CHEMISTRY COMMUNITY

armintaheri

The rate law is an equation that gives you the reaction rate.

For example:
$r=k[A][B]$

$r$ is the rate, and $r=k[A][B]$ is the rate law.

armintaheri

a) You use a comma when there are two species in the same phase. For example, if $Fe^{2+}$ is being oxidized to $Fe^{3+}$ in the anode, you use a comma to separate them in the cell diagram, instead of a vertical line.

b} Yes, you use a conductor (usually platinum) when no solid is present.

armintaheri

You have to use the Van't Hoff equation: ln(\frac{k_{2}}{k_{1}})=-\frac{\Delta H}{R}(\frac{1}{T_{2}}-\frac{1}{T_{1}}) Plug in values: ln(\frac{k_{2}}{10^{-14}})=-\frac{58000}{8.314}(\frac{1}{303.15}-\frac{1}{298.15}) Solve for k_{2} : k_{2}=1.3\times 10^{-14} pk_{2}=-...

armintaheri

I think the order of the reaction has to be determined experimentally. You can't just look at a reaction and tell what order it is. 2A -> B + C looks like a second-order reaction but it doesn't have to be one. What if the reaction took place in two steps and involved the intermediate molecules X and...

armintaheri

It's actually the opposite. The fast step does not affect the overall rate because the overall reaction is only as fast as its slowest step. No matter how fast other reactions run, the overall reaction can't be completed until the slowest step is completed. Therefore, the rate of the overall reactio...

armintaheri

125-175=50
0.4(125)=50
The two ways of writing it are equivalent. You must be making a mistake elsewhere.

armintaheri

There is no way to figure out which step is fast or slow since this is determined experimentally. The question will always tell you which step is the slowest.

armintaheri

The activation energy doesn't matter. A reaction is spontaneous when the products have lower energy than the reactants, making $\Delta G$ negative.

armintaheri

It depends on the sum of all exponents in the rate law. The rate law can only be calculated experimentally.

armintaheri

P_J is the partial pressure of a gas and n_J is the number of moles of that gas. Other than that it's just the ideal gas law PV=nRT.

armintaheri

I believe temperature is the only thing that affects k. An increase in temperature increases k by increasing the odds of collision between reactant molecules.

armintaheri

For example, if one mole of Fe were being oxidized to Fe2+, n would be 2 because 2 moles of electrons would be transferred. If Fe had a coefficient other than one, you would multiply it by 2.

armintaheri

The reaction is spontaneous when delta G is negative, nonspontaneous when delta G is positive, and at equilibrium when delta G is 0

armintaheri

You would only put that in your diagram if the question says a platinum electrode is used. You would generally use a platinum electrode when the actual substances you're working with are gases.

armintaheri

When balancing oxygen in basic solution

armintaheri

By the highest power in the reaction quotient

armintaheri

I know oxygen is being reduced on one side and oxidized on the other (its oxidation number is 0 in $O_{2}$ and -2 in $OH^{-}$ so electrons are going from the left side to the right side). But I'm not really sure why electrons are going one way and not the other. Can someone explain this?

armintaheri

I think you can look at the individual free energies. The one with a smaller G will be the more stable one. But a negative \Delta G for the reaction tells you the same thing so you could just look at that instead of looking at two numbers. I can't think of any reason why you wouldn't get the same re...

armintaheri

All the questions I have seen in the textbook tell you what kind of solution it is

armintaheri

1. Because the ions in solution are not exchanging electrons. The solid electrodes are exchanging electrons. And the only way for them to do that is to send electrons through the wire. The ions that are dissolved in solution have already been oxidized/reduced, and do not participate in any more reac...

armintaheri

Can you be more specific about which equations you're talking about?

armintaheri

It's also important to remember that \Delta S is not entropy of a system, but the change in entropy as a result of that reaction. So if a reaction happens in multiple steps, and each of those steps causes a change in entropy, adding all those changes together gives you the total change as a result o...

armintaheri

I found a relatively accessible derivation of the formula here: http://www.eoht.info/page/S+%3D+k+ln+W

armintaheri

A reaction is spontaneous when \Delta G<0 \Delta G=\Delta H-T\Delta S \Delta H> 0 for boiling a liquid, because you are putting heat into the reaction. \Delta S> 0 for boiling a liquid, because gases are more disordered than liquids. So to make \Delta G<0 , all you have to do is raise the temperatur...

armintaheri

the change in energy of the system or delta U is equal to q+W. W is energy transferred to the system by work, while q is the energy transferred by heat.

armintaheri

I think the general rule is that you can ignore the second deprotonation if Ka2 is smaller than Ka1/1000.

armintaheri

You would need to use the heat of fusion. heat gained by ice = heat lost by water (heat needed to melt ice)(heat needed to warm melted ice)=(heat lost by water) (heat of fusion for water)(mass of ice)+(mass of melted ice)(heat capacity of water)(x-0)=(mass of water in the glass)(heat capacity of wat...

armintaheri

A closed system allows energy to leave and enter, but not matter. An isolated system allows neither energy nor matter to leave and enter. In reality, a thermos is a closed system because it does allow for the exchange of small amounts of energy (A hot drink eventually cools down in a thermos). But t...

armintaheri

Condensation is the transition from gas to liquid. Gas molecules have lots of energy because they are moving around quickly. To turn them into liquid, you have to slow them down significantly, by removing heat from them. Therefore, condensation releases heat.

armintaheri

Work is positive (done on the system) if it adds energy to the system. For example, if you increase the pressure of a gas using a piston, you are doing work on the gas because you are adding energy to it. If you heat a gas, you are adding energy to it, therefore you are doing work on it.

armintaheri

When all your reagents are gases, you can choose whether to use partial pressures or concentrations. But in this case, you have a gas on one side and an aqueous reagent on the other. You obviously can't convert the aqueous concentration to a partial pressure since it's not a gas. And you can't conve...

armintaheri

It's not really the change in pressure that affects the equilibrium, it's the change in concentrations. When you decrease the volume, there is less space for molecules to move around in. It gets more crowded. Let's say you have a reaction that has more moles on the reactants side. If you have a lot ...

armintaheri

I'm not sure if it's the right answer, but my guess is that hydronium and hydroxide ions don't really move through water, they only ionize the water molecules next to them, so the charge moves through the water, not the actual ion. Especially since the question says they "appear to move" f...

armintaheri

Exactly. If a reaction has solid reactants and aqueous products, a larger equilibrium constant means the reactants are more soluble.

armintaheri

If the reaction is exothermic, heat is released as a result of the reaction. Therefore, lowering heat is like removing a product and the equilibrium shifts toward the products.If the reaction is endothermic, removing heat is like removing a reactant, so the equilibrium shifts toward the reactants.

armintaheri

Ka is the dissociation constant for the acid. The higher the Ka the more completely the acid dissociates. Therefore high Ka corresponds to stronger acid. pKa is the negative log of Ka. So the smaller the pKa the stronger the acid.

armintaheri

Because solids and liquids don't have concentrations. They're pure substances. So including them makes no sense.

armintaheri

Q is the reaction quotient, which is the concentrations of products over the concentrations of reactants, with the coefficients as exponents. K is just the specific value of Q when the reaction is at equilibrium.

armintaheri

Since the reaction is not currently at equilibrium you would need to use an ICE table. For the initial concentrations, you would use the mol values provided divided by the volume (5L). Then you use the quadratic formula to find the changes in concentration, which would then give you the final concen...

armintaheri

$\frac{1}{}\lambda = R (\frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}})$

$\lambda = 1.0\textup{x}10^{-9} m$

$n_{1} = 1$

$R = 10 973 731.6 m^{-1}$

Plug in and solve for $n_{2}$ .

armintaheri

You would use the coefficients to find out exactly how much of one reactant you need to completely react with a given amount of the other reactant.

armintaheri

Uncertainty in momentum times uncertainty in position is greater than or equal to planck's constant over 4 pi. You are given the uncertainty in position. Plug it into the equation and solve the inequality.

armintaheri

Depends on the pollutant in question. Sulfur dioxide is a common example:

$SO_{2}+H_{2}O\rightarrow H_{2}SO_{3}$

armintaheri

a) Compound goes into water. It breaks up into Br - and NH 4 + . Br - doesn't do anything. Some of the NH 4 + release a hydrogen and become NH 3 . Releasing a hydrogen makes the solution acidic. pH falls below 7. b) Breaks up in water. The sodium does nothing. The carbonate is the conjugate base of ...

armintaheri

You're generally supposed to know the charges on common polyatomic ions. So you should know that CN has a -1 charge. If you don't know the charges beforehand, the name of the compound may also help you figure it out. The (II) in hexacyanoferrate(II) tells you that the iron has a +2 charge. Since the...

armintaheri

Original concentration: 10 x Concentration diluted to 12% of original value: (10 x )(0.12) Original pH: -log(10 x ) pH after dilution: -log((10 x )(0.12)) = -log(10 x ) - log(0.12) Change in pH = (Original pH) - (pH after dilution) = -log(10 x ) - (-log(10 x ) - log(0.12)) Change in pH = -log(10 x )...

armintaheri

Polarity has to do with asymmetry and difference in electronegativity. If there are polar bonds and the molecule is asymmetrical, then it's polar. Hybridization requires a little bit of thinking. You can think of the central atom having multiple electron "sites". A site can contain a bond ...

armintaheri

A permanent dipole happens when the molecule contains polar bonds and is asymmetrical. For example, doesn't have a permanent dipole moment because it contains no polar bonds. Carbon tetrachloride doesn't have a permanent dipole moment because it's symmetrical. Chloroform does have a permanent dipole...

armintaheri

I think you have that backwards. The concept of conjugates exists in Bronsted-Lowry, since it deals with proton exchange. An acid loses a proton and becomes its conjugate base, a base gains a proton becomes its conjugate acid. Lewis acids and bases don't always exchange protons. For example, BF 3 is...

armintaheri

Larger molecules/atoms have larger electron clouds which can be distorted to a greater extent, leading to stronger interactions.

armintaheri

The question is basically asking which compounds experience dipole-dipole interactions. You can eliminate A and E. A is nonpolar because carbon and hydrogen have almost identical electronegativities. E is nonpolar since the chlorines are symmetrically arranged around the carbon. So A and E will not ...

armintaheri

Electron promotion happens when an electron that used to be in an s orbital is pushed up to a higher energy level to allow for hybridization. For example, carbon has two electrons in 2s and two electrons in 2p. To hybridize, one electron is pushed from 2s up to 2p. Now there is one electron in 2s an...

armintaheri

Bond polarity exists on a spectrum. On one side you have covalent, on the other side is ionic. You could replace covalent with nonpolar and ionic with polar. The more polar a bond gets (more electronegativity difference between the atoms) the closer it gets to the ionic side, so you say it has more ...

armintaheri

Because energy is released when a bond forms. Since energy is leaving the system, the sign is negative.

armintaheri

I think what you're thinking about is atomic radius, which increases as you move down and to the left on the periodic table. As atomic radius increases, the distance between the nuclei of atoms in a bond increases, so the bond gets longer.

armintaheri

First step of drawing a Lewis structure: count your valence electrons. 7 from the chlorine and 6 from each oxygen gives you 19. Since there is a charge of +1, you have 18 valence electrons. Normally, chlorine would only be able to form one bond, since it only has one unpaired electron. But since we ...

armintaheri

Short answer: transition metals are the spawn of satan and they are out to ruin your life. Long answer: During ionization, 4s electrons are lost before 3d electrons. So if you removed three electrons and ended up with 3d 6 , that means you removed 2 electrons from 4s and 1 electron from 3d. So the o...

armintaheri

A radical is any molecule/atom that has unpaired valence electrons. Normally you want electrons to be either in bonds or in lone pairs. When an electron is not in a bond or a pair and it's just hanging out by itself, it's really reactive, and you call the molecule/atom a radical. You can draw Lewis ...

armintaheri

You fill the 4s first, just like the Aufbau principle tells you to. The only exceptions are Chromium and Copper. The reason those two are different is that orbitals want to be either full or half-full whenever possible. Aufbau tells you chromium should be [Ar]3d 4 4s 2 , but the actual configuration...

armintaheri

They are similar concepts with different applications. Electronegativity is only relevant in bonded atoms. The atom that attracts the electrons more in a bond has higher electronegativity. If the atoms are by themselves the concept of electronegativity is irrelevant. Electron affinity is a property ...

armintaheri

The 4s subshell is lower in energy than the 3d subshell, so it fills up first. The 4s becomes higher in energy after filling up, so if you ionize the atom, electrons are lost from the 4s subshell before the 3d subshell. But that's not how I learned it so it just confuses me to think of it that way. ...

armintaheri

It actually does, which is why a negative ion is always larger than a neutral atom of the same element. The trend you are talking about is atomic radii getting smaller as you move right in the periodic table. That happens because you're adding protons to the nucleus, which increases the pull on the ...

armintaheri

If two waves are in phase (peaks line up with peaks perfectly), the waves will interfere constructively and result in a wave of greater amplitude. If the waves are out of phase by half a wavelength (assuming they have the same wavelength) then they interfere destructively (peaks line up with troughs...

armintaheri

There are essentially two factors that determine ionization energy. There is the attraction between electrons and the nucleus, and the repulsion between electrons and other electrons. As you go from left to right on the periodic table, the number of protons in the nucleus increases, so the attractio...

armintaheri

The equation contains the Planck constant, which is usually given in $m^{2}kg/s$ . So you need to plug in masses in kilograms, otherwise the units won't cancel out properly.

armintaheri

First thing to notice is that it asks for the "net ionic equation." That means you only include reactants and products that are involved in a permanent or irreversible reaction. If you remember solubility rules, you know that any ionic compound containing nitrate or sodium is soluble in wa...

armintaheri

The question tells you that epsom salt consists of magnesium sulfate heptahydrate. The prefix hepta- means 7. If you weren't given the name of the compound or the chemical formula then you would have no way of knowing the coefficient for water.

armintaheri

It's not wrong. It's just unnecessary and unconventional. If you were going to publish a scholarly paper or something that contained chemical reactions, then you would obviously make sure not to include coefficients of 1 since it's against convention. But I can't imagine anyone taking points off for...

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