## Search found 29 matches

Sat Mar 16, 2019 9:40 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction rate
Replies: 1
Views: 268

### Reaction rate

Is there an easy way to tell which reaction is fast and which is slow in a a series of reactions if we are not told in advance? Are there any tell-tale signs that give it away?
Sat Mar 16, 2019 9:35 pm
Forum: First Order Reactions
Topic: Half-Lives
Replies: 4
Views: 348

### Half-Lives

Are we suppose to ignore the half-life formulas for zero-order and second-order reactions? The textbook mentioned that we only ever really use the half-life equation of a first-order reaction, but all three formulas are on our formula sheet.
Sat Mar 16, 2019 9:12 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: net rate of reaction
Replies: 1
Views: 302

### net rate of reaction

Is there a defined equation we use to find the net rate of reaction for a series of elementary reactions? I can't find one on our formula sheet. Or does it have to be deduced one reaction at a time? I'm just having a hard time connecting the dots between all the reactions.
Sat Mar 16, 2019 8:32 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Frequency factor
Replies: 2
Views: 118

### Re: Frequency factor

The frequency factor is also known as the pre-exponential factor, A. It's a constant that can be derived experimentally, describing the number of times two molecules collide.
Sat Mar 16, 2019 8:23 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: k(1)/k(-1)
Replies: 4
Views: 340

### k(1)/k(-1)

What does k(1)/k(-1) mean? Why do we use it in our rate law? Mostly I just can't conceptualize what it means or how we find k(-1).
Fri Mar 15, 2019 8:37 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Ecell
Replies: 4
Views: 184

### Ecell

How can the Ecell of a reaction be found by both adding the Ecells of its half reactions, like Dr. Lavelle did during the review on Friday, as well as subtracting the Anode Ecell from the Cathode Ecell? Both ways seem fundamentally opposite, but yet give you the same answer. Do you change the signs ...
Fri Mar 15, 2019 6:42 pm
Forum: General Rate Laws
Topic: Rate Law
Replies: 1
Views: 103

### Rate Law

Does every reaction have a rate of formation and combustion? Or can certain rates be ignored? I feel like I've seen a problem with a reaction that didn't end up giving a rate of combustion, just formation.
Fri Mar 15, 2019 12:32 pm
Forum: Student Social/Study Group
Topic: class pictures
Replies: 15
Views: 2911

### Re: class pictures

Thanks for the help. Here you go:
Fri Mar 15, 2019 10:50 am
Forum: Student Social/Study Group
Topic: class pictures
Replies: 15
Views: 2911

### Re: class pictures

How do you post pictures? I have a decent one from up front, but I don’t know how to post it.
Thu Mar 14, 2019 6:00 pm
Forum: First Order Reactions
Topic: Doubling Concentrations
Replies: 3
Views: 138

### Doubling Concentrations

Does doubling concentrations double the order of a reaction or does it just increase the order by 1?
Thu Mar 14, 2019 4:07 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Log vs ln
Replies: 2
Views: 118

### Re: Log vs ln

The conversion is only done when using the second Nernst equation, however both equations mean the same thing so there is no need to convert in between them once you choose the one you are going to use.
Thu Mar 14, 2019 4:03 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Log vs Ln
Replies: 2
Views: 124

### Re: Log vs Ln

I'm not exactly sure how everything cancels out exactly, but I believe I can confirm from the book that there are some simplifications that can be done in order for log(Q) to be used rather than ln(Q) at the end of the equation.
Thu Mar 14, 2019 4:00 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation
Replies: 1
Views: 100

### Nernst Equation

When using the Nernst equation for concentration how does finding Q help us find the concentration we are looking for?
Wed Mar 13, 2019 6:23 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram Order
Replies: 2
Views: 113

### Cell Diagram Order

Can someone explain the order of a cell diagram better than the textbook? It's very confusing because the books states that the anode and cathode can be interchanged on the right depending on the sign if the Ecell, yet only reductions occur on the right. Earlier the text also says that the cathode i...
Wed Mar 13, 2019 6:16 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode and Cathode
Replies: 14
Views: 330

### Anode and Cathode

How can you figure out which side of the cell diagram will be the cathode and which will be the anode? Is it only based on the whether the Ecell is negative or positive along, or are there other factors?
Tue Mar 12, 2019 7:49 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: $$\Delta U = \Delta H$$
Replies: 2
Views: 401

### $$\Delta U = \Delta H$$

I'm just a little confused when you're suppose to disregard that $\Delta U = \Delta H$ and instead use the equation $\Delta H = \Delta U + \Delta n_{gas}RT$ instead? What are the conditions that need to be met?
Tue Mar 12, 2019 7:44 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heat of combustion
Replies: 1
Views: 85

### Re: Heat of combustion

You can solve this problem by just adding the \Delta H_{c} s correctly. In this problem all you would need to do is change -1560kJ to +1560kJ because C_{2}H_{6} is the product in this reaction. You also need to multiply -286kJ by 2 because there are two moles of H_{2} . The -1300kJ of C_{2}H_{2} doe...
Tue Mar 12, 2019 6:19 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity at Constant Volume and Pressure
Replies: 2
Views: 266

### Heat Capacity at Constant Volume and Pressure

I'm having a hard time distinguishing which constants to use in the correct situations. When do we use $\frac{3}{2}R$R, $\frac{5}{2}R$, $\frac{7}{2}R$, 3R, and 4R? Are there certain ones we can ignore because they never come up, or could we be asked to use any of them on our exam?
Tue Mar 12, 2019 2:49 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: internal energy
Replies: 3
Views: 155

### Re: internal energy

Shouldn't it be only isothermal, reversible reactions that have a \Delta U = 0, not irreversible? I'm just confused because example 8.5 in the book says the same about reversible, opposed to irreversible. Edit: Actually the example puts both a reversible and irreversible reactions \Delta U = 0, so I...
Tue Mar 12, 2019 2:21 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4D7 temperature
Replies: 2
Views: 119

### Re: 4D7 temperature

If I'm not mistaken the standard temperature for these reactions is $25^{\circ}$ Celsius, which converts to the $298^{\circ}$ Kelvin used to solve the problem.
Mon Mar 11, 2019 5:49 pm
Forum: Ideal Gases
Topic: Cell Diagram/Ecell
Replies: 8
Views: 494

### Re: Cell Diagram/Ecell

Is there a difference between what is being oxidized/reduced and the oxidizing/reducing agent? I always get confused when I see one or the other in problems. In actuality do oxidizing agents get reduced and reducing agents get oxidized?
Mon Mar 11, 2019 5:29 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Finding heat(q)
Replies: 3
Views: 131

### Finding heat(q)

Are all the equations used to find \mathit{q} , such as \mathit{q}=C\Delta T , \mathit{q}= mC_{s}\Delta T , and \mathit{q}= nC_{s}\Delta T all just used interchangeably depending on the information provided or there certain cases where one will give you a better, or maybe more accurate answer than t...
Mon Mar 11, 2019 5:22 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: ICE
Replies: 19
Views: 607

### Re: ICE

E is what you are always looking to find, as it stands for Equilibrium concentration. So that line will tell you the concentrations of both your reactants and products individually as their reach their most stable state at equilibrium.
Mon Mar 11, 2019 5:06 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ka2
Replies: 1
Views: 81

### Re: Ka2

I believe Ka2 is used when an acid has more than one dissociation, meaning that donates a 2nd $H^{+}$
Therefore it will have more than one dissociation constant.
Mon Mar 11, 2019 2:47 pm
Forum: Ideal Gases
Topic: 5% rule
Replies: 12
Views: 1706

### Re: 5% rule

After reading this entire thread I've somehow only become even more confused. How can you divide the (initial condition-x)/(initial condition), if we are looking for x in the first place. There is no change in value, its still the same initial amount being divided by the initial amount, except now t...
Sun Mar 10, 2019 4:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Self-Test 11.11A in textbook 6th Edition
Replies: 1
Views: 109

### Self-Test 11.11A in textbook 6th Edition

Bromine monochloride, BrCl, decomposes into bromine and chlorine and reaches the equilibrium 2BrCl(g)\leftrightharpoons Br^{_{2}}+Cl_{2} , for which K = 32 at 500. K. If initially pure BrCl is present at a concentration of 3.30 mbar, what is its partial pressure in the mixture at equilibrium...
Sun Mar 10, 2019 4:10 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equation I've never seen before?
Replies: 3
Views: 125

### Equation I've never seen before?

Are we ever going to be asked to use the equation $P_{J}=\mathit{n_{J}}RT/V$?
It keeps being brought up in the examples in the book and just ends up being confusing because I don't remember if its ever been on any of our exams.
Sat Mar 09, 2019 6:56 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Negligible X
Replies: 3
Views: 120

### Negligible X

What is the rule that can be applied when using an ice table that states you can ignore certain x values? I remember reading that it has to be less than 5% of the K value given, but always get confused when it comes to applying that rule. Something to do with 10^(-3)? Clarification would help out tr...
Thu Feb 28, 2019 7:43 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Reaction Order
Replies: 3
Views: 151

### Cell Reaction Order

When combining half reactions you obtained from a cell diagram does it matter which side the reactants are on and which side the products are? More specifically, as long as all electrons get crossed out does the order or anything else of the final cell reaction matter? It feels like it shouldn't, bu...