes the pull an atom has on electrons.

Tyler Angtuaco 1G

It describes the wave qualities of an electron's orbital(s). It can be used to find electron probability density by squaring it.

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