CHEMISTRY COMMUNITY

jessicasilverstein1F

Yes, catalysts always go from reactant to product and not the other way around

jessicasilverstein1F

Calculate the activation energy, Ea , in kilojoules per mole for a reaction at 70.0 ∘C that has a rate constant of 0.201 s−1 and a frequency factor of 6.04×1011 s−1 .

I am not sure where to begin with this one if anyone can help

jessicasilverstein1F

1st order: reaction will have a straight-line graph of ln[A] v. t
2nd order: reaction will have a straight-line graph of 1/[A] v. t
Zero order: reaction will have a straight-line graph of [A] v. t

Note that 1st and Zero have negative slope whereas 2nd is positive

jessicasilverstein1F

This is a first order reaction, so use the integrated law for first-order reactions: [A]= [A]0 e^-kt to solve for t. Also make sure that your units are correct because the answer is in minutes, not seconds.

jessicasilverstein1F

A certain reaction has an activation energy of 41.43 kJ/mol. At what Kelvin temperature will the reaction proceed 4.50 times faster than it did at 343 K?

I am not sure what the k1 and k2 values would be here. I am trying to use the Arrhenius equation if anyone can help

jessicasilverstein1F

Anode goes on the left and cathode goes on the right

jessicasilverstein1F

The only time you use platinum is when there is not a conducting solid in the redox reaction, in this case you add Pt(s)

jessicasilverstein1F

Arrange the following metals in order of increasing strength as reducing agents for species in aqueous solution: (a) Cu, Zn, Cr, Fe; (b) Li, Na, K, Mg; (c) U, V, Ti, Al; (d) Ni, Sn, Au, Ag.

Does anyone know what the rule for this is?

jessicasilverstein1F

A student was given a standard Cu(s)|Cu2+(aq) half-cell and another half-cell containing an unknown metal M in 1.00 M M(NO3)2(aq) and formed the cell M(s)|M+(aq)||Cu2+(aq)|Cu(s). The cell potential was found to be −0.689 V. What is the value of E°(M2+/M)? I am not sure where to begin with this one i...

jessicasilverstein1F

Write the half-reactions, the balanced equation for the cell reaction, and the cell diagram for each of the following skeletal equations: b) Ce4+(aq) + I−(aq) →I2(s) + Ce3+(aq) I am struggling to write the cell diagram for this one and I am not sure when using Pt(s) is appropriate if anyone can help.

jessicasilverstein1F

Write the half-reactions and the balanced equation for the cell reaction for each of the following galvanic cells:
(d) Pt(s)|O2(g)|H+(aq)∥OH−(aq)|O2(g)|Pt(s)

Can anyone help me with this problem?

jessicasilverstein1F

Balance each of the following skeletal equations by using oxidation and reduction half-reactions. All the reactions take place in acidic solution. Identify the oxidizing agent and reducing agent in each reaction. Reaction of chlorine in water: Cl2(g)→HClO(aq)+Cl2(g) I am having trouble balancing thi...

jessicasilverstein1F

Which of the reagents would oxidize Cr to Cr3+ , but not Fe to Fe3+?

Does anyone know how to determine this? I am a bit lost

jessicasilverstein1F

For a particular redox reaction, Cr is oxidized to CrO2−4 and Fe3+ is reduced to Fe2+ . Complete and balance the equation for this reaction in basic solution. The phases are optional.

Can anyone help me with this, I am not sure what I am doing wrong.

jessicasilverstein1F

The salt bridge is there to make sure there is electrical neutrality in each half cell and if you do not have this then one side would be positive and the other negative.

jessicasilverstein1F

Voltage is the same as the maximum cell potential, not maximum work.

jessicasilverstein1F

I always remember it that A comes before C in the alphabet and if you put the A on the left side this represents the anode going to the C on the right side cathode and the flow of the electrons is left to right

jessicasilverstein1F

LEO is an acronym that helps with understanding oxidation. It stands for "Loss of Electrons Oxidation" so oxidation is when there is a loss of electrons

jessicasilverstein1F

Yes, if looking in terms of per mol

jessicasilverstein1F

It is spontaneous under conditions that result in a negative delta G

jessicasilverstein1F

The notation of dq means a very small change in q over very small change in time. This is notation for integrals.

jessicasilverstein1F

G is not under standard conditions, whereas Gº is

jessicasilverstein1F

I agree i think it depends on what values you are given

jessicasilverstein1F

Calculate the equilibrium constant, K , at 25.0°C for each of the reactions. Use the thermodynamic information provided in the table. The first step in the synthesis of trichloromethane (chloroform) from natural gas (methane). CH4(g)+Cl2(g)↽−−⇀CH3Cl(g)+HCl(g) I am not sure how to do this, I have bee...

jessicasilverstein1F

There is a difference, ΔG° refers to Gibbs free energy under standard conditions and ΔG is not under standard conditions

jessicasilverstein1F

Calculate the standard molar entropy of vaporization of water at 60.0 °C , given that its standard molar entropy of vaporization at 100.0 °C is 109.0 J⋅K−1⋅mol−1 and the molar heat capacities at constant pressure for liquid water and water vapor are 75.3 J⋅K−1⋅mol−1 and 33.6 J⋅K−1⋅mol−1 , respective...

jessicasilverstein1F

Yes, you can assume this because the temperature stays constant in isothermal reactions

jessicasilverstein1F

The molar heat capacity for carbon monoxide at constant volume is CV, m=20.17 J/(K·mol) . A 12.00 -L fixed-volume flask contains CO(g) at a pressure of 8.00 kPa and a temperature of 25.0 °C. Assuming that carbon monoxide acts as an ideal gas and that its heat capacity is constant over the given temp...

jessicasilverstein1F

Automobile airbags contain solid sodium azide, NaN3, that reacts to produce nitrogen gas when heated, thus inflating the bag.

2NaN3(s)⟶2Na(s)+3N2(g)

Calculate the value of work, w, for the system if 26.9 g NaN3 reacts completely at 1.00 atm and 22 ∘ C

Can anyone help me with this?

jessicasilverstein1F

An 80.0 g sample of a gas was heated from 25 ∘C to 225 ∘C. During this process, 346 J of work was done by the system and its internal energy increased by 8025 J. What is the specific heat of the gas?

I am not sure how to set up this problem, any help is greatly appreciated!

jessicasilverstein1F

Heat capacity can never be negative because it is the heat required to raise the temperature of a substance by 1°C.

jessicasilverstein1F

For this you need to set up an equation where heat lost by the system =- heat absorbed by the system and use the q=mCdeltaT equation for both sides.

jessicasilverstein1F

The textbook uses J/gºC so I would use this.

jessicasilverstein1F

An ice cube with a mass of 50.2 g at 0.0 ∘C is added to a glass containing 394 g of water at 45.0 ∘C . Determine the final temperature of the system at equilibrium. The specific heat capacity of water, Cs , is 4.184 J/g⋅∘C , and the standard enthalpy of fusion, ΔH∘fus , of water is 6.01×103 J/mol . ...

jessicasilverstein1F

in this case, I do think that we need to consider phase changes as well

jessicasilverstein1F

A phase change is just any time that a substance changes from one phase to another

jessicasilverstein1F

I would assume this when x is lower than 10^-4

jessicasilverstein1F

Yes, this is true. Endothermic reactions will always have a + delta H, and exothermic reactions will always have a - delta H, this is the case for all

jessicasilverstein1F

For these questions it is important to draw out all lewis structures in the correct way. Then you can use this to subtract the reactions bonds minus products

jessicasilverstein1F

This summarizes Le Chatelier’s Principle that basically means when you disturb a system, the system will reestablish equilibrium by either shifting towards the products or towards the reactants to minimize the change.

jessicasilverstein1F

You need to know the sign of deltaH (whether the reaction is exothermic or endothermic) to determine this. This should be given to you in a problem.

jessicasilverstein1F

Unfortunately the only way to know whether something is a strong/weak acid/base is to memorize them!

jessicasilverstein1F

A careless laboratory technician wants to prepare 200.0 mL of a 0.025 M HCl(aq) solution but uses a volumetric flask of volume 250.0 mL by mistake. (a) What would the pH of the desired solution have been? (b) What will be the actual pH of the solution as prepared? Does anyone know where to start wit...

jessicasilverstein1F

Calculate the molar concentration of OH− in solutions with the following molar concentrations of H3O+: (c) 3.1 mol⋅L−1?

For part C, I keep on trying to calculate the pH of the solution by putting -log(3.1) in my calculator, but I keep getting a negative result. Is anyone else having this problem?

jessicasilverstein1F

A sample of ammonium carbamate of mass 25.0 g was placed in an evacuated flask of volume 0.250 L and kept at 25 °C. At equilibrium, 17.4 mg of CO2 was present. What is the value of Kc for the decomposition of ammonium carbamate into ammonia and carbon dioxide? Has anyone properly got this answer? My...

jessicasilverstein1F

Consider the reaction 2NO(g)⇌N2(g)+O2(g). If the initial partial pressure of NO(g) is 1.0 bar, and p is the equilibrium partial pressure of N2(g) in bar, what is the correct equilibrium relation?

Does anyone know how to answer this question? The text book says the answer is K=p2/(1.0−2p)2

jessicasilverstein1F

In an experiment, 0.020 mol NO2 was introduced into a flask of volume 1.00 L and the reaction 2NO2(g)⇌N2O4(g) was allowed to come to equilibrium at 298 K. (a) Using information in Table 5G.2, calculate the equilibrium concentrations of the two gases. (b) The volume of the flask is reduced to half it...

jessicasilverstein1F

This is just a given value that has been experimentally determined. 1.0 x 10^-14 for water at 25 degrees Celsius.

jessicasilverstein1F

Are bars the same unit as atmospheres? Refering to question 4 on sapling

jessicasilverstein1F

LeChatlier's principle states that reactions want to minimize the effect of changes in conditions of a system at equilibrium. So if anything changes like pressure temperature volume ect. the reaction will do the most to make sure this change does not affect the system at equilibrium

jessicasilverstein1F

I think you can use either way to describe a shift!

jessicasilverstein1F

Consider the reaction of NH3 and I2 to give N2 and HI. 2NH3(g)+3I2(g)↽−−⇀N2(g)+6HI(g)K Using two or more of the given equations, determine the equilibrium constant, K , for the reaction of NH3 with I2. H2(g)+I2(g)↽−−⇀2HI(g)I2(g)↽−−⇀2I(g)N2(g)+3H2(g)↽−−⇀2NH3(g)H2(g)+Cl2(g)↽−−⇀2HCl(g)Ka=160Kb=2.1×10−3...

jessicasilverstein1F

In this class, R is 8.314 J·K^-1·mol^-1.

jessicasilverstein1F

Is Qp, Qc, and Q all the same reaction quotient? I am not sure if they all mean the same thing.

jessicasilverstein1F

The reason why this is rare is because when K=1 this means that the concentration of reactants to products is equal. This means that the reactants and products are equally stable, and this is not usually the case, thus making K=1 rare.

jessicasilverstein1F

P = Pressure
V = Volume
n = number of moles
R = gas constant (in Kelvin)
T = Temperature (in Kelvin)

make sure all in right units

jessicasilverstein1F

Both Kp and Kc are equilibrium constants, but they measure different things. Kp measures partial pressures and Kc measures concentrations.

jessicasilverstein1F

It will always be in Kelvin. Be sure to make sure this is the value you have.

jessicasilverstein1F

Are there multiple equations for the reaction of acid rain?

jessicasilverstein1F

you use ate when the overall compound is negative. hope this helps!

jessicasilverstein1F

yes, a coordination compound can have multiple kinds of ligands bound.

jessicasilverstein1F

yes! that looks correct to me as well.

jessicasilverstein1F

yes. you should take into account lone pairs in hybridization. they are considered regions of electron density

jessicasilverstein1F

I usually look and see if it has both a H and an overall negative charge.

jessicasilverstein1F

I think that delocalized means that there are renosonce structures

jessicasilverstein1F

H2O (l) + CO2 (g) ⇌ H2CO3 (aq)
H2O can also interact with other compounds such as So4 to result in acid rain as well.

jessicasilverstein1F

each Cn has a negative one charge for a total of negative two, K has one positive charge. Therefore for the overall compound to be nuetral it should be Cu(I)

jessicasilverstein1F

There are four regions of electron density around the N (one lone pair and 3 bonds). Therefore this means that it is sp3 hybridized.

jessicasilverstein1F

I think about it as looking to see if there are two things both present: An availible H+ to be donated, and and overall negative charge.

jessicasilverstein1F

What does the answer key say? I believe that o2 has a nuetral charge and each Br has -1 so it should be nickel with +2 charge

jessicasilverstein1F

Ka is the acid dissociation constant. pKa is the negative log of the Ka value. When Ka increases the strength of the acid also increases and the pka decreases.

jessicasilverstein1F

The CH3COOH has a carboxyl group COOH. This helps in determining that it a weak acid.

jessicasilverstein1F

How exactly do we find the conjugate acid and base for a species? Do all species have these?

jessicasilverstein1F

Yes, if the pH is less than 7, it is acidic, and above 7 it is basic
You can find the pH from the pOH using the formula: 14 = pH + pOH

jessicasilverstein1F

pH + pOH = 14
pH = -log([H+])
pOH = -log9[OH-])
[H+] = 10^-pH
[OH-] = 10^-pOH

I hope this helps!

jessicasilverstein1F

These can be confusing to me. I think of it like this:
A conjugate acid is the resulting formula when a base accepts a proton (H+), and a conjugate base is the species that results when an acid gives off a proton (H+).

jessicasilverstein1F

They are different definitions based on proton donating, accepting or electron donating, accepting.
Lewis acid accept electrons while lewis base donate electrons.
Bronsted acid gives proton, while bronsted base accepts protons.

jessicasilverstein1F

the main difference is that a lewis acid is an electron acceptor and a lewis base is an electron donor

jessicasilverstein1F

I believe that it could be either, in this case.

jessicasilverstein1F

The coordination number is the number of bonds present. Both square planar and tetrahedral have four bonds.

jessicasilverstein1F

The oxidation state is the charge of an atom.

jessicasilverstein1F

I think we are supposed to memorize these, however I am not sure if it will be given. I use this
https://sites.google.com/site/chempendix/ligands

jessicasilverstein1F

I had a similar problem. The cobalt has an oxidation state of +3 and not +2 because each Cl has a -1 charge and NH3 is a neutral compound. It is not +2, but is +3. Hopefully that helps

jessicasilverstein1F

I think you do it for the entire compound, not just what is in the brackets

jessicasilverstein1F

Classify each of the coordination compounds according to the coordination number.

How do you determine coordination number, and is this separate from oxidation number?

jessicasilverstein1F

[Co(NH3)4Cl2]Cl :

Does anyone know how to arrange the ligands in alphabetical order here? Is it based on tetra and di or is it based on ammine and chloro?

jessicasilverstein1F

sigma bonds are single bonds and pie bonds are double bonds

jessicasilverstein1F

How do we know what compounds form delocalized pie bonds, what does delocalized mean?

jessicasilverstein1F

H2O and OH2 is the same compound they are just written in a different order to show that the lone pairs on the O are what is bonding and forming the coordinate covalent bond with the transition metal cation.

jessicasilverstein1F

Yes, you should count the double bond as two bonds in this case.

jessicasilverstein1F

Yes. Both lone pairs and bonding pairs are regions of electron density.

jessicasilverstein1F

Draw the three possible structures of C3H4 . Be sure to include all atoms.

I am not sure how to draw the last structure for this?

jessicasilverstein1F

The reason that H20 is bent is because the oxygen has two lone pairs. These lone pairs cause repulsion of the two hydrogen atoms and pushes them downwards, thus causing a bent structure in the molecule

jessicasilverstein1F

Yes, I think it will differ based on the exact atoms involved. This is because of the difference in the electronegativity of the atoms involved in bonding

jessicasilverstein1F

For each molecule, specify the polarity of the bonds and the overall polarity of the molecule.
How would we know if specific bonds are polar versus nonpolar versus the overall molecule being polar or nonpolar itself?

jessicasilverstein1F

How many outer atoms and lone pairs are present in a molecule with a square pyramidal shape?

How are we supposed to determine this?

jessicasilverstein1F

The reason for this is that there is a lone pair on the S atom in SO2. This then distorts the molecule and repels the atoms down into a bent molecular shape

jessicasilverstein1F

You would want to place the double bond wherever it makes the formal charges closest to zero

jessicasilverstein1F

Give the ground-state electron configuration and number of unpaired electrons expected for each of the following ions: (a)
Ca2+;(b) In+; (c) Te2−; (d) Ag+

I am not sure how to determine how many unpaired electrons there are

jessicasilverstein1F

One thing that helps me is using the acronym FONClBrISCH from F being most electronegative in the periodic table

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