CHEMISTRY COMMUNITY

Noe BM 1J

Is the rate always going to depend on the reactant with smallest concentration? A pseudo rate is considered when there are too many changing concentrations. For instance, it is difficult to calculate the rate when you have k[A][B], and both A and B are changing. As such, you make one significantly l...

Noe BM 1J

Yes, since the slow step determines the rate of the overall reaction, it means that the order of the slow step is the same as the order of the reaction.

Noe BM 1J

Because the slowest step needs to be done for the reaction to be able to be completed.

Noe BM 1J

As far as I know, we never include products in the rate law, correct? A first-order reaction means that there is one reactant or molecule present in the rate law. A second-order rate law either has two of the same reactant (rate law would be squared) or two different ones (they would be multiplied b...

Noe BM 1J

How would we know the order of the reaction if we are given an integrated rate law?

asannajust_1J wrote:the total order of the reaction is the sum of the exponential coefficients. This can be determined based on graphs, a given rate law, or an integrated rate law.

Noe BM 1J

Why does increasing the concentration of reactants in a zero-order reaction not affect the reaction rate?

Noe BM 1J

I think you only use the concentration of the reactants when calculating the rate (this is for differential rate laws).

Noe BM 1J

Could anyone please explain what exactly is an intermediate species?

Noe BM 1J

Thank you! I see how it is related and it's definitely useful. Could you elaborate a little more on how it's an indirect way to measure enthalpy, please? When using the Van't Hoff equation, we assume that the difference in enthalpy is considered to be the same, and we assume that the difference in e...

Noe BM 1J

If the concentration of one reactant is small and the concentration of the other reactant(s) is large, the reaction rate will depend on the reactant with small concentration, so the reaction is easier to study.

Noe BM 1J

When do you add platinum to the cell diagram of a redox reaction, and on which side does it go?

Noe BM 1J

What is the difference between a redox reaction in acidic solution and one in a basic solution?

Noe BM 1J

The anode loses electrons (undergoes oxidation) and the cathode gains electrons (undergoes reduction).

Noe BM 1J

Why is the oxidizing agent being reduced and not oxidized?

Charysa Santos 4G wrote:An oxidizing agent refers to the item being reduced, which allows for the other species to be oxidized. A reducing agent is exactly the opposite: it is being oxidized in order for another species to be reduced.

Noe BM 1J

It will be until the end of electrochemistry; thus, kinetics should not be included.

WYacob_2C wrote:
CynthiaLy4F wrote:I believe it will only cover topics from the midterm up until the end of kinetics.

Would it be up until the end of kinetics or the end of electrochemistry?

Noe BM 1J

Is it in number of moles?

Bryce Barbee wrote:N is found by finding how many electrons are being transferred in the process.

Noe BM 1J

For the first part of your answer, this means that the reaction will not occur spontaneously in the forward reaction, right? A negative cell voltage -- reaction will occur spontaneously but in the opposite direction as compared to the forward. A positive cell voltage--reaction will occur spontaneous...

Noe BM 1J

Is the flow of electrons always going to be form anode to cathode or are there circumstances where it's the other way around?

Noe BM 1J

Could you elaborate a little more on how it's an indirect way to measure enthalpy, please? When using the Van't Hoff equation, we assume that the difference in enthalpy is considered to be the same, and we assume that the difference in entropy between reactants and products is also the same at these...

Noe BM 1J

Could anyone please send me a copy of their notes from 02/14/2020, I would really appreciate it. My email is noebamen02@g.ucla.edu. Thanks in advance!

Noe BM 1J

When delta G is negative, it's spontaneous. When delta G is positive.

Noe BM 1J

I think such numbers like that one will always be given to us.

Noe BM 1J

Yes, a spontaneous reaction has a negative delta G.

LBacker_2E wrote:Is this related to the relationship between ∆G and the direction of a spontaneous reaction? Does a spontaneous reaction have a -∆G and proceed in the forward direction?

Noe BM 1J

It won't change unless standard conditions are changed

Noe BM 1J

Under which conditions would you use delta S = nRln(V2/V1) and delta S = qrev/T?

Noe BM 1J

Can someone please explain how a negative delta G makes a reaction favorable?

005324438 wrote:Yes exactly, when ΔG is negative the reaction is favorable, and when it is positive it is unfavorable.

Noe BM 1J

Yes, you exclude solids and liquids. You only take into account gases and aqueous solutions when calculating Q and/or K.

Noe BM 1J

This is because there's no expansion since pressure and volume are constant, right?

Elena Bell 1C wrote:If a system is a constant pressure and volume then w would equal zero. Since, deltaU=q+w and q=deltaH I think it would just be deltaU=deltaH if both pressure and volume is constant.

Noe BM 1J

I was about to ask the same question since homework problems specify whether it's reversible or irreversible, so I didn't know if we have to know based on the given information. This is kind of irrelevant to the question but will the question always say if it is reversible or irreversible? Or is the...

Noe BM 1J

Are there any homework problems where we have to use the integral instead of the simplified formula? We use -p(delta)v when the pressure is constant, because it allows us to factor out the variable P from the integral to end up with just integrating the constant "1", which simplifies the i...

Noe BM 1J

Because it uses the average of many molecules.

Noe BM 1J

It might also be helpful to think that the heat of a system plus the heat of its surroundings has to be equal to 0. So, if you have an exothermic reaction that released -X amount of heat, the surroundings gained +X amount of heat in order for the addition of both to be 0.

Noe BM 1J

Does anyone know if we need to know the integral equation for reversible reaction or just the simplified version? Honestly that is the biggest difference, and because of the difference there are two different equations that can be used. For irreversible reactions, use the equation w=-P(change in V) ...

Noe BM 1J

Does this means that if I have H2 and want to form H2O, then there would be an enthalpy of formation? Diatomic molecules such as H2, O2, N2, F2, I2, CL2, and Br2 all have an enthalpy of formation of 0 because it is their naturally occuring state. There is no enthalpy of formation for the way somethi...

Noe BM 1J

I think it's just the first one, which is also the best method to use.

Noe BM 1J

An exothermic reaction has a negative H value because it releases energy when bonds are being formed. An endothermic reaction has a positive H value because it needs energy in order to break bonds.

Noe BM 1J

They should be given to us since we didn't go over how to calculate it.

Noe BM 1J

Does this mean that Specific heat capacity will always be less than molar heat capacity since it's 1 gram vs. 1 mole? Molar heat capacity is the amount of heat needed to raise the temperature of one mole of a pure substance by one degree Kelvin. Specific heat capacity is the amount of heat necessary...

Noe BM 1J

Does anyone know if we will be asked on the test whether a reaction is exothermic or endothermic? If so, will the delta H value be given to us?

Noe BM 1J

If delta H is negative, it means that the reaction is exothermic (it releases energy). If delta H is positive, the reaction is endothermic (it requires energy).

Noe BM 1J

I think the question would state which units you need to use. If not, pay attention to the units of pressure. For example, if you are given the pressure in order to find the volume, you should use the R constant that has the same units as pressure in order for them to cancel out each other.

Noe BM 1J

Yes, they are. When you decrease a volume molecules have less space to move around, so they collide more--increasing the pressure. When you increase the volume molecules have more space and therefore, collide less--decreasing the pressure.

Noe BM 1J

The x value is so small that when you subtract it from .10 it doesn't make a big chante to it, so you can ignore it. When you ignore it, it becomes easier to solve for x because you would now have Ka = x^2/.10

Noe BM 1J

This definitely makes sense!!! Thanks. The way I explain it to myself is that these stoichiometric coefficients are just telling us more than one of these species was formed. For example, in the balanced chemical equation to form water, 2H2 + O2 <-> 2H2O, the equation is telling us that two H2O spec...

Noe BM 1J

How do you know whether to use the concentration or pressure of a gas when doing ICE tables? Also, if I use the pressure of a gas, what units do I use?

Noe BM 1J

You only take into account the gases, that's why when compressing the system there's no effect on the equilibrium since there is the same amount of moles of gas on both sides of the reaction.

Noe BM 1J

Does anyone know the reason as to why the coefficients in a reaction become the exponents of the concentration values?

Noe BM 1J

The way I think about it is that if you remove SO3, NO will increase because it has to make up for the SO3 that's being removed in order for the reaction to be at equilibrium.

Noe BM 1J

Remember that this equation can be rewritten as P=nRT/V, and n/V is the same as concentration. So, P=concentration times RT.

P: Pressure
V: Volume in liters
n: number of moles
R: Ideal gas constant
T: Temperature in Kelvin

Noe BM 1J

Kc is the equilibrium constant when using concentrations and Kp is for when using pressures.

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