## Search found 33 matches

- Sun Mar 11, 2018 3:44 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Activation Energy
- Replies:
**4** - Views:
**262**

### 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?

- Sun Mar 11, 2018 3:36 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Collision Cross Section
- Replies:
**2** - Views:
**317**

### 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?

- Sun Mar 11, 2018 2:11 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Reaction Too Slow to Include in Mechanism
- Replies:
**1** - Views:
**154**

### 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...

- Tue Mar 06, 2018 11:42 am
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: K'
- Replies:
**7** - Views:
**474**

### 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.

- Tue Mar 06, 2018 10:42 am
- Forum: General Rate Laws
- Topic: When to Use Avg. vs Instantaneous
- Replies:
**5** - Views:
**250**

### 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.

- Tue Mar 06, 2018 10:37 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Pre Equilibrium Condition
- Replies:
**1** - Views:
**110**

### 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...

- Tue Mar 06, 2018 10:25 am
- Forum: First Order Reactions
- Topic: Psuedo First Order Reaction
- Replies:
**2** - Views:
**186**

### 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?

- Tue Mar 06, 2018 10:18 am
- Forum: Zero Order Reactions
- Topic: Slope From
- Replies:
**5** - Views:
**417**

### Slope From

Can someone please explain why it is important for us to know the slope-intercept form for some of the equations?

- 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:
**429**

### 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...

- Mon Feb 26, 2018 9:19 pm
- Forum: First Order Reactions
- Topic: Calculating slope
- Replies:
**4** - Views:
**345**

### 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.

- Mon Feb 26, 2018 9:09 pm
- Forum: First Order Reactions
- Topic: Ways of determining what order reactions are
- Replies:
**2** - Views:
**177**

### 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?

- 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:
**310**

### 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?

- Fri Feb 23, 2018 11:25 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Reaction Favoring Products
- Replies:
**2** - Views:
**195**

### 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?

- 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:
**146**

### 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?

- 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:
**177**

### 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.

- Tue Feb 13, 2018 11:27 am
- Forum: Calculating Work of Expansion
- Topic: equilbrium = reversible
- Replies:
**3** - Views:
**251**

### 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.

- Tue Feb 13, 2018 11:24 am
- Forum: Calculating Work of Expansion
- Topic: Constant Pressure and Volume
- Replies:
**1** - Views:
**163**

### 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?"

- Tue Feb 06, 2018 9:09 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: entropy chnage
- Replies:
**1** - Views:
**141**

### 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!

200J + -50J = 150J! Hope it helps!

- Tue Feb 06, 2018 9:01 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: exothermic
- Replies:
**5** - Views:
**354**

### 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.

- Tue Feb 06, 2018 8:59 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Kelvin
- Replies:
**4** - Views:
**305**

### 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!

- Tue Jan 30, 2018 1:36 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Isobaric RXN
- Replies:
**1** - Views:
**210**

### 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...

- Tue Jan 30, 2018 1:30 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: isothermal
- Replies:
**5** - Views:
**309**

### 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.

- Tue Jan 30, 2018 1:28 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: 9.11
- Replies:
**2** - Views:
**180**

### Re: 9.11

Since you are working with ideal gases you would use the R value of 8.314 J/K mol.

- Tue Jan 30, 2018 1:26 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: unit of entropy
- Replies:
**11** - Views:
**620**

### 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!

- Wed Jan 24, 2018 7:44 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Heat capacity
- Replies:
**2** - Views:
**241**

### 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...

- Wed Jan 24, 2018 7:33 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Calorimetry
- Replies:
**4** - Views:
**275**

### Re: Calorimetry

I would recommend staying in degrees Celsius because it will easily cancel out when proportionally setting up the math.

- 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:
**448**

### 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. :)

- Fri Jan 19, 2018 10:36 am
- Forum: Phase Changes & Related Calculations
- Topic: Phase Change and Energy Absorbed
- Replies:
**1** - Views:
**114**

### 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!

- 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:
**4685**

### 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.

- Fri Jan 19, 2018 10:20 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Delta U？
- Replies:
**7** - Views:
**2390**

### 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.

- Fri Jan 12, 2018 4:15 pm
- Forum: Phase Changes & Related Calculations
- Topic: Irreversible process vs reversible process
- Replies:
**4** - Views:
**200**

### 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...

- Fri Jan 12, 2018 4:04 pm
- Forum: Phase Changes & Related Calculations
- Topic: Boiling water vs. steam
- Replies:
**6** - Views:
**713**

### 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...

- Fri Jan 12, 2018 3:57 pm
- Forum: Phase Changes & Related Calculations
- Topic: Intensive vs. Extensive
- Replies:
**5** - Views:
**644**

### 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...