CHEMISTRY COMMUNITY

Rafsan Rana 1A

The commas are used just because they the two molecules are in the same phase, but other than that, the molecule is being reduced.

Rafsan Rana 1A

Also, hydrogen electrodes need an inert metal such as platinum.

Rafsan Rana 1A

Is it safe to assume the hydrogen cell will be the anode because when calculating E cell standard, any positive number minus 0 will give a postive voltage?

Rafsan Rana 1A

Flipping the anode identifies it as an oxidation reaction and allows us to cancels out the electrons with the cathode side when writing the equation.

Rafsan Rana 1A

When using the equation delta g = -nFe, e cell doesn't change and G does because of the n which is number of electrons transferred. Doubling the equation means increasing the number of electrons changing the value of G.

Rafsan Rana 1A

Yes, and also make sure you write out the chemical reaction to find out which are the products and the reactants. Q = products/reactants.

Rafsan Rana 1A

In addition, if you look at the equation for it, mass isn't accounted for anywhere.

Rafsan Rana 1A

How does changing concentration of reactants or products in a reaction effect E cell?

Rafsan Rana 1A

If we have two molecules that are both solid, do we still have to use Pt or any other inert metal since they are in the same phase.

Rafsan Rana 1A

Also remember, when writing the cell diagram to add Pt or any other inert metal.

Rafsan Rana 1A

They are the same. The difference comes when comparing them to electrolytic cell. A galvanic cell transforms chemical energy into electrical energy. An electrolytic cell converts electrical energy into chemical energy.

Rafsan Rana 1A

To the question : "Do you always add the H2O at opposite ends of where you have added OH or H+?"

You should be adding the h20 first and then adding OH or the H to the opposite side to balance the number of hydrogens.

Rafsan Rana 1A

I believe the side that has less hydrogens is the side you would add the OH because the purpose of adding it is to balance the number of hydrogen and this is only in basic solutions

Rafsan Rana 1A

To add on, the reducing agent is basically the molecules getting oxidized because it releases the electron that is added and reducing the other molecule. In the same sense, the oxidizing agent is the molecules getting reduced.

Rafsan Rana 1A

In addition to the answers given, the reason we want to have a positive E cell is because it leads to a negative standard gibbs free energy which in turn means a positive value for entropy meaning the process is spontaneous.

Rafsan Rana 1A

In the anode, usually the reverse of the given half reactions is occuring, because oxidation has to take place in the anode, right?

Rafsan Rana 1A

Also, pt is used when dealing with hydrogen, and when two of the molecules are in the same phase such as both are aqueous solutions.

Rafsan Rana 1A

I think making of the reaction concentration smaller conceptually simulates the reactant not having as much of an affect on reaction rate allowing us to see kind of affect the other reactant has.

Rafsan Rana 1A

When enzyme is saturated, the increase in reaction rate levels off.

Rafsan Rana 1A

zero order reaction occurs at a constant rate. First order reaction rate is dependent on a reactant concentration and second order reaction rate is dependent on the square of a concentration of reactant.

Rafsan Rana 1A

What is relationship between the half life of the second order reaction and the concentration of the reactant?

Rafsan Rana 1A

It gives the concentration of reactants or products at anytime after the start of the reaction.

Rafsan Rana 1A

for 6L.3 part e, the for the half reaction in the anode the solutions manual says
Sn4+ + 2e- --> Sn2+, but the book problem doesn't show Sn2+, just Sn2 so aren't we supposed to assume it is two molecules of Sn instead a charge of 2+ so the balanced equation should be 2Sn4+ + 8e- -->Sn2?

Rafsan Rana 1A

They are related through the equation deltaG = -nF(deltaE). G is Gibbs free energy, n is number of electrons transferred, F is faraday constant, and e is cell potential. If cell potential is negative then reaction is spontaneous and if it is positive then reaction is non spontaneous.

Rafsan Rana 1A

To add on, the electrode at which the electrons enter and “add to” the cell is the cathode while the electrode at which the electrons leave the cell is the anode.

Rafsan Rana 1A

The degree symbol indicates standard conditions for the process while without the degrees indicates whatever conditions the reaction is given in.

Rafsan Rana 1A

In a reaction, the reducing agent is the one that is oxidized and the oxidizing agent is the one that is reduced, right?

Rafsan Rana 1A

They are the same. The difference is between electrochemical cells and galvanic cells. I believe electrochemical cells convert electrical energy into chemical energy while galvanic cells convert chemical energy into electrical energy.

Rafsan Rana 1A

Isn't the equation G = Gnot + RTlnQ ?

Rafsan Rana 1A

The Vant Hoff equation can also be manipulated and use to calculate K at a different temperature if delta H is known.

Rafsan Rana 1A

I think there should still be separation of the half reactions as long there is a method for the transport of ions or electrons

Rafsan Rana 1A

Can someone explain what is meant by potential difference?

Rafsan Rana 1A

for 5G.15 I keep getting -2.7 kj per mol but the answer says -27 kj per mol. Can someone tell me what I'm doing wrong is the answer key wrong.

Rafsan Rana 1A

Irreversible processes are usually spontaneous and quick where as irreversible processes are slow and maintain equilibrium throughout the entirety of the process. However, I believe it will be clearly stated or inferred in any test.

Rafsan Rana 1A

Yes, positional entropy is a result of change in volume, for example where a gas expands in a larger volume, while residual entropy is I believe a result of dipole dipole interactions.

Rafsan Rana 1A

To add on, when Gibbs free energy is negative that means that according the equation for gibbs free energy, delta S or change in entropy is positive and if change in entropy is positive, it means that a process is spontaneous.

Rafsan Rana 1A

I forgot what Dr. Lavelle said in lecture, but it was something about delta H or the change in enthalpy doesn't change even if temperature changes? Can someone explain exactly what he said and what it means?

Rafsan Rana 1A

The equation is used to find out the change in the equilibrium constant, K, of a chemical reaction with the change in temperature and standard enthalpy change.

Rafsan Rana 1A

When w is negative, it means that the system is doing work, while when w is positive, it means that the system is having work done on it.

Rafsan Rana 1A

Is enthalpy change for a reverse reaction the negative of the enthalpy change for the forward reaction?

Rafsan Rana 1A

If the volume stayed constant, could change in enthalpy still be equal to heat added?

Rafsan Rana 1A

Gases can change volume depending on pressure but solids and liquids maintain a constant volume.

Rafsan Rana 1A

Also, irreversible processes almost always do more work than reversible processes.

Rafsan Rana 1A

A system is considered isolated when the system cannot exchange energy/heat with its surroundings. An example would be a boiling water in a closed insulated container, like a hydroflask. This is considered an isolated system because the hot water in the container cannot exchange heat/energy with the...

Rafsan Rana 1A

So heat isn't a state function but internal energy of an isolated system is a state function. What qualifies something to be, or not to be, a state function?

Rafsan Rana 1A

Exothermic is negative because it is releasing energy, while endothermic is positive because it is absorbing energy

Rafsan Rana 1A

You should use certain methods based on the information you are given, so different methods for different circumstances, but also I believe that the methods using bond enthalpies is the least accurate method because the bond enthalpies of non-diatomic molecules are averages from many different molec...

Rafsan Rana 1A

If I remember correctly, using the strategy with the bond enthalpies is the least accurate method so there is a benefit to using the other two.

Rafsan Rana 1A

I forgot to write it in my notes, but which of the three methods was supposed to be the least accurate?

Rafsan Rana 1A

OH- are the conjugate base of water. However, if water reacts with an acid, wouldn't it act as a base thus it would have a conjugate acid of hydronium ions?

Rafsan Rana 1A

pKa = -log Ka; so according to that equation, the lower the pKa is, the higher the Ka will be meaning it is a stronger acid. The higher the pKa is, the lower the Ka will be meaning it will be a weaker acid.

Rafsan Rana 1A

So for problem 5H.2, the book says that for the reaction, K = 2.5 * 10^10, however in the solutions manual they use K = 2.5 * 10^7 for the calculations. Can someone please explain? Am I missing something here?

Rafsan Rana 1A

It is homogeneous when the products and reactants are in the same phase. Heterogeneous is when the all the products and reactants aren't in the same phase so you would have to omit pure liquids and solids in your equilibrium calculations.

Rafsan Rana 1A

pure liquids and solids, which includes water, are disregarded for the equilibrium expression because they don't have an affect on reactant amount at equilibrium and they don't have a concentrations to be used to calculate k.

Rafsan Rana 1A

When you look at the ideal gas , pv=nrt, the numbers have to be constant, so if p is being doubled v has to be halved since they are being multiplied to balance out and keep the value of nrt constant.

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