## Search found 56 matches

Fri Mar 13, 2020 8:12 pm
Forum: Reaction Mechanisms, Reaction Profiles
Replies: 2
Views: 28

Will we only be expected to find the rate-determining step using the pre-equilibrium method, or will we be expected to use steady state as well? If the latter is the case, how can one distinguish whether to use the pre-equilibrium or steady state method in a given situation?
Fri Mar 13, 2020 7:49 pm
Forum: *Enzyme Kinetics
Topic: How to distinguish the intermediates and catalysts?
Replies: 8
Views: 134

### Re: How to distinguish the intermediates and catalysts?

While an intermediate is produced then consumed, a catalyst is consumed then regenerated.
Fri Mar 13, 2020 7:46 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow Step Determination
Replies: 5
Views: 100

### Re: Slow Step Determination

You will sometimes be given the slow step, but if not, you can use the equilibrium constants and equivalent ratios for each step in order to substitute values in to this step's rate law. When the rate law, which now includes these substituted values, matches with the overall rate law, then the rate-...
Fri Mar 13, 2020 11:29 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Using kJ/mol vs. kJ
Replies: 2
Views: 113

### Using kJ/mol vs. kJ

Do we only use kJ/mol if we have been given the value or calculated a reaction with only one mole of a particular reactant?
Wed Mar 11, 2020 2:17 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Units for Thermo Calculations
Replies: 2
Views: 108

### Units for Thermo Calculations

How do you know whether to use the units kJ/mol or J/mol in thermodynamic calculations?
Wed Mar 11, 2020 12:22 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Determining the Change in Entropy of the Surroundings without Being Given the Reversibility
Replies: 2
Views: 83

### Determining the Change in Entropy of the Surroundings without Being Given the Reversibility

In the homework problem 4I.3, the chanfe in the entropy of the surroundings is asked for, however it does not specify whether the process was reversible or irreversible. Will this information be specified if asked for on the final?
Sun Mar 08, 2020 10:20 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Intermediate Species
Replies: 9
Views: 127

### Re: Intermediate Species

Many reactions are thought to occur in steps, as they make the formation of particular products from particular products more plausible. An intermediate is a molecule, atom, or ion that is produced in one of these stepwise reactions and consumed in another one of these stepwise reactions.
Sun Mar 08, 2020 10:18 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysts
Replies: 8
Views: 92

### Re: Catalysts

Proper orientation also helps increase the reaction rate.
Sun Mar 08, 2020 10:16 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysts
Replies: 8
Views: 92

### Re: Catalysts

I am not exactly sure about a non-enzymatic catalyst's mechanism of lowering activation energy, but the principles of the two types of catalysts performing the process is likely similar. In an enzyme, the various chemical groups on the amino acids that are exposed to the substrate form non-covalent ...
Sun Mar 08, 2020 10:02 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Temperature
Replies: 4
Views: 38

### Re: Temperature

Larger temperatures can supply more heat energy to the reactions, bringing their measured energy closer to the activation energy required for the reaction to proceed.
Sun Mar 08, 2020 9:58 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: A
Replies: 8
Views: 55

### Re: A

In the Arrhenius equation, A does not represent concentrations. Instead, it is a reaction-based constant that describes the spatial requirements for the reaction to occur. If k is large, meaning that the reaction rate will be large, then A will also be large. A large A tells us that the spatial requ...
Sun Mar 08, 2020 9:54 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: molecularity
Replies: 5
Views: 32

### Re: molecularity

Yes, as once you get past termolecular, the odds of that number of molecules colliding becomes extremely slim. Even termolecular reactions are rare and often occur at low rates.
Sun Mar 01, 2020 4:20 pm
Forum: Zero Order Reactions
Topic: Order of Reactions
Replies: 4
Views: 92

### Order of Reactions

What determines whether a reaction is zero, first, or second order? I would assume that it would be molar ratios but I've seen exceptions to this so I was wondering what the explanation is.
Sun Mar 01, 2020 2:04 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: Rate of consumption
Replies: 3
Views: 333

### Re: Rate of consumption

Rate of consumption is the rate at which the moles of reactant is decreasing and rate of product formation is the rate at which product is being formed. The rate of the reaction is represented as 1/a(-d[R]/dt), which is equal to k[R]^n.
Sun Mar 01, 2020 1:58 am
Forum: General Rate Laws
Topic: Rate Constant Units
Replies: 3
Views: 91

### Re: Rate Constant Units

The rate constant k is different based on the order of reaction. Because Rate = k{R}^n, the units of the [R]^n portion of the equation will change based on the order. Despite this change in the mechanism of the reaction, the units for Rate must remain as M/s, as this is what the rate is. Therefore, ...
Thu Feb 27, 2020 10:19 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Acid/Base Concentration Cells
Replies: 1
Views: 42

### Acid/Base Concentration Cells

A question in the book asks what range (in volts) does a voltmeter need to have to measure pH in the range of 1 to 14 at 25 °C if the voltage is zero when pH = 7? I'm having trouble understanding how acid/base equilibria represents a concentration cell and how I would use equations like Nernst in th...
Thu Feb 27, 2020 9:11 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electrolyte
Replies: 4
Views: 45

### Electrolyte

What is meant by the term electrolyte? I've seen it in a lot of electrolysis problems in the book but never saw the definition in the context of electrolysis.
Thu Feb 27, 2020 9:01 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cells [ENDORSED]
Replies: 3
Views: 129

### Re: Concentration Cells[ENDORSED]

Can you post your steps? In a neuron (a nerve cell), the concentration of K+ ions inside the cell is about 20–30 times as great as that outside. What potential difference between the inside and the outside of the cell would you expect to measure if the difference is due only to the imbalance of pot...
Thu Feb 27, 2020 2:30 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cells [ENDORSED]
Replies: 3
Views: 129

### Concentration Cells[ENDORSED]

In the problem 6.61, the potential difference is asked for when the concentration inside a neuron is 20x-30x greater than outside a neuron. I tried to use the Nerst equation so the I could plug in the given Q but got around 0.03 V when the answer was 0.09 V. Anyone know what I'm doing wrong?
Sun Feb 23, 2020 8:17 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation for Concentration Cells
Replies: 2
Views: 45

### Nernst Equation for Concentration Cells

For 6N.3, the solutions manual said that E(cell) = +0.067 V, but I got -0.067V due to the Nernst equation, as E^o(cell) was equal to zero, meaning that E(cell) = -(RT/nF)lnQ. Can someone explain where I am going wrong?
Sun Feb 23, 2020 4:26 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: movement e
Replies: 3
Views: 30

### Re: movement e

The electrons move in order to reach their lowest point of free energy, meaning that if there is a release of free energy with the redox reaction, it will be spontaneous. This is why dG and E can be connected through Faraday's constant and the number of moles of electrons. The electrons move through...
Sun Feb 23, 2020 2:05 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

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

For the problem O3 (aq) + Br- (aq) -> O2 (g) + BrO3- (aq), you are supposed to split into the oxidation and reduction half reactions. The half reaction of the species with bromine is pretty clearly the oxidation half reaction, but I was curious about how the reduction reaction happens between O3 (aq...
Sat Feb 22, 2020 5:36 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Cell Potentials
Replies: 2
Views: 29

### Standard Cell Potentials

When standard cell potentials are used, they are calculated with the reduction potentials of the cathode an anode half reactions with the equation E(cell) = E(cathode) - E(anode), correct? Did anyone else see a different, possibly incorrect answer on the solutions manual for question 6M.1?
Sat Feb 22, 2020 5:03 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Cell Potentials
Replies: 4
Views: 50

### Standard Cell Potentials

When calculating a standard cell potential, do you subtract the potential on the right from the potential on the left or subtract the potential of the cathode from the potential of the anode?
Sat Feb 22, 2020 1:46 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Vant Hoff Equation vs dG = -RTln(K)
Replies: 1
Views: 61

### Vant Hoff Equation vs dG = -RTln(K)

Before doing problem 5.55, I was under the impression that when you had a temperature that wasn't 298.15 K, you used the Vant Hoff Equation to determine the equilibrium constant since it accounts for the effect that a temperature change has on Kc. But in 5.55 the dG = -RTln(K) was used. What is the ...
Sun Feb 16, 2020 4:20 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: maximum work
Replies: 5
Views: 116

### Re: maximum work

Yes, maximum work is a theoretical expression. In actuality, you will likely have both a change in work and heat over the course of the reaction, as dU = q + w. Expressing the change in Gibbs free energy as maximum work is just a simpler way to describe it.
Tue Feb 11, 2020 10:00 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy of the System for irreversible expansions
Replies: 7
Views: 187

### Re: Entropy of the System for irreversible expansions

Yes, they are the same because entropy is a state function.
Tue Feb 11, 2020 9:59 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy Change over the Course of Thermodynamic Processes
Replies: 3
Views: 43

### Entropy Change over the Course of Thermodynamic Processes

In the pizza roll problem on the isobaric, isochoric, and isothermal process, the answer for the total change in entropy was stated to be zero. However, I calculated a different answer by adding the changes in entropies at each step. Does anyone know why the answer is zero?
Tue Feb 11, 2020 11:52 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 1
Views: 33

### Bond Enthalpies

A question on the pizza rolls review packet asked to find the change in enthalpy for the reaction C6H12O6 + 6O2 = 6H2O + 6CO2 using bond enthalpies. Will we be expected to know the structures of common organic molecules like glucose for the midterm?
Sun Feb 09, 2020 9:21 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cp v.Cv
Replies: 6
Views: 64

### Re: Cp v.Cv

You will be told whether a reaction is occurring at constant pressure or volume, and based on that you use the corresponding specific heat. This specific heat will be greater for constant pressure, as more heat energy is required to raise the temperature due to the fact that some of this heat energy...
Sun Feb 09, 2020 8:29 pm
Forum: Calculating Work of Expansion
Topic: Reversible vs Irreversible
Replies: 3
Views: 53

### Re: Reversible vs Irreversible

They should specify if the process is reversible or irreversible, as you do use different equations. For calculating work, you would use w = P(delta V) for an irreversible expansion and w = nRTln(V2/V1) for a reversible expansion.
Sun Feb 09, 2020 6:39 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: Going from delta S to delta H
Replies: 2
Views: 48

### Re: Going from delta S to delta H

If you knew delta S of the surroundings and the temperature at which this process is occurring, you could calculate delta H with the equation delta S (surroundings) = - delta H/T
Sat Feb 08, 2020 5:17 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Evaluating the Stability of a Process
Replies: 2
Views: 58

### Evaluating the Stability of a Process

In one of the homework problems, a question asks whether or not the decomposition of various into their elements or more basic molecules will occur. One of these molecules that could potentially decompose is HCN. What would this decomposition reaction look like?
Sat Feb 08, 2020 1:37 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Total Entropy Change
Replies: 2
Views: 26

### Re: Total Entropy Change

But wouldn't there had to have been a positive change in entropy for that process to occur spontaneously?
Sat Feb 08, 2020 12:42 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Total Entropy Change
Replies: 2
Views: 26

### Total Entropy Change

In some of the homework problems I have done so far, the entropy change of the surroundings was asked for after the entropy change of the system was calculated. The answer was always the same magnitude of the entropy change of the system with an opposite sign. This would mean that the total entropy ...
Sun Feb 02, 2020 8:24 pm
Forum: Calculating Work of Expansion
Topic: Expansion
Replies: 4
Views: 51

### Re: Expansion

Work of expansion occurs when the gas is doing work on an object(s), such as a piston, and work of compression occurs when an object(s) is doing work on the gas. Work of expansion has a negative sign and work of compression has a positive sign.
Sun Feb 02, 2020 8:16 pm
Forum: Calculating Work of Expansion
Topic: Change in Pressure vs Constant Pressure
Replies: 1
Views: 19

### Re: Change in Pressure vs Constant Pressure

Yes. If you are only given one measurement of pressure and not asked to solve for another, you can assume that pressure is constant.
Sun Feb 02, 2020 8:14 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: U
Replies: 4
Views: 47

### Re: U

Internal energy is the energy within a system. You can solve for the change of internal energy with the equation dU = dH + PdV. In this equation, where d stands for delta, dH represents the change in heat energy of the system while PdV represents the work either done on the system or done by the sys...
Sun Feb 02, 2020 6:09 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Types of Systems
Replies: 3
Views: 56

### Re: Types of Systems

I'm not sure whether or not we will be told what type of system the system in a problem is, but the important things to remember are that open systems allow for a transfer of matter and energy, closed systems allow for a transfer of energy, and isolated systems allow for a transfer of neither. Anoth...
Sun Feb 02, 2020 5:59 pm
Forum: Calculating Work of Expansion
Topic: 4C.13
Replies: 2
Views: 33

### Re: 4C.13

You solve this problem by setting up a heat transfer equation, q(ice) = -q(water). Because no phase change occurs with the water, q simply equals mC(dT). But for the ice, a phase change does occur. Because of this situation, q(ice) is composed of both the enthalpy of fusion and the mC(dT) equation. ...
Sun Jan 26, 2020 10:42 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Transfer
Replies: 2
Views: 101

### Heat Transfer

Does anyone know how to answer question 4A.9? I tried setting the q equations equal to each other to get the final tempertaure but my final temperature was lower than both the starting temperatures, which doesn't make sense. Thanks!
Fri Jan 24, 2020 12:36 am
Forum: Phase Changes & Related Calculations
Topic: Steam vs. Boiling Water
Replies: 10
Views: 136

### Re: Steam vs. Boiling Water

This concept has to do with the intermolecular forces between water molecules. Because of hydrogen bonding between water molecules, water at 100 C has to have a significant amount of energy placed into it in order to overcome these interactions and vaporize into steam. This large energy requirement ...
Fri Jan 24, 2020 12:23 am
Forum: Phase Changes & Related Calculations
Topic: symbol of Heat
Replies: 3
Views: 53

### Re: symbol of Heat

H can be viewed as a system's enthalpy, or its total internal energy. While this energy often takes the form of heat, this is not always the case. It can apply to other forms of energy as well. Since H represents energy, delta H represents the change in this energy over the course of a chemical reac...
Fri Jan 24, 2020 12:04 am
Forum: Phase Changes & Related Calculations
Topic: Heat Capacity
Replies: 2
Views: 24

### Re: Heat Capacity

The two types of heat capacity are specific heat capacity and molar heat capacity. Both can can used to calculate q, however the variables in each of these equations change slightly to account for the different units each form of heat capacity uses. Whereas q=mCdT for specific heat capacity, q=nCdT ...
Thu Jan 23, 2020 2:22 am
Forum: Phase Changes & Related Calculations
Topic: Enthalpy of vaporization
Replies: 2
Views: 44

### Re: Enthalpy of vaporization

Vaporization has such a large enthalpy because of the number of intermolecular interactions that must be broken in order for a gaseous state to be achieved. While melting only requires some intermolecular interactions to be broken, vaporization requires almost all intermolecular interactions be brok...
Thu Jan 23, 2020 2:17 am
Forum: Phase Changes & Related Calculations
Topic: State Property
Replies: 6
Views: 67

### Re: State Property

A state property is a measurement that is not dependent on the path that was taken to get there. In a chemical reaction, there is a certain activation energy that must be achieved for the reaction to proceed. This activation energy is the highest point of energy for the entire reaction, but it is no...
Thu Jan 16, 2020 8:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: H3O+
Replies: 4
Views: 29

### Re: H3O+

We use H3O+ because it describes the state of the dissociated H+ ions. After dissociating, H+ ions, or protons, create a covalent bond with one of oxygen's two lone pairs and, as a result, form a hydronium ion.
Thu Jan 16, 2020 8:21 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Endothermic and exothermic
Replies: 5
Views: 76

### Re: Endothermic and exothermic

It's possible to infer whether the reaction is exothermic or endothermic without knowing the exact delta H. Because bond formation releases energy, a reaction that forms bonds is exothermic. On the other hand, a reaction that forms bonds is endothermic, as this process requires energy.
Thu Jan 16, 2020 8:06 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Replies: 11
Views: 101

### Re: ICE and quadratic formula

The ICE table can be calculated without using the quadratic formula when K is less than 10^-3. When K is less than 10^-3, one can reason that the change in concentration of the reactant, which has it's new concentration represented in the denominator, is insignificant and cross the x representing th...
Thu Jan 16, 2020 7:52 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Inert Gas
Replies: 7
Views: 81

### Re: Inert Gas

A gas is inert if it does not react. Only a few gases, such as neon, are inert, as these gases must have a full valence shell that prevents them from forming bonds. This lack of reactivity allows for inert gases to be placed in a container where a reaction in equilibrium is occurring and not effect ...
Thu Jan 16, 2020 7:39 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Change in pressure effect on reactions
Replies: 3
Views: 28

### Re: Change in pressure effect on reactions

When the pressure is changed through an increase or decrease in volume, the concentrations of the reactants and products change with it. This change in concentrations, either seen in a deficiency in products relative to reactants or reactants relative to products, causes the reaction to shift to a p...
Thu Jan 09, 2020 8:09 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Exercise 5I.15
Replies: 3
Views: 42

### Re: Exercise 5I.15

This problem requires you to set up an ICE box. Since NH4HS is solid, it is not included in the ICE box. However, it still reacts to produce H2S and more NH3 in addition to the 0.2 M of NH3 that was present before the reaction began. One you have added this unknown, additional amount of product to t...
Thu Jan 09, 2020 7:56 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ratios of Pressure
Replies: 2
Views: 29

### Re: Ratios of Pressure

As long as K is set up correctly by taking into account the stoichiometric coefficients of the reactants and products, the value produced will be equal among these two reactions, as a reaction occurring at a single temperature has a consistent equilibrium constant.
Thu Jan 09, 2020 7:44 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Temperatures and Equilibrium
Replies: 4
Views: 47

### Temperatures and Equilibrium

Are there multiple temperatures where a reaction can reach equilibrium or is there a set equilibrium temperature for a specific reaction?
Tue Jan 07, 2020 12:10 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Effect of High Initial Concentration of Reactant
Replies: 5
Views: 80

### Effect of High Initial Concentration of Reactant

If one has a larger concentration of reactants than usual, the equilibrium concentration of products can be expected to be higher than usual as well, correct?
Tue Jan 07, 2020 11:50 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Effects of Concentration on Equilibrium
Replies: 6
Views: 79

### Effects of Concentration on Equilibrium

If the concentration of a product or reactant is changed while a reaction is in equilibrium, will the reaction then be temporarily shifted out of equilibrium?