## Search found 30 matches

Tue Mar 13, 2018 10:58 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.63
Replies: 6
Views: 312

### Re: 15.63

I had the same question, I'm wondering how they were able to derive that from the arrhenius equation
Tue Mar 13, 2018 9:28 pm
Forum: First Order Reactions
Topic: The integrated rate laws
Replies: 3
Views: 362

### Re: The integrated rate laws

Just use the integrated rate laws that he gives on the equation sheet!
Tue Mar 13, 2018 9:27 pm
Forum: Zero Order Reactions
Topic: Applications
Replies: 2
Views: 320

### Re: Applications

For zero order, that just means that the concentration of that reactant does not affect the rate of the reaction. That can be seen in the problems where you compare the concentrations and rate constants of different reactions to find their orders; if it is zero order, then changing the concentration...
Tue Mar 13, 2018 9:25 pm
Forum: First Order Reactions
Topic: k' in Pseudo-First-Order Rate Laws
Replies: 4
Views: 945

### Re: k' in Pseudo-First-Order Rate Laws

Yes, k prime if the reverse reaction's rate constant. You can use that and the forward reaction's k to figure out the equilibrium constant, K.
Tue Mar 06, 2018 8:47 pm
Forum: General Rate Laws
Topic: Proper units
Replies: 7
Views: 503

### Re: Proper units

For problems 17 and 19, it is confusing to know which units to use, but you should probably keep it consistent with what they give you unless you need to convert (eg. seconds to hours).
Tue Mar 06, 2018 8:44 pm
Forum: General Rate Laws
Topic: Coefficients
Replies: 6
Views: 402

### Re: Coefficients

Coefficients do not determine the order of the reaction, they just matter when it says the concentration of the products vs reactants and you have to multiply by a coefficient to keep the rate consistent.
Tue Mar 06, 2018 8:43 pm
Forum: General Rate Laws
Topic: Units in 15.17 vs. 15.19
Replies: 2
Views: 198

### Re: Units in 15.17 vs. 15.19

I would just keep the units of the answer the same units that they give you, I know that sometimes they change the units interchangeably from minutes and seconds and as long as the answers are consistent with each other I believe its ok.
Thu Mar 01, 2018 10:05 am
Forum: General Rate Laws
Topic: half life vs rate
Replies: 2
Views: 212

### Re: half life vs rate

Like they said, a half life is the time it takes for half of the concentration of the specific reaction to deplete by 50%, and the rate is just how fast it depletes throughout the reaction.
Thu Mar 01, 2018 10:04 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Graphs in Lecture
Replies: 2
Views: 216

### Re: Graphs in Lecture

It depends which order you are talking about. For a first order reaction, the linear graph is the graph of ln[A] vs time, and the curved graph is just concentration vs time.
Thu Mar 01, 2018 10:02 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Overall order
Replies: 4
Views: 439

### Re: Overall order

You just add up each order of the reactants to find total order.
Wed Feb 21, 2018 2:26 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Q & K?
Replies: 4
Views: 311

### Re: Q & K?

In the problems that they are giving in the homework, they are treating Q as if it was K, and using that value to determine whether the reactants or products are favored. In other words, they usually will not give you a K value to compare it to.
Wed Feb 21, 2018 2:25 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst equation usage
Replies: 3
Views: 304

### Re: Nernst equation usage

Yes, you use it under nonstandard conditions, such as a change in the molarities (not 1M like you said), a different temperature, pressure, etc.
Wed Feb 21, 2018 2:23 pm
Forum: Balancing Redox Reactions
Topic: Defining Cathodes and Anodes through standard cell potential
Replies: 2
Views: 209

### Re: Defining Cathodes and Anodes through standard cell potential

Yes you can do it like that, but not all the time. In an electrolytic cell, the potential is supposed to be negative; so, if you did it like you said, then you would mix them up because you are solving for the standard potential to be negative. It is a more safe bet to look at the overall reaction a...
Wed Feb 21, 2018 2:21 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: calculating n
Replies: 9
Views: 613

### Re: calculating n

You can look at the overall reaction, and split it into 2 half reactions. For example, if one of the half reactions for the total equation is Cr3+ + 1e- -----> Cr2+, then here one electron is being transferred. However, if there are 2Cr3+ and Cr2+, then you know there are 2 electrons transferred bec...
Wed Feb 21, 2018 2:18 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Gold ring example
Replies: 1
Views: 89

### Re: Gold ring example

They just took the Hydrogen off of the NO3-, then Nitrogen is reduced from 5+ charge to 2+ charge in NO.
Sun Feb 11, 2018 1:32 pm
Forum: Environment, Fossil Fuels, Alternative Fuels
Topic: fossil fuels on midterm [ENDORSED]
Replies: 2
Views: 845

### fossil fuels on midterm[ENDORSED]

What would be an example in this category that would be on the midterm?
Sun Feb 11, 2018 1:29 pm
Forum: Balancing Redox Reactions
Topic: cat/anions
Replies: 2
Views: 188

### cat/anions

Are the ions that flow from the cathode to the anode through the salt bridge cations or anions?
Sun Feb 11, 2018 1:25 pm
Forum: Phase Changes & Related Calculations
Topic: Environmental impact?
Replies: 6
Views: 613

### Re: Environmental impact?

I would assume that the question he would ask would have to do with a temperature raise in the atmosphere (like how we use q=-q) but I doubt it will be covered on the exam.
Mon Jan 29, 2018 7:42 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Pressure and Volume on Spontaneity
Replies: 2
Views: 305

### Re: Pressure and Volume on Spontaneity

Yes, you have to take into account the different ways that you can solve for deltaS. Since deltaG is the spontaneity of a reaction, it depends on S so it also depends on pressure and volume.
Mon Jan 29, 2018 7:39 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy [ENDORSED]
Replies: 6
Views: 827

### Gibbs Free Energy[ENDORSED]

If deltaS is the disorder (for use of a better word) or a reaction, how is that different than delta G?
Mon Jan 29, 2018 7:37 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneity of a reaction
Replies: 2
Views: 194

### Re: Spontaneity of a reaction

I see what you're saying, and I think that it would be easier to just imagine what would make G negative (stated above). But for some of them, the reverse reaction will be the opposite sign of deltaG, changing whether or not it is spontaneous.
Wed Jan 24, 2018 8:52 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Internal Energy and Enthalpy [ENDORSED]
Replies: 2
Views: 274

### Re: Internal Energy and Enthalpy[ENDORSED]

Along with that, qp=delta H only if the pressure is constant. Therefore, having the work be 0 with a system with constant pressure would result in the only thing changing the internal energy of the system be the change in heat.
Wed Jan 24, 2018 8:50 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Open System
Replies: 7
Views: 790

### Re: Open System

It also depends what kind of system you are trying to increase the q on; you cannot add or remove a substance from a closed system because matter cannot be transferred. However, for a closed system, you can do work on it or change the temperature.
Wed Jan 24, 2018 8:49 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: q isn't a state function
Replies: 3
Views: 380

### Re: q isn't a state function

Q is not a state function because throughout a reaction, the heat changes; therefore, you cannot solve for q with qfinal-qinitial. With work, it is the same thing. The amount of work done on a system is not solved for just by the final and initial work.
Tue Jan 16, 2018 7:24 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Pressure in enthalpy vs heat capacity
Replies: 2
Views: 157

### Re: Pressure in enthalpy vs heat capacity

You always just use what they give you for enthalpies, but heat capacity is definitely more specific. So yes, it does depend on whether the pressure/volume is constant for heat capacity.
Tue Jan 16, 2018 7:22 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Work function
Replies: 4
Views: 184

### Re: Work function

I'm pretty sure it depends on whether work is being done by the system or on the system. I'm assuming if it was being done ON the system, it would be positive and vice versa.
Tue Jan 16, 2018 7:19 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Calculating enthalpy using bond energies [ENDORSED]
Replies: 2
Views: 378

### Re: Calculating enthalpy using bond energies[ENDORSED]

In the textbook, they are only taking into account which specific bonds were broken and produced from the reactants to products. When I do these problems, I tend to write out all of the bonds and multiply by the number of them (it's easier for me), but wither way is fine.
Wed Jan 10, 2018 5:32 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: What is bond enthalpy and can someone explain to me what Lavelle was doing with the Lewis Structures in today's lecture?
Replies: 3
Views: 154

### Re: What is bond enthalpy and can someone explain to me what Lavelle was doing with the Lewis Structures in today's lect

Bond enthalpy is the energy needed to break a bond. In today's lecture, Lavelle was essentially trying to show us which bonds are broken in the specific reaction, and how you use the enthalpies from both the reactants and products to find the total change in enthalpy. Since there were bonds broken a...
Wed Jan 10, 2018 5:27 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heating Curve: How is the kJ calculated?
Replies: 2
Views: 137

### Re: Heating Curve: How is the kJ calculated?

Sometimes you have to convert the units given to you in order to do the calculation correctly. For example, the specific heat capacity and the heat of fusion have different units, so in order to get both of them to kJ, you have to cancel out the units in each equation to be converted to kJ.
Wed Jan 10, 2018 5:25 pm
Forum: Phase Changes & Related Calculations
Topic: Exothermic Rxn
Replies: 6
Views: 500

### Re: Exothermic Rxn

The meaning of an exothermic reaction means that it gives off energy once completed, not that the reactants need to be spontaneous in order to do so.