CHEMISTRY COMMUNITY

Samantha Kan 2L

Constant volume does mean that delta V is equal to 0. Since a bomb calorimeter is an isolated system, Delta U is equal to 0 because no heat or work is being transferred/done.

Samantha Kan 2L

The standard hydrogen electrode is the cathode or the anode depending on what else is in the system (like copper or zinc). How you can tell whether the standard hydrogen electrode is the cathode or anode is based on the cell potential. The cell potential should be positive, so according to the equat...

Samantha Kan 2L

Since it is at the same temperature, you know that Delta U is equal to zero. However, you also know that work is happening because the balloon is expanding, therefore indicating a change in volume. According to Delta U = q + w, for Delta U to be zero, there must also be heat being transferred in ord...

Samantha Kan 2L

You find the concentration of A used up, which is stoichiometry since you're given the concentration of B that rises. Then you subtract the concentration of A used up from the initial concentration of A for the final concentration. After that, since it's a first order reaction you use the equation l...

Samantha Kan 2L

I think for this class, we consider the initial concentration of the reactant when finding the rate law because it is easier to study when there is little product formed.

Samantha Kan 2L

You are using the equation ln[A] = -kt + ln[A]0 to find k. However, first you must use stoichiometry to find the concentration of A used up to form the given mols of B. Then you subtract the concentration of A used up from the initial concentration of A to find the final concentration of A. After yo...

Samantha Kan 2L

Will we ever have to figure out whether a step in a reaction is fast, very fast, or slow? Or is that always given to us? Also, is it possible to have two slow steps in a reaction?

Samantha Kan 2L

Will we be expected to do calculation problems regarding pseudo-first-order reactions? If so, what are some examples of what we might need to know?

Samantha Kan 2L

You need the final mols of A, but you are given the concentration B has risen to. You first calculate the amount of mols of A that need to be used up for B to have that concentration. Then you subtract that value from the initial mols of A to find the final mols of A.

Samantha Kan 2L

You use E(cathode)-E(anode) to find the standard E. If E is positive, it favors the products so k>1.

Samantha Kan 2L

You add 5e- because you need to balance out the charge. Since the left side is Mn7+ and the right side is Mn2+, you need 5 electrons to make the charges on both sides equal. You know it is Mn7+ because oxygen has a 2- charge, so O4 should have an 8- charge. However, MnO4 only has a 1- charge overall...

Samantha Kan 2L

You add platinum when there is no solid metal to conduct the electron flow in the galvanic cell.

Samantha Kan 2L

I think you should use delta S = nCvln(T2/T1), with n as the total mols of gas and then add your answer from part a) to get the total entropy. However, I don't know if we can assume that the gases are ideal, since it doesn't say so in the problem. If they aren't, then we can't calculate Cv.

Samantha Kan 2L

For 6a), the reaction is exothermic, so delta H is negative. We are also given that the temperature is very low. Based on the equation delta G = delta H - T(delta S), if delta S is positive, then the reaction is spontaneous since the answer will be negative. Even if delta S is negative, since the te...

Samantha Kan 2L

In the book, it usually has delta S as the entropy of the system, while it specifies the entropy of the surroundings and total entropy with delta Ssurr and delta Stot respectively. Delta Stot would therefore be delta S + delta Ssurr.

Samantha Kan 2L

For this question, you don't need Q because the problem is assuming the reactants and products are at equilibrium. To find the standard Gibbs free energy, you just have to use the equation delta G = -RTlnK. Hope this helps!

Samantha Kan 2L

Is there always a salt bridge? If not, when would a salt bridge be used?

Samantha Kan 2L

In terms of balancing, when the reaction takes place in a basic solution you use OH- to balance the chemical reaction. When the reaction takes place in an acidic solution, you use H+ to balance.

Samantha Kan 2L

Yes, pressure and volume do affect the spontaneity of a reaction because they contribute to entropy. For example, when a system is expanding, there is more area and translational energy. This results in a higher entropy.

Samantha Kan 2L

There is no relationship between reversibility and spontaneity of a reaction. It depends on entropy and Gibbs free energy.

Samantha Kan 2L

Degeneracy refers to the number of different states energy can be contained in. The more states (higher degeneracy), the higher the entropy, because there is more randomness.

Samantha Kan 2L

For this problem they are finding the volume of the coal in cm^3 and using the given density to find the grams of carbon burned. Since the delta H given is in kJ/mol, you need to convert the grams of carbon burned to the mols of carbon burned, which is why they have the (12.01 g/mol) in the equation...

Samantha Kan 2L

An exothermic reaction means that heat is being released from the system into the surroundings, which in this case would be the reactor. Since heat is being released, the reactor temperature will increase. Therefore, to maintain a constant temperature in the reactor, it will need to be cooled. Hope ...

Samantha Kan 2L

For homework problem 9.1, you can use the equation Delta S = q/T to calculate the change in entropy. Just make sure to keep your units constant.

Samantha Kan 2L

The book mentions the concept of free expansion, and I understand that w=0. What would be an example of free expansion? Would we ever encounter a problem with free expansion in this class?

Samantha Kan 2L

The number +717 kJ/mol is given in the problem itself, and it is the standard enthalpy of sublimation of carbon. Since it is given to us directly in the problem, I don't think it is in the tables or the appendix.

Samantha Kan 2L

Typically a higher bond enthalpy means that it takes more energy to break/form the bond. Stronger bonds therefore have higher enthalpies.

Samantha Kan 2L

Is the symbol for enthalpy of freezing -∆Hfus or is there another symbol we should use?

Samantha Kan 2L

Are standard reaction enthalpies always molar enthalpies? Also, I am a bit confused on the term "standard state" and what that implies.

Samantha Kan 2L

I understand that a change in enthalpy of a system takes into consideration heat released or absorbed at constant pressure. However, is there a relation between enthalpy and volume of the system?

CHEMISTRY COMMUNITY

Search found 30 matches

Re: Bomb Calorimeter

Re: Standard Hydrogen Electrode

Re: Test 1 #3

Re: Question 15.23

Re: Rate Laws

Re: 15.29

Step Speed

Pseudo-First-Order Reactions [ENDORSED]

Re: 15.23 & 15.29 [ENDORSED]

Re: 14.31

Re: 14.3

Re: Platinum

Re: Practice Midterm Karen Leung #8 [ENDORSED]

Re: practice test 6A&6B

Re: entropy

Re: 11.21

Salt Bridge

Re: Basic vs. Acidic

Re: Pressure and Volume on Spontaneity

Re: What is the relationship between reversibility and spontaneity of a reaction?

Re: Degeneracy and Entropy

Re: 109

Re: Exothermic Reactions

Re: Calculating Entropy for Irreversible Energy Transfers [ENDORSED]

Free Expansion

Re: 8.67b

Re: Enthalpy Trends

Enthalpy of Freezing

Standard Reaction Enthalpies [ENDORSED]

Enthalpy and Volume of a System