## Search found 52 matches

Sat Mar 14, 2020 10:01 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysts
Replies: 8
Views: 56

### Re: Catalysts

With heterogenous catalysts we would have to consider the adsorption and change due to the varying physical states of the substance.
Sat Mar 14, 2020 9:58 am
Forum: Reaction Mechanisms, Reaction Profiles
Replies: 2
Views: 49

I believe that we were told by Dr. Lavelle to not use the steady state method and instead use the pre-equilibrium method that he taught us in class. The pre equil method involves looking at the rate laws of the intermediate reactions and seeing whether or not those rate laws match up with the given ...
Sat Mar 14, 2020 9:56 am
Forum: Zero Order Reactions
Topic: All reactants zero order?
Replies: 7
Views: 109

### Re: All reactants zero order?

If the catalyst was saturated with just reactants, then the catalyst would be the main driving force of the reaction and it would only be dependent on reaction rate, or k, in a zeroth order reaction. This would be possible in a real life reaction if the catalyst was saturated completely and the conc...
Sat Mar 14, 2020 9:49 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: kinetics vs. thermodynamics
Replies: 7
Views: 74

### Re: kinetics vs. thermodynamics

Thermodynamics is focused on the transfer of heat or energy in a reaction, focusing primarily on the beginning and ends of the state of a reaction while kinetics is focused on the actual speed of the process taken to get to that reaction.
Sat Mar 14, 2020 9:47 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Outline 6 Learning Objective
Replies: 3
Views: 83

### Re: Outline 6 Learning Objective

You can look at the rate of change of one species and how that is related to another by looking at the unique rate law which takes into account the actual stoichiometric coefficients and tells you each unique rate.
Sat Mar 14, 2020 9:46 am
Forum: General Rate Laws
Topic: Elementary reactions
Replies: 4
Views: 70

### Re: Elementary reactions

As said earlier, an elementary reaction is simply breaking down the reaction into a series of intermediate reaction steps which can be combined in order to write the rate law. The benefit of writing out elementary reactions is that the reaction that occurs in the slow step is the rate-determining st...
Sun Mar 08, 2020 5:45 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Units
Replies: 2
Views: 33

### Re: Units

The units of k is determined by the rate of the reaction and the order of the reaction determines the units for K.
Sun Mar 08, 2020 5:42 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Forward and Reverse Rates
Replies: 1
Views: 21

### Re: Forward and Reverse Rates

I believe with equilibrium to determine whether or not the concentration was negated out of the equilibrium expression the lower bound limit was 10^-3 and could possibly be 10^3 for the upper bound limit although I'm not sure if it would be the same for kinetics.
Sun Mar 08, 2020 5:41 pm
Forum: Zero Order Reactions
Topic: Zero Order reaction rate constant
Replies: 8
Views: 63

### Re: Zero Order reaction rate constant

The rate constant, regardless of the order of the reaction will not be dependent on the coefficients of the reaction.
Sun Mar 08, 2020 5:39 pm
Forum: General Rate Laws
Topic: slow step
Replies: 4
Views: 63

### Re: slow step

For the slow step the actual reaction that determines which step is the slow step is the intermediate reaction right before the slow step.
Sun Mar 08, 2020 5:32 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: thermo or kinetics?
Replies: 9
Views: 136

### Re: thermo or kinetics?

For kinetics you should be looking at how the reaction is progressing by looking at the rates and the actual pathway of the reaction. For thermodynamics you should be looking at the initial and final rates and making sure you understand the energies involved with both of them.
Sun Mar 08, 2020 5:31 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: order of reactions
Replies: 7
Views: 102

### Re: order of reactions

The order of a reaction explains how that reaction rate varies depending on how the reaction is organized. For example if it was a zeroth order reaction then there would be no correlation between reaction rate and time and first order would have a direct correlation and so on.
Sun Mar 01, 2020 8:08 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Equations
Replies: 2
Views: 52

### Re: Equations

I would focus on making sure you understand what concept is being relayed by each equation and what variables are required and that should give you a better way to memorize.
Sun Mar 01, 2020 8:05 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 6N15.
Replies: 2
Views: 57

### Re: 6N15.

I don't think it is a coincidence because there is the same species in both cells so it would make sense to assume a concentration cell.
Sun Mar 01, 2020 7:58 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 6M.7 Strength as Reducing Agent
Replies: 3
Views: 54

### Re: 6M.7 Strength as Reducing Agent

I believe you should not just be looking at standard reduction potentials when comparing metals, but rather where they are located on the periodic table. If elements are near the bottom left they are good reducing agents as they are metals that want to lose electrons whereas if you look at the top l...
Sun Mar 01, 2020 7:56 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: delta G=-nFE
Replies: 7
Views: 117

### Re: delta G=-nFE

If the n is not given, look at the half reactions and find the number of moles of electrons transferred and that is your n value because that is what n stands for in the equation.
Sun Mar 01, 2020 7:54 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: cell diagrams
Replies: 8
Views: 80

### Re: cell diagrams

It depends on the half reactions and whether or not that is considered an anode or a cathode reaction as at the anode there is oxidation and at the cathode there is reduction but the main reason anodes are written on the left and cathodes on the right is to stay consistent with the cell diagram nota...
Sun Feb 23, 2020 7:38 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Negative E
Replies: 3
Views: 23

### Re: Negative E

When a reaction is spontaneous and the delta G is negative that means that free energy is available and not required in order for the forward reaction to occur.
Sun Feb 23, 2020 7:30 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L.5 b)
Replies: 5
Views: 43

### Re: 6L.5 b)

Platinum would be included as an anode because it is used as a salt bridge in the galvanic cell in order to rebalance the respective charges of the solutions and allow the transfer of electrons to proceed.
Sun Feb 23, 2020 7:28 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cells
Replies: 3
Views: 39

### Re: Galvanic Cells

The importance of a galvanic cell is that charge is being transferred from one species to another, or from anode to cathode and as electrons are transferred from one species to another there is a buildup of charge and a voltage associated with that. Therefore electricity is generated when electrons ...
Sun Feb 23, 2020 7:25 pm
Forum: Balancing Redox Reactions
Topic: Figuring Out Electrons Transferred for a Problem Where Both Sides Have The Same Oxidation Number
Replies: 3
Views: 38

### Re: Figuring Out Electrons Transferred for a Problem Where Both Sides Have The Same Oxidation Number

With species that have the same oxidation number you have to make sure to balance the reaction with waters and adding in ions or electrons in order to create a balanced half reaction. Once that is done you can settle your balanced reaction.
Sun Feb 23, 2020 7:22 pm
Forum: Balancing Redox Reactions
Topic: 6K.1
Replies: 6
Views: 62

### Re: 6K.1

When you're looking at oxidation and reduction think about whether that species will be gaining or losing electrons and depending on what is happening that will be the agent. In terms of balancing redox reactions you have to add species like H20 or H+ or OH- depending on the solution type.
Fri Feb 14, 2020 10:13 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Pizza Rolls 3E
Replies: 4
Views: 73

### Re: Pizza Rolls 3E

The first part of the statement, that removing heat from a system will be exothermic is true because heat is leaving the system. However as said before phase changes play a role in not changing temperature because heat can be added to go from one phase to the next but not change the temperature in a...
Fri Feb 14, 2020 10:08 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Delta S
Replies: 4
Views: 55

### Re: Delta S

In a reversible system the entropy of the system and the surroundings are equal and opposite to each other making the net entropy zero because the change in one aspect (the system) will be matched by changes in its surroundings to make sure the pressure internal and external are approximately equal ...
Fri Feb 14, 2020 10:06 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G
Replies: 6
Views: 59

### Re: Delta G

The Delta G with the degree sign is the one being calculated because this is under standard conditions for the reaction and correlates to a standard enthalpy and entropy and is calculated that way.
Fri Feb 14, 2020 10:04 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Differences
Replies: 5
Views: 153

### Re: Differences

Outside of what differences have already been distinguished, an isolated system is where the change in internal energy is equal to zero because the amount of work the system is doing or being done on is equal to the replacement of heat by the surroundings. Thus when q and w are equal there is no cha...
Fri Feb 14, 2020 10:02 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Bomb Calorimeter
Replies: 5
Views: 130

### Re: Bomb Calorimeter

I'm not sure about the specific problem that Lavelle went over in class where the work and heat would be equal to zero during combustion, but according to the textbook a bomb calorimeter is NOT an isolated system but a closed system. This is because even though it doesn't exchange matter with the sy...
Sun Feb 09, 2020 11:31 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4D.7
Replies: 5
Views: 49

### Re: 4D.7

I would first look at pV=nRT for to solve for the temperature if all of that info is given but if not then I would just go with standard conditions at 298 K.
Sun Feb 09, 2020 11:26 pm
Forum: Gibbs Free Energy Concepts and Calculations
Replies: 3
Views: 34

For free expansion there is no work being done because it is done in a vacuum state and thus it is zero for work.
Sun Feb 09, 2020 11:08 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy calculations (rev and irrev)
Replies: 2
Views: 41

### Re: Entropy calculations (rev and irrev)

I believe you should not think about the equations as when to memorize when to use them but think about the process itself and what is changing versus staying the same like in reversible the temperature isn't changing so therefore you can't use the temperature change equation but for volume that wou...
Sun Feb 09, 2020 11:03 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Comparing entropy change
Replies: 2
Views: 35

### Re: Comparing entropy change

When looking at entropy change if it is negative then the reaction is is moving toward order and fewer micro-states whereas with a positive entropy there are more micro states and a higher entropy.
Sun Feb 09, 2020 10:56 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: deltaU=deltaH= negative
Replies: 2
Views: 28

### Re: deltaU=deltaH= negative

When the internal energy is equal to the negative change in enthalpy this means that it is a exothermic reaction and the products are releasing heat and are being favored.
Sun Feb 02, 2020 10:30 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond enthalpy calculations
Replies: 4
Views: 36

### Bond enthalpy calculations

In terms of calculation is it helpful to draw out diagrams to tell which bonds are being created and being formed, What’s the best way to approach these type of problems?
Sun Feb 02, 2020 10:28 pm
Forum: Phase Changes & Related Calculations
Topic: Equipartition Theorum
Replies: 2
Views: 39

### Re: Equipartition Theorum

I think you just have to understand how they relate to the heat capacities of reactions depending on constant volume or pressure.
Sun Feb 02, 2020 10:26 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat capacities of different compounds
Replies: 3
Views: 25

### Heat capacities of different compounds

When looking at compounds such as NO and NO2 how do you tell between which one will have a larger heat capacity? Does this have to do with the type of bonding occurring in the compound or size? Or something else entirely?
Sun Feb 02, 2020 10:23 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: thermochemistry equations
Replies: 5
Views: 43

### Re: thermochemistry equations

I would start from understanding the underlying concepts behind heat, work, enthalpy and how one concept relates to another and that will help you form those equations and prevent you from stressing about it!
Sun Feb 02, 2020 10:18 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Constant volume vs constant pressure
Replies: 1
Views: 9

### Constant volume vs constant pressure

Why is it that when a reaction is at constant volume the measurement of enthalpy is the change in internal energy versus when the reaction is at constant pressure the enthalpy is the same as heat transfer?
Sun Jan 26, 2020 4:29 pm
Forum: Phase Changes & Related Calculations
Topic: State Properties
Replies: 4
Views: 43

### Re: State Properties

A state property can be described with something like enthalpy, which describes the ending and the starting states but there is no relevance of the process of how fast the reactant makes the product.
Sun Jan 26, 2020 4:20 pm
Forum: Phase Changes & Related Calculations
Topic: Combustion vs. Cellular Respiration
Replies: 5
Views: 66

### Re: Combustion vs. Cellular Respiration

The enthalpy of the reaction for glucose in a combustion reaction versus one with cellular respiration is completely dependent on what the other reactants it is interacting with and the relative bond energies of those reactants and products.
Sun Jan 26, 2020 4:16 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Calculating enthalpy change with phase changes
Replies: 3
Views: 26

### Re: Calculating enthalpy change with phase changes

When Dr. Lavelle was talking about phase changes, he was saying that in the standard state all substances should be a gaseous phase so if some of your reactants are in a liquid or solid phase you have to factor in an extra heat of vaporization or an extra enthalpy value in order to account for the p...
Sun Jan 26, 2020 4:11 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: standard state
Replies: 2
Views: 25

### Re: standard state

Another thing for method 3 is that when you are calculating the change in enthalpy you have to make sure your equation is balanced and all your substances are in their standard states.
Sun Jan 26, 2020 4:08 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpies
Replies: 3
Views: 28

### Re: Enthalpies

The difference between standard reaction enthalpy and standard enthalpy of formation is that the standard enthalpy of formation is for a substance in its standard state (or in the element's most stable form) whereas standard reaction enthalpy by itself doesn't specific the phase of the substance.
Sun Jan 19, 2020 4:34 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Conjugate Seesaw
Replies: 5
Views: 40

### Re: Conjugate Seesaw

In addition to what has already been said, it also means that if there is a stronger acid there will be a weaker conjugate base to accompany it and this is especially relevant in the example with water. With water the acidic and basic components have to balance off of each other in order to maintain...
Sun Jan 19, 2020 4:32 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 5% rule
Replies: 10
Views: 109

### Re: 5% rule

The 5% rule is used normally in indicating if when setting up the Kc expression if x should be factored into the concentration of the initial reactant. You normally approximate without using that x and if the resulting value x/(initial conc) is less than 5% it is valid to not factor that x in the co...
Sun Jan 19, 2020 4:27 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Reaction Shifts Left or Right
Replies: 15
Views: 170

### Re: Reaction Shifts Left or Right

When looking at an expression you should first determine if it is an endothermic or exothermic reaction and depending on that you can determine how the reaction shifts. When looking at how heat moves around we know that endothermic reactions require heat in the forward direction, and the opposite wo...
Sun Jan 19, 2020 4:21 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Test 1 Acids and Bases Topic
Replies: 9
Views: 90

### Re: Test 1 Acids and Bases Topic

For the acids and bases, do we have to memorize the list of strong acids and bases for future tests and exams?
Sun Jan 19, 2020 4:16 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Percent Protonation
Replies: 2
Views: 32

### Percent Protonation

When calculating percent protonation, do you calculate the concentration of hydronium/hydroxide ions divided by the concentration of the acid/base or is it the concentration of the conjugate base divided by the concentration of the acid/base?
Sun Jan 12, 2020 2:01 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Situations in which Q=K
Replies: 7
Views: 59

### Situations in which Q=K

What reactions describe when Q=K or is a reaction even present when there is the same amount of product and reactant?
Sun Jan 12, 2020 2:00 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Partial Pressures
Replies: 4
Views: 41

### Re: Partial Pressures

For total partial pressures, they are normally calculated when factoring in all of the different contributions to the pressure of the gas and only then is the total used in the ICE table for equilibrium.
Sun Jan 12, 2020 1:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Pure substances in reactions
Replies: 2
Views: 25

### Re: Pure substances in reactions

I don't believe that you can combine two solids together or pure liquids together because based on their properties there might just be a mixture formed as there is not an actual chemical change in either reactant to produce the product. This is why looking at aqueous solutions or gases is important...
Sun Jan 12, 2020 1:11 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium and Limiting Reagent
Replies: 2
Views: 23

### Re: Equilibrium and Limiting Reagent

When we were talking about limiting reagents, we were not looking necessarily at reactions at equilibrium and we had to find the reactant that would limit the use of the other reactants for the reaction to proceed. This relates to equilibrium because once you find the limiting factor you can ensure ...
Sun Jan 12, 2020 1:05 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Factors Affecting K
Replies: 5
Views: 59

### Re: Factors Affecting K

The only external factors that impact K would be temperature because that can impact how much of the reactant is produced or product is created as well. Other factors such as the change in pressure or volume would not affect the K value because the system would adjust concentrations of products and ...