CHEMISTRY COMMUNITY

Sartaj Bal 1J

For a forward reaction that is endothermic, increasing the equilibrium constant means that the forward rate constant will increase as well.

Sartaj Bal 1J

C is not considered because it has no effect on the rate. When the values of A and B are the same and C changes, the rate does not change, showing that C is indeed in zero order.

Sartaj Bal 1J

Since the equilibrium constant for a reaction is equal to the ratio of the rate constants for the forward and reverse reactions, and since the equilibrium constant is increasing for the forward reaction due to it being endothermic, that means the rate constant for the forward reaction is increasing ...

Sartaj Bal 1J

Minor detail, but in response to the above, I believe it's okay to approximate if the K value is 10^-4 or smaller.

Sartaj Bal 1J

This only applies to gases because liquids and solids are incompressible.

Sartaj Bal 1J

Since cell potential is an intensive property, one that does not change as the amount of matter changes, the cell potential does not change when the mass of electrodes changes.

Sartaj Bal 1J

The cathode concentration is considered the reactant because we were told to make the lower concentration out of the two the product. Usually, the anode has a lower concentration in a concentration cell, making it the product.

Sartaj Bal 1J

A positive potential difference between the electrodes signals that electrons are flowing from the left to the right or from the anode to the cathode, signifying which is which.

Sartaj Bal 1J

Halving the mass of the electrode should not affect the cell potential because voltage difference is the same and does not depend on how many times the reaction occurs/how much of the substance that makes up the electrode is present.

Sartaj Bal 1J

To add to the response above, when calculating Ecell for a concentration cell, always make the lower concentration the product for Q. For a general galvanic cell, the standard reduction potential is calculated using the table of reductional potentials. In a concentration cell, the standard reduction...

Sartaj Bal 1J

The way I think of it is as opposites. If something is being reduced (gaining an electron), that means it is taking an electron away from something, therefore making it an oxidizing agent.

Sartaj Bal 1J

In electrolysis, e- current is used to drive the non spontaneous redox reaction for converting electrical energy into chemical energy. In a galvanic cell, e- transfer changes chemical energy to electrical energy.

Sartaj Bal 1J

There is no difference between the two and they are considered to be a "battery" because of converting chemical energy to electrical energy.

Sartaj Bal 1J

ln Q is changed to log Q because biological systems are sensitive to pH. log is the appropriate way to calculate pH.

Sartaj Bal 1J

The key point is that the rate is made equal to the rate law equation with the concentrations inputted into their respective spots. Then, after division, the rate side is equal to 2 and the rate law side is equal to 2^m.

Sartaj Bal 1J

E stays the same because it is an intensive property. This a property of matter that does not change as the amount of matter changes.

Sartaj Bal 1J

The potential difference between electrodes is usually done by subtracting the left (anode, oxidation half reaction) from the right (cathode, reduction half reaction). If the result is positive, that means electrons are flowing from the left to the right, from the anode to the cathode, which is usua...

Sartaj Bal 1J

A salt bridge comes is significant to a galvanic cell because it eases the charge buildup . It allows the ions to transfer when which allows the solutions to stay neutral overtime. Why do the solutions need to stay neutral? The solutions need to stay neutral because if the charge builds up, the tra...

Sartaj Bal 1J

"n" in electrochemistry refers to the number of moles of electrons transferred. It is usually found using the same methods as before: using the given values to isolate n in the required equation.

Sartaj Bal 1J

Some half reactions have no conducting solids so it is necessary to use an inert conductor (platinum for example) as an electrode to transfer electrons. For the reaction, 2Fe3+ + Cu yields Cu2+ + 2Fe2+, platinum (s) is part of the cathode.

Sartaj Bal 1J

The standard reaction enthalpy for the formation of one mole of a substance from its element in their most stable form is called the standard enthalpy of formation. By definition, the standard enthalpy of formation of an element in its most stable form is zero.

Sartaj Bal 1J

An example of this first law of thermodynamics being implemented is the universe. The universe is an isolated system, therefore the energy of the universe is constant.

Sartaj Bal 1J

The Boltzmann equation is used to represent the relationship between degeneracy, w, and entropy. Degeneracy is the number of ways of achieving a given energy state. The Boltzmann equation also includes the Boltzmann constant which is 1.381*10^-23 J*K^-1.

Sartaj Bal 1J

Enthalpy is the study of heat released or absorbed in chemical reactions and physical changes. It is considered a state property as its value is determined by its current state. Heat is the transfer of energy due to temperature differences. It depends on the path taken and is therefore not a state p...

Sartaj Bal 1J

A reversible process is one that can be reversed by an infinitely small change in a variable (infinitesimal). Usually the work a system can do is greatest in a reversible process. This is approximated as the maximum amount of work that can be performed.

Sartaj Bal 1J

Why is the value of Cp,m 75.3 J K^-1 mol^-1 in this problem?

Sartaj Bal 1J

For phase change problems, I would suggest taking everything into account one step at a time. In this case, the ice first has to melt (1) and then go to the final temperature (2). So there would be two components. The water in the glass just has to go to the final temperature (1). Hope this helps!

Sartaj Bal 1J

I believe this is for molecules like benzene to take into account resonance. In the molecular structure, some of the carbon-carbon bonds will be single bonds and others will be double bonds.

Sartaj Bal 1J

Since Kr is a single atom, the above values are appropriate for this question. If the molecule is linear, Cv=5/2R and Cp=7/2R. If the molecule is non-linear, Cv=3R and Cp=4R. This is usually done under ideal gas conditions.

Sartaj Bal 1J

Like the above post mentions, a good way to think about is in stoichiometric terms. Just make sure each individual conversion makes sense and relates to the amount of moles in the chemical equation provided.

Sartaj Bal 1J

Steam is not hotter than boiling water at 100 C but will be carrying more energy because of the energy input required to change the phase. As a result, there is a large enthalpy for condensation and when the energy is released on skin, there is a more severe burn.

Sartaj Bal 1J

The standard reaction enthalpy is the reaction enthalpy when all the reactants and products are in their standard state at 1 atm. The standard enthalpy of formation refers to the standard reaction enthalpy for the formation of one mole of substance from its element in their most stable form. The sta...

Sartaj Bal 1J

A microstate is the state of the system defined in terms of the current behavior of all the constituent atoms. It can also be referred to as an arrangement or distribution. All the examples we discussed in class had the same energy.

Sartaj Bal 1J

How is a reaction determined to be spontaneous or not based off of its entropy?

Sartaj Bal 1J

The universe is also considered an isolated system; therefore the energy of the universe is constant.

Sartaj Bal 1J

All of the above answers are correct. Something that I found helpful to remember regarding the differences between a system and its surroundings is the ocean analogy. Spilling half a liter of water into the ocean doesn't affect its pressure.

Sartaj Bal 1J

Enthalpy is considered a state property because its value is determined by its current state. It is not dependent on the path taken to obtain that state. State properties can also be added and subtracted.

Sartaj Bal 1J

A phase change is a change from one state (solid, liquid, or gas) to another. Because heat is required during melting or boiling (phase transition), the temperature of the sample remains constant even though heat is being supplied.

Sartaj Bal 1J

In the example provided in class, the reactants of the chemical reaction are graphite (the most stable form of C), and H2 and O2 which all combine to form ethanol. All the reactants have an enthalpy of formation of 0 kJ/mol due to being in their most stable form.

Sartaj Bal 1J

In addition to the response above, most reactions are already provided in their standard state. When all reactants and products are in their standard state, the reaction enthalpy is called standard reaction enthalpy.

Sartaj Bal 1J

Endothermic reactions usually have a positive Delta H which signifies that heat is absorbed while exothermic reactions usually have a negative Delta H which signifies that heat was released during the competition of the reaction.

Sartaj Bal 1J

DesireBrown1J wrote:Do sig figs matter in this one? I did 3 sig figs for the equilibrium molar concentration because Kc had 3 sig figs, yet the solutions manual answer was in 2 sig figs.

I believe the answer is in 2 sig figs because the equilibrium constant, K, is 0.031 which has two sig figs.

Sartaj Bal 1J

Due to there being an equal number of moles of gas on both sides of this reaction, compressing the system (decreasing the volume) does not favor any direction. Had there been more moles of gas on the left, then the reaction would have shifted right and if there had been more moles of gas on the righ...

Sartaj Bal 1J

The above explanation is correct. A way to try this mathematically is to come up with different concentrations/partial pressures of O2 and O3 that allow for the same ratio. Then, substitute these values into two separate equations for the equilibrium constant that includes the respective exponents. ...

Sartaj Bal 1J

I believe the answer is 1.4 (2 sig figs) because the equilibrium constant, K, is .031 which also has two sig figs.

Sartaj Bal 1J

Ideally, you would want to wait until your final answer to include sig figs in order to save time and maintain accuracy throughout the problem.

Sartaj Bal 1J

For our purpose, we are mainly using the ideal gas equation to convert between concentration and partial pressure for a gas so I don't believe it's necessary to know the volume.

Sartaj Bal 1J

K is given by dividing the product partial pressures or molar concentrations by those of the reactants. If K is small, which is less than 10^-3, that means there are more reactants at equilibrium (denominator is bigger), and equilibrium "sits to the left". K=1 is rare and any value conside...

Sartaj Bal 1J

Q, the reaction quotient, is calculated at any time during the reaction when the concentrations are different than at equilibrium and is usually compared to K, the equilibrium constant, to determine which direction a reaction will proceed. In this case, K will already be known so if the calculated v...

Sartaj Bal 1J

Usually, the stoichiometric coefficients of the balanced equation are the exponent for each compound in the equilibrium equation. As long as all the products are placed in the numerator and all reactants in the denominator, the equation should work.

Sartaj Bal 1J

Is the chemical activity of a compound equal to the molar concentration? And is that why the concentration is used to find the equilibrium constant?

Sartaj Bal 1J

Usually, in problems like these, it is implied to use the given measurement in the equation. Since the uncertainty in velocity was greater than the speed of light, the model of electrons being in the nucleus is proven as invalid.

Sartaj Bal 1J

Usually, since H bonds are a stronger IMF, their melting and boiling points will be higher. For non polar molecules, these values increase as the molecules get larger because more LDF take place.

Sartaj Bal 1J

I believe it was 14 binding sites because each oxygen has 2 lone pairs which accounts for 6 sites, and then there are four hydrogens and four nitrogens with a lone pair. Thus accounts for H bonding because the H is attached to an electronegative atom (O, F, N) and the electronegative atoms mentioned...

Sartaj Bal 1J

My TA also mentioned knowing Plumbate for Lead (Pb).

Sartaj Bal 1J

In response to the previous post, I believe a lower pKa and larger Ka are actually representative of a strong acid. A higher Ka value is indicative of a larger concentration of hydronium (H3O+) ions.

Sartaj Bal 1J

I would try to memorize all the strong acids (HCl, HNO3, H2SO4, HBr, HI, HClO4, and HCl03). A common mnemonic to remember them is I, Cl, Br, No, Clo, Clo, So.

Sartaj Bal 1J

Can someone clarify what Professor said about coordination compounds and alphabetical order during lecture?

Sartaj Bal 1J

A biological example would be cisplatin, a well know chemotherapy drug. It has four ligands, 2 Cl's on the same side and 2 NH3's on the other side. They have a lone pair bonded to the central platinum metal atom. Hence, the terminology "Cis" is used.

Sartaj Bal 1J

Also, if the equilibrium constant, Ka, is given in a problem then this indicates that a weak acid is involved. In high school, my class remembered the strong acids through the mnemonic I, Cl, Br, No, ClO, ClO, So.

Sartaj Bal 1J

OH2 is used to emphasize that a lone pair from the oxygen is bound to the central metal atom. Usually, OH2 is on the right side of the molecule while H2O is located on the left side on the molecule since Oxygen is closest to the central metal atom with this specific configuration.

Sartaj Bal 1J

If we are given a molecule with multiple carbons, the structure will not always be in the form of a ring. For example, C4H10 forms a hydrocarbon chain with all the carbon atoms in the center covalently bonded to each other and the hydrogens at the terminal ends. There is no direct central atom becau...

Sartaj Bal 1J

There is only one Nitrogen atom which hints that the molecule is not symmetric. Nitrogen has a greater electronegativity than carbon so it has a greater electron density. These factors help predict that C5H5N is a polar molecule without drawing the Lewis structure.

Sartaj Bal 1J

If a molecule only has non polar bonds, then the it will be non polar. Usually when a molecule has a lone pair, it is polar. However, in molecules like XeF4 (2 lone pairs), the dipole moments and lone pairs cancel out, rendering the molecule non polar. Hope this helps!

Sartaj Bal 1J

http://everythingchemistryml.weebly.com/boiling-and-melting-points.html The graph on the above website illustrates the relationship between the three main states of matter (solid, liquid, gas) and the melting and boiling points. Usually, the straight line is longer at the boiling point to show that ...

Sartaj Bal 1J

Polarizing power is the ability of a cation to cause distortions in another atom's or ion's electron cloud. In general, the smaller and more highly charged the cation, the stronger the polarizing power. This is because the smaller radius allows the nucleus of the cation to maintain a stronger pull o...

Sartaj Bal 1J

It can be determined if a molecule has linear shape by looking at the number of bonding and lone pairs on the central atom. For example, molecules with the VSEPR notation of AX2 and AX2E3 both have linear shapes.

Sartaj Bal 1J

Gaining familiarity with all the aspects of the VSEPR theory chart (electron and molecular geometry, hybridization, and bond angles etc.) would be extremely useful for problem solving in this unit.

Sartaj Bal 1J

Your setup is correct. In this situation, all the bond angles would be slightly less than 109.5 degrees because the lone pair equally repels all the bonded electron pairs.

Sartaj Bal 1J

I don't believe the location of lone pairs around a central atom can be ascertained in a Lewis structure. The key point for VSEPR and hybridization is that each lone pair represents a region of electron density.

Sartaj Bal 1J

The A represents the central atom, X represents the bonds to central atom, and E represents the lone pairs on the central atom. The subscript on X and E denote how many bonds and lone pairs are present respectively. Hope this helps!

Sartaj Bal 1J

@405335722 the Bronsted-Lowry acid base model states that protons are either accepted or donated.

Sartaj Bal 1J

The sum of the formal charges of each atom in a Lewis structure must equal the charge of the overall ion. If the molecule is neutral, you want the sum of the formal charges to be 0. Usually more electronegative atoms are located at the outer edge of molecules. In resonance hybrids, electrons are del...

Sartaj Bal 1J

How does the addition of a lone pair impact bond angles in a molecule?

Sartaj Bal 1J

In a sigma bond, electron density is usually concentrated between the nuclei of the two bonding atoms. In a pi bond, the electron density is usually concentrated below and above the plane of nuclei in the two bonding atoms. A single bond is referred to as a sigma bond. In a double bond or triple bon...

Sartaj Bal 1J

An easy way to remember the pattern of polarizing power and polarizability is that cations need to be smaller and have a greater magnitude positive charge to have a higher polarizing power while anions need to be larger and have a smaller magnitude negative charge to have a higher polarizability. Th...

Sartaj Bal 1J

I believe we will not receive a period table that lists all the electronegativity of each element. However, it is best to know the relative trends to solve a variety of problems like creating a Lewis structure with the lowest energy arrangement of atoms and electrons.

Sartaj Bal 1J

And on a side note, when forming cations for the transition metals in the 3D sub shell, electrons are first removed from the 4S sub shell and then the 3D sub shell. For example, Mn4+ would have an electron configuration of [Ar] 3d3 instead of [Ar] 3d1 4s2. Both give the correct 3 valence electrons b...

Sartaj Bal 1J

Along with following the trends of lowest electronegativity/ionization energy for the central atom, a lot of molecules also tend to display some sort of symmetry. For example, CH4 achieves symmetry with the central atom, C, being surrounded by the four hydrogen atoms. Also, Hydrogen can never be the...

Sartaj Bal 1J

Usually, elements in the P-block of Period 3 or later periods have the ability to form an expanded octet. For example, we can compare Nitrogen in Period 2 and Phosphorus in Period 3. P is a larger atom than N as demonstrated by the greater atomic radius so as a result, it is an exception to the octe...

Sartaj Bal 1J

This is all great! Also, for formal charges, I would make sure that the negative charges are on the most electronegative atom of the molecule. This because these atoms have a higher affinity for electrons in comparison to others.

Sartaj Bal 1J

Our TA said that we can use the normal orientation as well. Px, py, and pz refer to the different possibilities of axis (x, y, or z) that p-orbital is on.

Sartaj Bal 1J

I combined the equations E equals Planck's constant times frequency and the speed of light equals wavelength times frequency to get wavelength equals Planck's constant times the speed of light all over energy. The energy is what you calculated in the first step converting keV to J. Hope this helps!

Sartaj Bal 1J

Transition metals can use their d electrons for bonding due to an incomplete d subshell. Therefore, a transition metal's valence electrons include the ns and (n-1)d electrons. In this case, Manganese would have 7 valence electrons.

Sartaj Bal 1J

Electron affinity is defined as the energy released when electrons are added to the gas phase atom. It increases from left to right across periods and upwards for groups. For groups, this occurs because as principal quantum number increases down a group, the size of the orbital increases (atomic rad...

Sartaj Bal 1J

To express the wave function in three dimensions, the three quantum numbers (n, m, and ml) need to be used. This is known as the atomic orbital, or the region of space where the electron is located.

Sartaj Bal 1J

A nodal plane is where there is zero probability of electron density or of finding an electron. The S-orbital has a spherical shape and hence a symmetric electron density distribution so it has no nodal planes.

Sartaj Bal 1J

With regards to the photoelectric effect and wave model of light, doubling the intensity (greater amplitude for wave) of the light source should have emitted electrons. Energy was correlated to intensity. However, this result did not occur. For the photon model, intensity correlates to increasing th...

Sartaj Bal 1J

The detector also has a slight positive charge which helps electrons in this situation drift towards it because opposite charges attract. As a result, the electron is counted as "ejected".

Sartaj Bal 1J

The key observation in worked out photoelectric effect problems is that when an ejected electron has 0 kinetic energy, the energy of the photon is equal to the energy required to remove the electron. The example in lecture based off this premise asked what could be the longest wavelength light to ac...

Sartaj Bal 1J

To add on, atomic radius increases down a group with each new period because the outermost electrons occupy shells with increasing principal quantum number and therefore lie farther from the nucleus. Atomic radius decreases across a period because new electrons are in the same shell of the atom and ...

Sartaj Bal 1J

Also, a catalyst may be identified in a chemical reaction with an element written above the "yield" arrow.

Sartaj Bal 1J

A helpful way to recall significant figures is to use the Atlantic and Pacific example. Atlantic, used in the ABSENCE of a decimal point, means to start from the right side of the number (the Atlantic Ocean is on the right side of the country) and go towards the left. Significant figures are counted...

Sartaj Bal 1J

Usually, in the textbook it is specified whether the molecule is solid, liquid, gas, or does/does not form a precipitate. If the solubility is not given, the solubility rules such as CASH N' Gia can be referred to.

Sartaj Bal 1J

An alternative way to approach this problem is to start by converting the 2.111 g of Na2CO3 to moles and then divide that value by 250.0 ml to calculate the concentration (molarity) of Na2CO3. Then for each component of the problem, start converting mmol and mg to mol and g, respectively. For parts ...

Sartaj Bal 1J

I don't believe it is necessary to convert from pm to km. Pm to m should be fine because a meter is the SI fundamental base unit. This can be done with 1 meter= 1*10^12 pm.

Sartaj Bal 1J

The mole ratio of anhydrous copper (II) sulfate to copper(II) sulfate pentahydrate is 1 to 1 because there is 1 mole of CuSO4 in 1 mole of CuSO4 * 5 H2O. Another example of this would be finding the moles of H in H2O. The ratio in this example would be 2 moles of H for 1 mole of H2O. I hope this hel...

Sartaj Bal 1J

If the V2 value provided is in milliliters, then the V1 could be directly solved for in milliliters because the units match up. If the V2 is in liters, you could either convert it to milliliters before solving for V1 or solve for the value of V1 in liters and then convert it to milliliters. Hope thi...

Sartaj Bal 1J

For the first stage of the process, I started with the Fe. Since the reactant side has 2 atoms of Fe while the products side has 3, the lowest common multiple of those two is 6. As a result, the reactant Fe2O3 receives a stoichiometric coefficient of 3 while the product Fe3O4 receives a stoichiometr...

Sartaj Bal 1J

Problem M19 is an example of combustion so the reactants are caffeine and oxygen while the products are carbon dioxide, water, and nitrogen. The grams of each product are used to convert to the grams of a specific atom of that product. For example, the amount of CO2 is used to find the amount of C, ...

Search found 101 matches