CHEMISTRY COMMUNITY

Kevin Tabibian 1A

Why is the Gibbs free energy change of water boiling at 100 celsius equal to zero?

Kevin Tabibian 1A

Question 14.97 is Use the data in Appendix 2B and the fact that, for the half-reaction F2(g) + 2 H^(+)(aq) + 2e -> S 2 HF(aq), E standard =3.03 V, to calculate the value of Ka for HF.How are we supposed to determine which half-reaction is the anode and which is the cathode? I don't understand why we...

Kevin Tabibian 1A

In question 14.41 part be you are given the concentration cell of H2, why is n=1 if the half reactions are are H2+2e -> 2H+. Shouldn't the n=2?

Kevin Tabibian 1A

why is the Cl ion not included in the overall reaction, nor is it written as an intermediate in the solution manual. What happened to the Cl ion?

Kevin Tabibian 1A

For part d of question 14.13, where you are asked to write the half reactions of (d) Au(+) → Au + Au(3+), how do we know that one of the half-reactions is Au → Au(3+) + 3e instead of Au(+) → Au(3+) + 2e. I assumed that both half reactions would begin with Au(+), how should I have known that one was ...

Kevin Tabibian 1A

If the reduction potential of Fe (2+) in [Fe (2+) + 2e → Fe] is -.44, does that mean that the reduction potential of Fe is positive .44. Or will the reduction potential of Fe also be -.44?

Kevin Tabibian 1A

Because E is not a state function.

Kevin Tabibian 1A

It depends on the entropy equation that is being used.

Kevin Tabibian 1A

Residual entropy is essentially the disorder of a molecule, near absolute zero, that is the result of it's different possible microstates. Whenever a question is given on residual entropy it is usually asking you to measure entropy through the amount of microstates in a molecule(s). I believe that h...

Kevin Tabibian 1A

Are there any textbook problems involving pseudo reactions? I haven't been able to find one in the assigned homework and would like some practice. Any help would be appreciated.

Kevin Tabibian 1A

My TA said it's fair game because it's technically in the section.

Kevin Tabibian 1A

My TA said that it's very likely not relevant to the problems that will be tested.

Kevin Tabibian 1A

Whatever it takes to make k positive

Kevin Tabibian 1A

Because decay is typically a first order reaction

Kevin Tabibian 1A

They both play a role in determining the extent of reactions

Kevin Tabibian 1A

Iron you glad I didn't say copper?

Kevin Tabibian 1A

In question 14.5 the balanced half reaction for O3 (g) --> O2 (g) is H2O (l) + O3 (g) + 2e- --> O2 (g) + 2OH- (aq) . How are we supposed to know that it takes 2 elections to form O2. Where is the number 2 coming from?

Kevin Tabibian 1A

Are we going to be given the periodic table for test 2?

Kevin Tabibian 1A

Oxidizing agents help substances oxidize by being reduced. The opposite is true for reducing agents.

Kevin Tabibian 1A

Yes, but be careful determining whether a question is asking for the change in energy of the system or a reaction within the system. Because all those terms could very well not be equal to zero for to a reaction within an ideal bomb calorimeter. But the total energy of the bomb calorimeter will be u...

Kevin Tabibian 1A

consider the q=mc $\Delta$ T + 0.5(m $\Delta$ H)
m $\Delta$ H is divided by 2 because only half of the ice cream, make sure your answer is in line with the units that the question is asking

Kevin Tabibian 1A

Is it possible to force a reaction that will decrease the entropy of the universe? Or would that defy the second law of thermodynamics

Kevin Tabibian 1A

When Delta =0 it means that neither the formation of products nor reactants will be favored. This relates to our previous understanding of equilibrium from Chem 14 A where we understood that at equilibrium the rate of creation of products and reactants will be stable.

Kevin Tabibian 1A

If I were to dissolve a salt in water by stirring it (let's say NaCl), will I be affecting the entropy of the water that surrounds it

Kevin Tabibian 1A

A negative change in Gibbs free energy means that the product will be spontaneously favoured and therefore more stable

Kevin Tabibian 1A

Why is constant pressure and thermally insulated mentioned in question 9.43 Suppose that 50.0 g of H2O(l) at 20.0 C is mixed with 65.0 g of H2O(l) at 50.0 C at a constant atmospheric pressure in a thermally insulated vessel. Calculate S and Stot for the process. What does having a constant pressur...

Kevin Tabibian 1A

I believe he was just demonstrating that that specific temperature is a threshold. A student asked and professor said that you could also set up an inequality; the final answer would be the same .

Kevin Tabibian 1A

It means that it is energetically favorable and naturally occurring ( spontaneous). This is represented by a negative delta G

Kevin Tabibian 1A

Spontaneous simply means that it can naturally occur without outside influences. It makes sense that because everything in nature attempts to have as low of an energy level as it can, losing free energy ( negative Delta G) will happen naturally

Kevin Tabibian 1A

I like to also think about the fact that equilibrium is measured where the change in G is equal to 0. This also explains why negative G values are spontaneous, because they are approaching a lower number (where dG=0). If there is less free energy it is safe to assume that there is less potential for...

Kevin Tabibian 1A

The integral is an equation that gave origin to several others we derived in class. It was meant to help our comprehension, yet we do not need it in our calculations.

Kevin Tabibian 1A

This signifies that when there are more possible states available that a substance will be more stable (at equilibrium)

Kevin Tabibian 1A

I believe that being at thermodynamic equilibrium (constant heat) is part of the definition of a reversible reaction whereas it is not required for irreversible.

Kevin Tabibian 1A

In thermodynamics we are often calculating for reversible expansion even though professor said that most real life cases are irreversible. Why are we calculating for maximum work if it might be less accurate?

Kevin Tabibian 1A

Does Dr Lavelle post his PowerPoints online? I can't seem to find it

Kevin Tabibian 1A

Work done on a system means that the internal energy of the system will increase, because the surroundings are placing work unto the system.
Work done by a system means that the internal energy of the system will decrease, because the system is placing work unto the surroundings.

Kevin Tabibian 1A

A Bomb Calorimeter is a isolated system, meaning that no heat or work will be exchanged with its surroundings, because q and w are a measure of energy transfer to surroundings it is safe to assume that the change in work and heat will be zero.

Kevin Tabibian 1A

An irreversible process would be as if I took a single 10g weight off of a balloon, allowing it to quickly expand. While a reversible process would be as if I individually removed from a balloon infinitely small weights that all collectively added up to 10g. The work in the second case would be much...

Kevin Tabibian 1A

When considering enthalpy (Δ H=q), is the letter "H" or "ΔH" Enthalpy? Online the definition of enthalpy is given as a measure of the internal heat of a system, but whenever we are talking about enthalpy it has to do with change. Sometime Professor call "ΔH" enthalpy an...

Kevin Tabibian 1A

We generally prefer extensive properties in chemistry because they are more specific. I would guess that your second question depends on the specific chemistry question you're answering.

Kevin Tabibian 1A

You are right to determine that enthalpy is a state function while heat is not. The only reason that they are equivalent in the equation (Δ H=q) is because it is at a constant pressure, mathematically leading allowing for the equation to be derived. Just because they are different types of functions...

Kevin Tabibian 1A

Think about the example Professor gave in class with altitude. Altitude can be measured using a difference of distances, ie subtraction. You can also get altitudes, a state function, by adding two smaller altitudes. Try not to overthink it

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