Search found 34 matches

by Kailey Brodeur 1J
Mon Mar 12, 2018 10:39 am
Forum: Balancing Redox Reactions
Topic: Half-reactions
Replies: 4
Views: 207

Re: Half-reactions

In addition to what was said above, make sure when you add the two half reactions together the electrons cancel out. This helps on the idea of flipping reactions because in one half reaction the electrons must be on the reactant side and in the other half reaction the electrons must be on the produc...
by Kailey Brodeur 1J
Mon Mar 12, 2018 10:36 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Steady State vs. Pre-Equilibrium
Replies: 2
Views: 121

Re: Steady State vs. Pre-Equilibrium

In steady state calculations, there is a constant intermediate concentration in the rate limiting step which differs from the pre equilibrium approach which has a buildup of the intermediate in the fast step (not the determining step) resulting in an equilibrium of the fast step. For the steady stat...
by Kailey Brodeur 1J
Mon Mar 12, 2018 10:26 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediates
Replies: 6
Views: 219

Re: Intermediates

A substance doesn't have to be a product of the first elementary reaction and a reactant of the final elementary reaction. As everyone has said, the species just has to be cancelled out when adding the elementary reactants together to get the overall reaction. This could be in the first and third st...
by Kailey Brodeur 1J
Tue Mar 06, 2018 4:44 pm
Forum: General Rate Laws
Topic: Mechanisms
Replies: 1
Views: 95

Re: Mechanisms

You use the slow step elementary reaction in the reaction mechanism to write out the rate law, putting the concentration of the reactants to their stoichiometric coefficient.
by Kailey Brodeur 1J
Mon Mar 05, 2018 5:22 pm
Forum: Second Order Reactions
Topic: molecularity
Replies: 6
Views: 412

Re: molecularity

You are correct that molecularity can be determined by the reactants, but we have to remember that this concept only relates to elementary reactions and doesn't apply to overall reactions.
by Kailey Brodeur 1J
Mon Mar 05, 2018 5:18 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Elementary Reactions
Replies: 2
Views: 104

Re: Elementary Reactions

Yeah I also think it depends on the situation. Sometimes we will be given elementary steps and asked to analyze them, find the intermediates, overall reaction, and rate law. Other times, I think we could propose elementary reactions for an overall reaction, however, there would never be one correct ...
by Kailey Brodeur 1J
Mon Mar 05, 2018 5:13 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Molecularity
Replies: 3
Views: 115

Re: Molecularity

Molecularity cannot be used to describe an overall reaction because you cannot confirm which species are colliding from the overall reaction. You cannot tell which species are interacting with each other (bimolecular, termolecular) or reacting with itself (unimolecular), so molecularity is not helpf...
by Kailey Brodeur 1J
Tue Feb 27, 2018 10:17 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: 15.3 [ENDORSED]
Replies: 7
Views: 295

Re: 15.3 [ENDORSED]

The unique average rate of the reaction uses utilizes the average rate of consumption equation with the stoichiometric coefficient in the denominator. Refer to the equation at the bottom of page 613 in the textbook.
by Kailey Brodeur 1J
Tue Feb 27, 2018 10:08 pm
Forum: General Rate Laws
Topic: Elementary Reactions
Replies: 4
Views: 182

Re: Elementary Reactions

These are all accurate descriptions of elementary reactions. In order to write rate laws for these reactions, you multiply k X (the concentration of the reactant) to the power of how many times it appears on the reactant side of the equation. Refer to the chart on page 634 of the textbook as it is e...
by Kailey Brodeur 1J
Tue Feb 27, 2018 10:04 pm
Forum: General Rate Laws
Topic: Homework Problem 15.3
Replies: 4
Views: 273

Re: Homework Problem 15.3

The rate of reactions cannot be generally inferred from the the chemical equation for the reaction. So the stoichiometric coefficients are the only thing to consider.
by Kailey Brodeur 1J
Sun Feb 25, 2018 7:42 pm
Forum: Balancing Redox Reactions
Topic: Oxidation state
Replies: 5
Views: 238

Re: Oxidation state

O2 and H2 are neutral molecules; they are not ions. Only ions or ionic compounds have an oxidation number. For instance, the hydrogen ion has a +1 oxidation number and an oxygen ion has a -2 oxidation number.
by Kailey Brodeur 1J
Sun Feb 25, 2018 7:38 pm
Forum: Balancing Redox Reactions
Topic: Identifying Oxi/Red Agents [ENDORSED]
Replies: 6
Views: 348

Re: Identifying Oxi/Red Agents [ENDORSED]

Yes, you can say the entire molecule is being oxidized since the compound is giving away electors even though these electrons come from one species in the molecule.
by Kailey Brodeur 1J
Sat Feb 24, 2018 1:40 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Inert Electrodes [ENDORSED]
Replies: 3
Views: 201

Re: Inert Electrodes [ENDORSED]

Inert means it is not reactive, so an inert electrode does not actually participate in the reaction. Inert electrodes are needed to conduct electrons when there is no metal involved in the redox reaction. If a solid metal is involved, then the inert electrode is not needed. I am not sure how to choo...
by Kailey Brodeur 1J
Fri Feb 16, 2018 10:19 am
Forum: General Science Questions
Topic: Heat from Sun
Replies: 1
Views: 392

Re: Heat from Sun

I don't really know the answer to this question either. But after doing some research, the hydrogen in the sun is converted into helium through millions of reactions, producing heat as a byproduct. This heat is then given off to the atmosphere (some of which reaches the Earth) through thermal radiat...
by Kailey Brodeur 1J
Fri Feb 16, 2018 10:15 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Homework #8.55 Hess's Law
Replies: 2
Views: 117

Re: Homework #8.55 Hess's Law

I don't know if this is helpful, but the first equation you stated is the balanced chemical equation while the second one is the chemical equation utilized to find enthalpy of formation as the reactants are in amounts designed to produce exactly one mole of product.
by Kailey Brodeur 1J
Fri Feb 16, 2018 10:12 am
Forum: General Science Questions
Topic: Battery voltage
Replies: 4
Views: 377

Re: Battery voltage

I think this also has to do with the fact that we are finding the voltage of "random" chemical reactions when batteries used in everyday life are designed to utilize reactions that produce optimal voltage.
by Kailey Brodeur 1J
Wed Feb 07, 2018 9:38 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.37
Replies: 1
Views: 100

Re: 9.37

This is because parts a-c all specify 1 mol of reactant while part d just says the general reaction, and therefore doesn't have to be per mole.
by Kailey Brodeur 1J
Wed Feb 07, 2018 8:31 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: isothermal reversible expansion
Replies: 1
Views: 98

Re: isothermal reversible expansion

This is explained well in section 8.10 of the textbook, but basically, heat capacity at a constant volume is equal to change in internal energy over change in temperature. Change in internal energy is equal to (3/2)R(change in temp) for ideal gases. This formula arises from the molecular rotational ...
by Kailey Brodeur 1J
Wed Feb 07, 2018 8:22 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Determining Anode/Cathode in a Cell Diagram
Replies: 2
Views: 155

Re: Determining Anode/Cathode in a Cell Diagram

I am also confused on this, but the textbook mentions that if the overall cell potential is positive then the anode will appear on the right of the cell diagram and the cathode will appear on the left. If the cell potential is negative, meaning the overall reaction is unfavorable, the cathode and an...
by Kailey Brodeur 1J
Tue Jan 30, 2018 5:06 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.19
Replies: 3
Views: 171

Re: 9.19

Yes and also this question asks specifically for the standard entropy of vaporization which is measured in J/Kmol. It is not like the other questions that are just asking for the change in entropy for a specific amount of moles. The standard entropy of vaporization is calculated so it can later be u...
by Kailey Brodeur 1J
Tue Jan 30, 2018 4:45 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Useful Summary of Thermodynamic Definitions
Replies: 23
Views: 13689

Re: Useful Summary of Thermodynamic Definitions

These 3 situations each have a different factor that remains the same. Isobaric refers to a system in which pressure remains constant, isochloric refers to a system in which volume remains constant, and isothermal refers to a system in which temperature remains constant. This means other factors are...
by Kailey Brodeur 1J
Tue Jan 30, 2018 4:33 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.27 D
Replies: 3
Views: 130

Re: 9.27 D

Yes, that is correct. It is also easy to think about conceptually. At 1.00 atm, the gas molecules are not being "pressed" as hard, so they are not as confined as they would be at 2.00 atm. When the gas molecules are not as confined they are able to fill more volume and essentially have mor...
by Kailey Brodeur 1J
Mon Jan 22, 2018 10:23 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: delta n
Replies: 3
Views: 894

Re: delta n

If there is a limiting reactant: delta n = (moles of gas produced + excess gas reactant remaining) - moles of gas consumed
If there is no limiting reactant: delta n = moles of gas product - moles of gas reactant
by Kailey Brodeur 1J
Mon Jan 22, 2018 10:16 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Memorizing Enthalpies [ENDORSED]
Replies: 5
Views: 181

Re: Memorizing Enthalpies [ENDORSED]

You do not need to memorize any enthalpies. You just need to know common standard states, such as zinc is a solid or oxygen is a diatomic gas in order to be utilizing the correct standard enthalpies of formation
by Kailey Brodeur 1J
Mon Jan 22, 2018 10:11 am
Forum: Calculating Work of Expansion
Topic: When to use equation [ENDORSED]
Replies: 3
Views: 165

Re: When to use equation [ENDORSED]

Specifically, the textbook says that the first equation is used for an isothermal, reversible expansion of a gas. As a gas expands, the pressure decreases according to Boyle's Law which is how the equation developed. The second equation is used for non expansion work, so volume change isn't involved.
by Kailey Brodeur 1J
Mon Jan 22, 2018 10:06 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: System Types
Replies: 7
Views: 280

Re: System Types

If the system is isolated, no energy or mass can be transferred between the system and surroundings. This means that the internal energy of an isolated system cannot change (the first law of thermodynamics) delta U = q + w = 0. In a closed system, mass cannot be transferred, but energy can be. In an...
by Kailey Brodeur 1J
Wed Jan 17, 2018 9:53 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Two Work Functions
Replies: 1
Views: 79

Re: Two Work Functions

The first equation is used to determine work done against a constant external pressure. If the pressure is changing, but the work is being performed by an ideal gas, then you can use the second equation.
by Kailey Brodeur 1J
Wed Jan 17, 2018 9:48 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: R value in equation
Replies: 4
Views: 159

Re: R value in equation

You have to use the R value with the corresponding units to the other variables you are using. Just make sure the right units are canceling out.
by Kailey Brodeur 1J
Tue Jan 16, 2018 3:41 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: standard state of substances
Replies: 4
Views: 184

Re: standard state of substances

We also should know what physical state some of the common elements are in. For instance, we should know that lead, gold, and iron are solids at room temp. These standard states will be used in standard enthalpy of formation and can be used with Hess's Law to determine the standard enthalpy of essen...
by Kailey Brodeur 1J
Tue Jan 16, 2018 2:59 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: What does R stand for?
Replies: 13
Views: 789

Re: What does R stand for?

R is the ideal gas constant. You decide what value of R you should used based upon what units you are using.
by Kailey Brodeur 1J
Thu Jan 11, 2018 3:18 pm
Forum: Phase Changes & Related Calculations
Topic: Ideal Gas
Replies: 5
Views: 234

Re: Ideal Gas

An ideal gas is a hypothetical gas who obeys all the gas laws exactly because it is seen to occupy negligible space and has no interactions with other molecules. I think that this is important for question 31 because it allows you to apply all gas laws and their corresponding equations.
by Kailey Brodeur 1J
Thu Jan 11, 2018 3:13 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law example from lecture
Replies: 3
Views: 164

Re: Hess's Law example from lecture

Yes these reactions are added together in order to get the final reaction that we are looking at. The enthalpies can also be added together since enthalpy is a state property. It doesn't matter what pathway is taken to get to the specific enthalpy, all that matters is the current value. That is why ...
by Kailey Brodeur 1J
Thu Jan 11, 2018 1:48 pm
Forum: Phase Changes & Related Calculations
Topic: Enthalpy of Intramolecular Forces
Replies: 3
Views: 377

Re: Enthalpy of Intramolecular Forces

I don't think that the intramolecular forces are affected because these are the forces that hold the actual molecules together. The molecules themselves are not changing when a phase change occurs, just the way the molecules are arranged. By altering the intramolecular forces, a chemical change woul...

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