CHEMISTRY COMMUNITY

Angela G 2K

Just tried switching k1, k2, T1, T2 and the answer was the same, so I guess the order doesn't matter. Just make sure the you use the correct temperature for their respective rate constants. Mathematically it works out, since a higher temperature gives a larger rate constant. If you use the bigger te...

Angela G 2K

You don't need lnA here. You have the rate constant at 800 deg C and the question asks for the rate constant for the same reaction at 700 deg C, so you have these two equations: At Temp 1 = 800 C = 1073 K: lnk_{1}=lnA-\frac{E_{a}}{RT_{1}} At Temp 2 = 700 C = 973 K: lnk_{2}=lnA-\frac{E_{a}}{RT_{2}} C...

Angela G 2K

I think they're just asking for the rate laws of each individual step, not the overall reaction. For the overall reaction you wouldn't keep the intermediate in the rate law for the slow step and would instead substitute it using the pre-equilibrium approach.

Angela G 2K

You can derive the units of k by plugging in [A] = mol.L-1 and t = s into the integrated rate laws and solving for k. (this is basically 15.9 in the textbook) Zero order: [A]_{0}-[A] = kt \rightarrow k=\frac{[A]_{0}-[A]}{t}=\frac{[mol\cdot L^{-1}]-[mol\cdot L^{-1}]}{s} k = mol\cdot L^{-1}\cdot s^{-1...

Angela G 2K

The question gives the rate constant 25 C as 1.5x10^10 L.mol-1.s-1, indicating a second order reaction. The question asks for the rate constant of the same reaction but at 37 C, given an activation energy of 38 kJmol-.1. The answer I got was 2.7x10^10 L.mol-1.s-1, but the answer in the back of the b...

Angela G 2K

a) What is the overall reaction for the following mechanism? ClO- + H2O -> HClO + OH- (fast equilibrium) HClO + I- -> HIO + Cl (very slow) HIO + OH- -> IO- + H2O (fast equilibrium) The answer in the back of book says the overall reaction is ClO- + I- -> IO-. Where did the Cl go? Why isn't it ClO- + ...

Angela G 2K

For a reaction aA + bB -> cC + dD, where the lowercase letters are the stoichiometric coefficients and the uppercase letters are chemical species, the unique rate law is -\frac{1}{a}\frac{d[A]}{dt} = -\frac{1}{b}\frac{d[B]}{dt} = \frac{1}{c}\frac{d[C]}{dt} = \frac{1}{d}\frac{d[D]}{dt} This rate law ...

Angela G 2K

Half-life is just the time needed for the concentration to reach half its initial concentration. That definition is the same no matter the order of the reaction. To get the half-life equation from each different rate law, just set t=t1/2, and [A]=1/2 {A}0, and then just algebraically separate t1/2 f...

Angela G 2K

Thermodynamics predicts the spontaneity, while kinetics predicts the rate/speed of the reaction. If a reaction is spontaneous (thermodynamically unstable) but the reaction doesn't occur at a measurable rate, then it is controlled by kinetics (kinetically stable). For example, C(diamond) spontaneousl...

Angela G 2K

Not sure about part b, but it looks like they just took each reactant, put H2O(l) on the product side, and balanced the equation. For part c, KOH is there because you can't put in OH- by itself, so you add in K to make it a solution. NaOH would probably work as well. Although KOH is on the reactant ...

Angela G 2K

I think it's because the oxidation number for bromine doesn't change - for the reactant AgBr, Ag has oxidation no. = +1, and Br has oxidation no. = -1 for an overall charge of 0. So in the anode, Ag(s) + Br- -> AgBr + e (Ag goes from 0 to +1); cathode, Ag+ + e -> Ag(s) (Ag goes from +1 to 0). The ce...

Angela G 2K

Here is the question: The body functions as a kind of fuel cell that uses oxygen from the air to oxidize glucose: C6H12O6(aq) + 6O2(g) -> CO2(g) + 6H2O(l) During normal activity, a person uses the equivalent of about 10 MJ of energy a day. Assume that this value represents delta G, and estimate the ...

Angela G 2K

Did you mean something else? You can't have a reversible free expansion because free expansion is irreversible, since the gas expands in a vacuum. In a reversible reaction P(external) = P(internal), which doesn't work in free expansion where there is no external pressure.

Angela G 2K

Delta nRT is used to calculate the change in internal energy under constant pressure. Delta U = q + w, but under constant pressure it becomes \Delta U=\Delta H-P\Delta V A change in volume is often due to a net change in gas molecules, so P\Delta V=\Delta nRT . Substitute in and you get \Delta U=\De...

Angela G 2K

Using the equation of broken-formed, we should get (\frac{1}{2}(N\equiv N) + \frac{5}{2}(H-H)+ (O=O)+ 2(Hsub(C))) - (2(N-H) + (N-C)+2(C-H)+(C-C)+(C=O)+(C-O)+(O-H)) Giving you (1/2(944) + 5...

Angela G 2K

In a galvanic cell, the anode is usually on the right and is the site of oxidation, and generally gets thinner over time as the metal electrode loses electrons and gives off metal ions. The cathode is on the left and is the site of reduction, and gets thicker over time as the metal ions gain electro...

Angela G 2K

Cv,m is the molar heat capacity in constant volume, and Cp,m is the molar heat capacity in constant pressure. For liquids and solids, Cv,m and Cp,m are similar. For ideal gases, Cv,m = 3/2 R and Cp,m = 5/2 R.

Angela G 2K

Yes, $\Delta G^{o}=-nFE^{o}(cell)$
Where n is the number of moles and F = Faraday's constant = 9.6485 x 10^4 C*mol^-1

Angela G 2K

Enthalpy tends to go from high enthalpy to low enthalpy, whereas entropy tends to go from low entropy to high entropy. Delta H -, Delta S + = favored Delta H -, Delta S - = favored at low temperatures only Delta H +, Delta S + = favored at high temperatures only Delta H +, Delta S - = not favored (r...

Angela G 2K

An exothermic process leads to an increase in the entropy of the surroundings, since delta S (surroundings) = - (delta H)/T. For an exothermic reaction, the change in enthalpy is negative, making the change in entropy of the surroundings positive. The entropy of the system will not increase, but the...

Angela G 2K

A greater dipole moment means that the molecules experience more attraction to one another and lie head-to-tail in a more orderly fashion, so their residual entropy is lower. Molecules with smaller dipole moments can be in either direction, resulting in a higher residual entropy.

Angela G 2K

Not sure if this helps, but in a reversible reaction P(in) and P(ex) is the same, whereas in an irreversible reaction P(ex) differs by P(in) by a measurable amount.

Angela G 2K

Snow is formed when temperatures drop low enough for water to change from a liquid to a solid, which is an exothermic process - as the surroundings cool, heat is transferred from liquid water into the surroundings, and the water solidifies into snow.

Angela G 2K

For the first reservoir, heat is being transferred out and into the second reservoir, so the change of entropy is negative.

Angela G 2K

Br2 was initially a liquid. Since all bond enthalpies refer to species in the gas phase only, Br2 needs to be vaporized (liquid to gas) and that value is added to the overall enthalpy change, since the phase change is endothermic and therefore positive. The bond enthalpy for the formation of C3H6Br2...

Angela G 2K

Delta U is the change in internal energy due to the transfer of energy as work and/or heat. Delta U = q + w

Angela G 2K

The negative sign is there because the internal energy of the system decreases when the system expands, since the system is doing work against the outside pressure and is losing energy. As such, work is negative for expansion (work being done BY the system), and positive for compression (work is bei...

Angela G 2K

An irreversible process in expansion work is defined as one where external pressure differs from internal pressure by a finite, measurable amount. In a reversible process, the external pressure equals the internal pressure, so it could go either way with an infinitesimally small change.

Angela G 2K

Molar heat capacity is the amount of heat needed to raise one mole of a substance by one degree Kelvin, and is dependent on the intermolecular forces between the particles. For example, a substance with strong intermolecular forces (such as water, which has hydrogen bonds) would have a higher heat c...

Angela G 2K

Heat is not a state function because of this equation: q + w = U, where U is the internal energy of the system, q is the heat, and w is the work. Work is not a state function since it depends on the distance an object is moved, or the path, and so therefore the heat must also depend on the path.

CHEMISTRY COMMUNITY

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Re: Calculating activation energy from Arrhenius equation

Re: 15.109

Re: 15.49

Re: Units of K based on the order

15.63 units and reaction order

15.101(a) Overall Reaction

Re: Unique Rate [ENDORSED]

Re: Half Life

Re: How to tell difference btwn thermo and kinetics [ENDORSED]

Re: 14.15 Parts b and c [ENDORSED]

Re: 14.15a

14.117

Re: Why is the change in total entropy zero for a reversible free expansion?

Re: PV = nRT

Re: Practice Midterm #2C

Re: Anode and cathode

Re: Cv,m vs Cp,m vs R

Re: E and G

Re: What does it mean for a reaction to be "thermodynamically favored?"

Re: Why does an exothermic process lead to an increase in entropy?

Re: Residual Entropy [ENDORSED]

Re: reversible and irreversible reactions

Re: Formation of Snow in Clouds [ENDORSED]

Re: Ch. 9 Problems, 5

Re: Bond Enthalpies

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Re: Irreversible vs Reversible

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Re: Heat and state function