Search found 33 matches

by Sarah Sharma 2J
Sun Mar 11, 2018 3:44 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Activation Energy
Replies: 4
Views: 142

Activation Energy

When activation energy is at its optimum, what does that mean for collisions? Are they taking place at the fastest at this point?
by Sarah Sharma 2J
Sun Mar 11, 2018 3:36 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Collision Cross Section
Replies: 2
Views: 99

Collision Cross Section

Can someone please explain the importance of knowing the collision cross section? Why do we need to know the area at which a molecule presents itself as a target. Also, how do we know if a molecule IS a target? When a collision happens aren't they both considered targets?
by Sarah Sharma 2J
Sun Mar 11, 2018 2:11 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction Too Slow to Include in Mechanism
Replies: 1
Views: 63

Reaction Too Slow to Include in Mechanism

In the textbook, in section 15.8, when describing rate laws and mechanisms the textbook says that "The reverse of step 2 is too slow to affect the rate and so is not included." This is when referring to the example of N2O2. How can we tell that this reaction is too slow to include in the m...
by Sarah Sharma 2J
Tue Mar 06, 2018 11:42 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: K'
Replies: 7
Views: 207

Re: K'

K' is simply the substitution during a pseudo reaction that sets one of the reactants at a high concentration so that we can only focus on the changing aspect of one reactant. It makes it simpler to analyze the changing rate of the reaction when only focusing on one reactant.
by Sarah Sharma 2J
Tue Mar 06, 2018 10:42 am
Forum: General Rate Laws
Topic: When to Use Avg. vs Instantaneous
Replies: 5
Views: 104

Re: When to Use Avg. vs Instantaneous

Yes, instantaneous rate should always be used because we wish to know the rate of the reaction at any given moment .Instantaneous rate allows for us to solve that even with the changing slope as the rate that the reaction goes to products may not always be consistent, the rate can change.
by Sarah Sharma 2J
Tue Mar 06, 2018 10:37 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pre Equilibrium Condition
Replies: 1
Views: 50

Pre Equilibrium Condition

Can someone please explain the purpose of knowing the pre equilibrium condition? If we are solving in regards to equilibrium why is it useful to know the condition right before? Is it because it gives tells us the point where right before the reaction contains its highest energy and is at its most u...
by Sarah Sharma 2J
Tue Mar 06, 2018 10:25 am
Forum: First Order Reactions
Topic: Psuedo First Order Reaction
Replies: 2
Views: 94

Psuedo First Order Reaction

Hello! Can someone please explain the purpose of the Pseudo first order reaction? I understand that it changes the way the equation is visualized so that we can only focus on one reactant however, how would one go about solving the substitution?
by Sarah Sharma 2J
Tue Mar 06, 2018 10:18 am
Forum: Zero Order Reactions
Topic: Slope From
Replies: 5
Views: 217

Slope From

Can someone please explain why it is important for us to know the slope-intercept form for some of the equations?
by Sarah Sharma 2J
Mon Feb 26, 2018 9:23 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Q and K
Replies: 7
Views: 188

Re: Q and K

The concepts of Q and K are the same the variable changes depending on the context of the question. Q is used when referring to two concentrations that are not at equilibrium and can be utilizded at any point of the reaction. Whereas K is used when referring to concentrations at equilibrium. Q can b...
by Sarah Sharma 2J
Mon Feb 26, 2018 9:19 pm
Forum: First Order Reactions
Topic: Calculating slope
Replies: 4
Views: 130

Re: Calculating slope

The slope is negative because it will indicate which direction the gradient/slope will. You will see that when deriving the equation for the second order reaction, the negatives can cancel, making the gradient positive.
by Sarah Sharma 2J
Mon Feb 26, 2018 9:09 pm
Forum: First Order Reactions
Topic: Ways of determining what order reactions are
Replies: 2
Views: 84

Ways of determining what order reactions are

Hello, I was wondering what are some ways of classifying what orders certain reactions are in? What are some key details that we can look for?
by Sarah Sharma 2J
Fri Feb 23, 2018 11:28 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Standard State with Nernst Equation
Replies: 4
Views: 147

Standard State with Nernst Equation

When given a reaction and we are asked to calculate using the Nernst equation, when can we assume that it is in standard state if it doesn't specify?
by Sarah Sharma 2J
Fri Feb 23, 2018 11:25 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Reaction Favoring Products
Replies: 2
Views: 88

Reaction Favoring Products

Can someone please explain to me why when the cathode has a higher E value than the anode, the reaction favors the products?
by Sarah Sharma 2J
Fri Feb 23, 2018 11:19 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Reduced State to Standard State
Replies: 1
Views: 72

Reduced State to Standard State

If a question asked to go from a standard reduced potential to a standard potential, how would I do that?
by Sarah Sharma 2J
Tue Feb 13, 2018 11:53 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Change in temp vs Change in volume equations
Replies: 2
Views: 90

Re: Change in temp vs Change in volume equations

To add to the comment above, the C can imply either constant volume or pressure, due to the temperature change, either can be held constant. Constant pressure denoted (Cp) would be 5/2 R and Constant Volume would be denoted as (Cv) 3/2R.
by Sarah Sharma 2J
Tue Feb 13, 2018 11:27 am
Forum: Calculating Work of Expansion
Topic: equilbrium = reversible
Replies: 3
Views: 135

Re: equilbrium = reversible

Due to the fact that equilibrium is annotated with the arrows pointing both ways, it is considered reversible. Also, dynamic equilibrium is defined as the rate of the forward reaction being equal to the rate of the reverse reaction, therefore equilibrium is always considered a reversible reaction.
by Sarah Sharma 2J
Tue Feb 13, 2018 11:24 am
Forum: Calculating Work of Expansion
Topic: Constant Pressure and Volume
Replies: 1
Views: 109

Constant Pressure and Volume

When calculating for entropy, when will we know when to implement 5/3 R and 3/2 R for an expression? Are there any hints in the equation other than "at constant pressure/volume?"
by Sarah Sharma 2J
Tue Feb 06, 2018 9:09 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: entropy chnage
Replies: 1
Views: 57

Re: entropy chnage

Its negative because the reservoir that was at 800K in the transfer of heat is the reservoir that is losing heat, therefore it is negated in the process. The end results should come out to about
200J + -50J = 150J! Hope it helps!
by Sarah Sharma 2J
Tue Feb 06, 2018 9:01 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: exothermic
Replies: 5
Views: 166

Re: exothermic

If it turns cold, it means that the reaction in the flask absorbed heat from its surroundings and would therefore be endothermic! When a reaction is exothermic the flask should feel warm due to the release of heat/energy.
by Sarah Sharma 2J
Tue Feb 06, 2018 8:59 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Kelvin
Replies: 4
Views: 142

Re: Kelvin

Yes, always convert to Kelvin when calculating for entropy. Also, when looking at the units for some of the constants, it will tell you whether to use Celsius or Kelvin! Usually Kelvin though!
by Sarah Sharma 2J
Tue Jan 30, 2018 1:36 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isobaric RXN
Replies: 1
Views: 120

Re: Isobaric RXN

When P is constant, if dealing with an ideal gas the way to solve for entropy is Delta S= nCpln (V2/V1) Cp refers to the constant pressure which can be found by multiplying the ideal gas constant (R or 8.314J/K mol) by 5/2. So the equation when calculating for a reversible reaction will look like De...
by Sarah Sharma 2J
Tue Jan 30, 2018 1:30 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: isothermal
Replies: 5
Views: 142

Re: isothermal

To agree with the statement above, isothermal is no exchange of heat or energy. Therefore, the temperature stays constant and Delta T should equal zero.
by Sarah Sharma 2J
Tue Jan 30, 2018 1:28 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.11
Replies: 2
Views: 98

Re: 9.11

Since you are working with ideal gases you would use the R value of 8.314 J/K mol.
by Sarah Sharma 2J
Tue Jan 30, 2018 1:26 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: unit of entropy
Replies: 11
Views: 277

Re: unit of entropy

When completing the math, usually the way the problem is set up will allow for the units to cancel out to being J/K (joules per kelvin), this can be used as another way of testing if the problem is correct!
by Sarah Sharma 2J
Wed Jan 24, 2018 7:44 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat capacity
Replies: 2
Views: 118

Re: Heat capacity

Heat capacity tells the amount of heat that is needed in order to raise the temperature of a substance by 1 degree celsius. This relates to specific heat capacity as this is the amount of energy needed to raise the temperature of one gram of a substance by 1 degree celsius. A large heat capacity, mu...
by Sarah Sharma 2J
Wed Jan 24, 2018 7:33 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimetry
Replies: 4
Views: 138

Re: Calorimetry

I would recommend staying in degrees Celsius because it will easily cancel out when proportionally setting up the math.
by Sarah Sharma 2J
Wed Jan 24, 2018 7:31 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heat capacity question
Replies: 5
Views: 242

Re: Heat capacity question

The following equations are used when the problem gives an ideal gas with either constant pressure (Cp) or constant volume (Cv). We multiply these numbers by the ideal gas constant in order to obtain the heat capacity if an ideal gas at either constant volume or pressure. :)
by Sarah Sharma 2J
Fri Jan 19, 2018 10:36 am
Forum: Phase Changes & Related Calculations
Topic: Phase Change and Energy Absorbed
Replies: 1
Views: 71

Phase Change and Energy Absorbed

Can someone please explain to me why when calculating for a phase change and finding the energy released/absorbed we add MC(Delta)T to M(Delta)H and set them both equal to q? Thank you!
by Sarah Sharma 2J
Fri Jan 19, 2018 10:26 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Why is using bond enthalpies the least accurate method of finding reaction enthalpies?
Replies: 5
Views: 460

Re: Why is using bond enthalpies the least accurate method of finding reaction enthalpies?

Bond enthalpies are composed of multiple averages and therefore are an overall average. Whereas other values nad methods such as enthalpy of formation are much more accurate.
by Sarah Sharma 2J
Fri Jan 19, 2018 10:20 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta U?
Replies: 7
Views: 238

Re: Delta U?

Delta U is referred to as the change in internal energy of a system. Delta U is actually equal to q + w whereas q is the heat input or Delta H. w= -P(Vfinal-Vinitial). If in a problem the system has a constant volume and no expansionary work is performed then w=0.
by Sarah Sharma 2J
Fri Jan 12, 2018 4:15 pm
Forum: Phase Changes & Related Calculations
Topic: Irreversible process vs reversible process
Replies: 4
Views: 141

Re: Irreversible process vs reversible process

An irreversible reaction is a reaction where one can not take the products and revert them back to the reactants; these reactants are usually represented with an arrow pointing towards the products because there is no going back. Whereas a reversible reaction one can go from the reactants to the pro...
by Sarah Sharma 2J
Fri Jan 12, 2018 4:04 pm
Forum: Phase Changes & Related Calculations
Topic: Boiling water vs. steam
Replies: 6
Views: 255

Re: Boiling water vs. steam

As said above, when looking at the phase change graph it is evident that it requires a larger input of heat to turn water into vapor than it does to turn solid ice into liquid. This is because the horizontal line that represents a phase change from liquid to vapor is also much lengthier than that of...
by Sarah Sharma 2J
Fri Jan 12, 2018 3:57 pm
Forum: Phase Changes & Related Calculations
Topic: Intensive vs. Extensive
Replies: 5
Views: 271

Re: Intensive vs. Extensive

The most basic definition and difference between an intensive and extensive property is that an intensive property is a physical property of a system that is completely independent of size. Whereas an extensive property is a bit more specific in that is is dependent on the amount of matter present i...

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