When you calculate the enthalpy of state change, do you generally do this:

Enthalpy of fus/sub of given substance x mass of substance

Is that the correct way to do it?

## Search found 38 matches

- Sat Mar 18, 2017 9:34 am
- Forum: Phase Changes & Related Calculations
- Topic: General formula for phase changes for enthalpy.
- Replies:
**2** - Views:
**448**

- Mon Mar 13, 2017 9:58 pm
- Forum: Student Social/Study Group
- Topic: Saturday Review Session
- Replies:
**1** - Views:
**404**

### Saturday Review Session

Hey everyone,

Is anybody interested in forming a Finals Review session this Saturday? I feel that it will be very helpful to review for what is to come? What do you say?

Study location and time is yet to be determined. Currently, I'm thinking of Hedrick Hall's lounge. I'm open to other ideas.

Is anybody interested in forming a Finals Review session this Saturday? I feel that it will be very helpful to review for what is to come? What do you say?

Study location and time is yet to be determined. Currently, I'm thinking of Hedrick Hall's lounge. I'm open to other ideas.

- Wed Mar 08, 2017 6:52 pm
- Forum: *Alkanes
- Topic: Iso, Neo, and Tert
- Replies:
**3** - Views:
**427**

### Iso, Neo, and Tert

Can anybody explain to me what Iso, Neo, and Tert are in common names?

So Iso involves the connection of Carbon bonds? And also Neo and Tert. But what exactly makes them different to one another?

So Iso involves the connection of Carbon bonds? And also Neo and Tert. But what exactly makes them different to one another?

- Sat Mar 04, 2017 11:41 pm
- Forum: *Alkanes
- Topic: What exactly is carbanion & ambident nucelophiles? [ENDORSED]
- Replies:
**1** - Views:
**290**

### What exactly is carbanion & ambident nucelophiles? [ENDORSED]

I keep looking at the two terms in the book, but I keep getting confused upon the wording?

Can somebody explain this to me in a way that even a normal person outside of chemistry can understand this please?

Thanks in advance.

Can somebody explain this to me in a way that even a normal person outside of chemistry can understand this please?

Thanks in advance.

- Sat Feb 18, 2017 10:27 am
- Forum: First Order Reactions
- Topic: Homework Help 15.25 [ENDORSED]
- Replies:
**1** - Views:
**400**

### Homework Help 15.25 [ENDORSED]

Here's the question: Dinitrogen pentoxide, N2O5, decompose by first-order kinetics with rate constant of 3.7 x 10^-5 s^-1 at 298 K. I've dealt with A and B already. C is confusing me the most. The question is asking me "How much time (in minutes) will elapse before the N205 concentration decrea...

- Thu Feb 16, 2017 3:51 pm
- Forum: General Rate Laws
- Topic: Homework Help 15.1
- Replies:
**4** - Views:
**506**

### Homework Help 15.1

I'm a bit confused with this question. So the question states: Complete the following statements relating to the production of ammonia by the Haber process, for which the overall reaction is N2 + 3H2 -> 2 NH3 a) the rate of consuption of N2 is _____ times the rate of consumption of H2. When I first ...

- Wed Feb 15, 2017 10:16 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: When do you add Pt?
- Replies:
**3** - Views:
**366**

### When do you add Pt?

I'm getting confused with the whole Pt thing.

Pt needs to be added when the materials in cell aren't solid. But I've seen a few Pt added to cell where it has solid states. Is there a general rule here when adding Pt to cell reactions?

Pt needs to be added when the materials in cell aren't solid. But I've seen a few Pt added to cell where it has solid states. Is there a general rule here when adding Pt to cell reactions?

- Sun Feb 12, 2017 12:56 am
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: What is Q again?
- Replies:
**1** - Views:
**266**

### What is Q again?

So I understand Q is part of the Nernst equation.

What I'm confused about is what makes up Q again? When I look at the cell equation, do I just choose the ions or what?

What I'm confused about is what makes up Q again? When I look at the cell equation, do I just choose the ions or what?

- Sun Feb 05, 2017 6:42 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: How do you deal with 3 given elements for a half reaction?
- Replies:
**1** - Views:
**224**

### How do you deal with 3 given elements for a half reaction?

I'm honestly used to and fine with 4 elements being used, such as: Reactant + Reactant -> Product + Product However, there are times when I have a tough time with three. For example, Reactant + Reactant -> Product or Reactant -> Product + Product These given amount of elements confuse me, seeing how...

- Sun Feb 05, 2017 2:26 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Homework Help 14.9 (Balancing Equation)
- Replies:
**1** - Views:
**279**

### Homework Help 14.9 (Balancing Equation)

Hey, do you know how to balance the equation

2 Ce^4 + 3 I ^- -> 2 Ce^3+ + I3^-?

I'm trying to figure out how electrons are transferred in this.

2 Ce^4 + 3 I ^- -> 2 Ce^3+ + I3^-?

I'm trying to figure out how electrons are transferred in this.

- Sat Feb 04, 2017 9:52 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Homework Help 14.9
- Replies:
**3** - Views:
**270**

### Re: Homework Help 14.9

So I've worked on the problem, I'm not sure if I'm doing this correctly:

2 Ce^4 -> 2 Ce^3+ (this means that one electron is transferred?)

3 I ^- -> I 3 ^- (I'm not really sure about this one though).

2 Ce^4 -> 2 Ce^3+ (this means that one electron is transferred?)

3 I ^- -> I 3 ^- (I'm not really sure about this one though).

- Sat Feb 04, 2017 6:45 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Homework Help 14.9
- Replies:
**3** - Views:
**270**

### Homework Help 14.9

So the question is: Calculate the standard reaction Gibbs free energy for the following reactions: a) 2 Ce^4+(aq) + 3 I^-(aq) -> 2 Ce^3+(aq) + I 3 ^- (aq) So I understand that the formula is Delta Gr = -nFE, where F and E are given to me. But how exactly do I figure out n? N is moles, but where exac...

- Fri Feb 03, 2017 6:52 pm
- Forum: Balancing Redox Reactions
- Topic: How do I find oxidation number?
- Replies:
**2** - Views:
**339**

### How do I find oxidation number?

This seems like I'm asking this question WAY too late in this, but how do I find the oxidation number of an element in a chemical equation? For example: MnO4^- + H2C2O4 -> Mn^2+ + CO2 When focusing on MnO4^- -> Mn^2+, how come Mn in MnO4 has (-7) and O4 has -2, and Mn^2+ has +2? I'm lost here.

- Sun Jan 29, 2017 3:58 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: 9.45 Help.
- Replies:
**1** - Views:
**245**

### 9.45 Help.

So the question is asking me this:

Calculate the changes in entropy of the surroundings and of the system for (a) the vaporization of 1.00 mol CH4 at is normal boiling point.

So I know the formula is Delta S = - Delta H / T. Why is T = 111.7 K?

Calculate the changes in entropy of the surroundings and of the system for (a) the vaporization of 1.00 mol CH4 at is normal boiling point.

So I know the formula is Delta S = - Delta H / T. Why is T = 111.7 K?

- Fri Jan 27, 2017 6:16 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Q and -Q
- Replies:
**2** - Views:
**283**

### Q and -Q

Hey, I just want to confirm something.

Whenever I see this: q=-q, does -q mean that there is heat gain or loss? I get kind of confused with this.

Whenever I see this: q=-q, does -q mean that there is heat gain or loss? I get kind of confused with this.

- Sun Jan 22, 2017 2:17 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Enthalpy Formula
- Replies:
**2** - Views:
**281**

### Enthalpy Formula

Can anyone explain to me the formula for enthalpy?

I keep on getting mixed up with a lot of formulas.

I keep on getting mixed up with a lot of formulas.

- Mon Jan 16, 2017 12:11 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: What is R?
- Replies:
**1** - Views:
**211**

### What is R?

So I'm looking at the formula

C P,M = C V,m + R. I understand C P,M and C V,m. But what exactly is R?

C P,M = C V,m + R. I understand C P,M and C V,m. But what exactly is R?

- Fri Jan 13, 2017 5:47 pm
- Forum: Phase Changes & Related Calculations
- Topic: 8.21 Help
- Replies:
**2** - Views:
**306**

### 8.21 Help

So I'm looking at the question and the solution manual, but I'm still kind of lost.

Which section talks about this sort of concept (e.g. 8.1, 8.2, 8.3)?

Which section talks about this sort of concept (e.g. 8.1, 8.2, 8.3)?

- Fri Jan 13, 2017 2:21 pm
- Forum: Phase Changes & Related Calculations
- Topic: Homework Help 8.9
- Replies:
**4** - Views:
**440**

### Homework Help 8.9

So I've been doing the calculations, and reached the point where I'm supposed to concert -1.48 L atm to J.

But where does 8.314 J and 0.08206 even come from?

But where does 8.314 J and 0.08206 even come from?

- Thu Dec 01, 2016 11:35 pm
- Forum: *Titrations & Titration Calculations
- Topic: Homework Help 13.27
- Replies:
**1** - Views:
**237**

### Homework Help 13.27

So...I'm working on the problem, and I've reached part D.

It's asking me to find pH at the stochiometric point. How exactly do I do that? I'm looking at the student solution manual, and it merely told me to convert my NaOH mol to L. But how do I find the pH with just L?

It's asking me to find pH at the stochiometric point. How exactly do I do that? I'm looking at the student solution manual, and it merely told me to convert my NaOH mol to L. But how do I find the pH with just L?

- Thu Dec 01, 2016 1:03 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Homework Help 12.69
- Replies:
**1** - Views:
**292**

### Homework Help 12.69

So I've been working on question 12.69, and it's asking me to find the PH For part A, it's asking me to find the PH of 0.19 M NH4Cl(aq). So the first step is to create the formula for this. However, the student solution manual is telling me this: NH4+ + H20 -> H30 + NH3 Whatever happened to the Cl p...

- Mon Nov 28, 2016 8:38 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Homework Help 12.75 [ENDORSED]
- Replies:
**1** - Views:
**344**

### Homework Help 12.75 [ENDORSED]

I need help on 12.75. So the question is asking... During the analysis of an uknown acid HA, a 0.010 M solution of the sodium salt of the acid was found to have a pH of 10.35. Use Table 12.1 to write the formula of the acid. I'm looking at the student solution, but...I'm still lost. Can anybody expl...

- Mon Nov 28, 2016 8:36 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Homework Help 12.65
- Replies:
**4** - Views:
**733**

### Homework Help 12.65

So I need help on this question. Determine whether an aqueous soluiton of each of the following salts has a pH equal to, greater than, or less than 7. If pH > 7 or pH < 7, wrtie a chemical euqation to justfy your answer. a) Nh4Br etc. I'm confused. All I'm seeing are given formulas. What are you sup...

- Mon Nov 28, 2016 8:31 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Homework Help 12.33
- Replies:
**1** - Views:
**320**

### Homework Help 12.33

So the question is asking "A student added solid Na2O to a 200.0-mL volumetric flask, which was then filled with water, resulting in 200.0 mL of NaOh solution. 5.00 mL of the solution was then transferred to another voluemtric flask and diluted to 500.0 mL. The pH of the diluted solution is 13....

- Sat Nov 26, 2016 1:08 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Homework Help 12.21
- Replies:
**2** - Views:
**432**

### Homework Help 12.21

So the question is asking me "What is the molarity of OH- in solutions with the following concentrations of H30+: ..." I've looked up the solution on part a), but I'm very confused about something. Where did the value of 1.0 x 10^-14 come from? I tried looking all over the text book, but i...

- Wed Nov 23, 2016 3:35 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Homework Help 11.39
- Replies:
**1** - Views:
**355**

### Homework Help 11.39

Hello.

So I'm looking at question 11.39, and they showed me the calculations. But I don't exactly understand what is going on in this question. An explanation is appreciated.

From,

Andrew

So I'm looking at question 11.39, and they showed me the calculations. But I don't exactly understand what is going on in this question. An explanation is appreciated.

From,

Andrew

- Wed Nov 23, 2016 2:53 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 11.37 Homework Help
- Replies:
**1** - Views:
**319**

### 11.37 Homework Help

So the question is asking: For the reaction N2(g) + 3H2(g) -> 2 NH3(g) at 400. K, K = 41. Find the value of K for each of the following reactions at the same temperature. a) 2 NH3 -> N2 + 3H2 After some calculations and looking at the solution manual, how come (N2)(H2)^3/NH^3 = 1/41, specifically N2...

- Thu Nov 17, 2016 10:36 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: General trend in pressures?
- Replies:
**1** - Views:
**1900**

### General trend in pressures?

So what are the general trends in changing the parital pressures of the equations with equiblibrium? If you increase the pressure of a product, the reaction will shift towards the reactants. If you decrease the pressure of the product, the reaction will what ? If you decrease the pressure of a react...

- Sun Nov 13, 2016 7:40 am
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies:
**7834** - Views:
**1088782**

### Re: Post All Chemistry Jokes Here

Unfortunately, I was late to post something for last week. But hopefully, to make up for it, I hope this joke can make up for it.

- Sun Nov 13, 2016 7:36 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: The difference between K, Kc, and Kp
- Replies:
**2** - Views:
**401**

### The difference between K, Kc, and Kp

Hello.

I'm just getting confused with K, Kc, and Kp for chemical equilibrium. What exactly is the difference between them.

From,

Andrew.

I'm just getting confused with K, Kc, and Kp for chemical equilibrium. What exactly is the difference between them.

From,

Andrew.

- Mon Oct 31, 2016 1:26 am
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Electron Configurations for D-Groups
- Replies:
**1** - Views:
**281**

### Electron Configurations for D-Groups

So I'm looking at this question:

Give the ground state electron configuration for the following:

Cr^+

I thought it was 3d^3 4s^2.

However, the answer, given by the course reader, is 3d^5. Why is that?

Give the ground state electron configuration for the following:

Cr^+

I thought it was 3d^3 4s^2.

However, the answer, given by the course reader, is 3d^5. Why is that?

- Sun Oct 30, 2016 10:11 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Determining Bond Angles For Bent/Angular shapes
- Replies:
**1** - Views:
**309**

### Determining Bond Angles For Bent/Angular shapes

Hey guys. So I've been looking at bent/angular molecule shapes for a while now, but I'm having trouble finding the given angle. Most of the time, when I look at the textbook, I'm give a variety of angles. So does that mean that when I'm given a question to find the bond angle of a bent/angular molec...

- Sat Oct 29, 2016 1:20 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Memorization Tips
- Replies:
**3** - Views:
**516**

### Memorization Tips

Hello there.

Is there anybody out there that knows any tips or tricks to memorize the VESPER models? Because they all seem rather tricky to memorize.

Thanks.

Andrew U.

Is there anybody out there that knows any tips or tricks to memorize the VESPER models? Because they all seem rather tricky to memorize.

Thanks.

Andrew U.

- Mon Oct 24, 2016 10:59 am
- Forum: Lewis Structures
- Topic: Quiz 2 Prep. Question 6 [ENDORSED]
- Replies:
**7** - Views:
**1009**

### Quiz 2 Prep. Question 6 [ENDORSED]

So the question is asking me the resonance for (NH2)COCH3

I've managed to find one structure for it. But I can't seem to find the other, unless I change the formal charge of the compound. Is that what I'm supposed to do?

I've managed to find one structure for it. But I can't seem to find the other, unless I change the formal charge of the compound. Is that what I'm supposed to do?

- Mon Oct 17, 2016 10:11 am
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: 2.1
- Replies:
**4** - Views:
**1285**

### 2.1

So the question asked me about an electron in a hydrogen atom undergoes a transition from the 1s orbital to a 2p orbital. Then it asked me which of the following increases. Every part (a,b,c,d) increases. What I'm asking here is that in general, when an orbital "levels up" (1s to 2p for ex...

- Sat Oct 15, 2016 8:28 am
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: S, P, D, and F Orbitals [ENDORSED]
- Replies:
**4** - Views:
**628**

### S, P, D, and F Orbitals [ENDORSED]

I'm a bit confused with the whole S, P, D, and F orbitlals.

But they're basically spaces, correct? And each space has a certain number of electrons. I don't know the rest of the details, but can anybody explain it to me in simple detail so I can build it up from there? Thanks.

From,

Andrew

But they're basically spaces, correct? And each space has a certain number of electrons. I don't know the rest of the details, but can anybody explain it to me in simple detail so I can build it up from there? Thanks.

From,

Andrew

- Sat Oct 08, 2016 2:02 pm
- Forum: Photoelectric Effect
- Topic: The equation (pg. 13 of textbook) [ENDORSED]
- Replies:
**1** - Views:
**285**

### The equation (pg. 13 of textbook) [ENDORSED]

Hello there, I seem to be having a problem understanding this formula.

So the formula is 1/2mv^2 = hv - Φ. I keep reading it, but I can't understand what its purpose or the variables are. I would highly appreciate it if somebody manages to explain it in simple terms.

From,

Andrew

So the formula is 1/2mv^2 = hv - Φ. I keep reading it, but I can't understand what its purpose or the variables are. I would highly appreciate it if somebody manages to explain it in simple terms.

From,

Andrew

- Mon Sep 26, 2016 3:15 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Fundamental E, E.23, Part D
- Replies:
**1** - Views:
**366**

### Fundamental E, E.23, Part D

So the question here is (I've solved A, B, C): Calculate the amount (in moles) of (d) H2O in 2.00 g Na2CO3 x 10 H20. So for the first step, I did this: (2.00 g Na2CO3 x 10 H20) x (1 mol Na2CO3 x 10 H20 / (???)). The ??? part means I'm confused. When I calculated the molar mass for Na2CO3 x 10 H20, i...