Chemical Equilibrium

Hey everyone! I guess I have to scribe for today because no one's been doing it lately! 

okay lets start.. 

Lately we have been learning about Chemical Equilibrium. 

What we did last class was learn about "Le Chatelier's Principle" 

This principle states that "When the system at equilibrium is subjected to stress, the system will adjust so as to relieve the stress." 

Changing of Concentration

In a system, a change in the concentration of products or reactants present at the equilibrium, combine to form a stress. At equilibrium, the ratio of products to reactant concentrations is constant. 

When adding more reactant or removing of the products, it would upset the equilibrium. 

To relieve the stress, you need to form more of the products or use up the reactant. 

note: 

a) Increasing the concentration of a reactant shifts an equilibrium to the products (or right hand) side because the rate of the forwards reaction is increased. 

b) Increasing the concentration of a product shifts an equilibrium to the reactant (or left hand) side because the rate of the reverse reaction is speeds up. 

c) Decreasing the concentration of a reactant (by removal or by compounding it with something else of by precipitation) shifts an equilibrium to the reactants (left hand) side because the forwards reaction is slowed down. The reverse reaction will 'overtake' the forwards reaction. 

d) Decreasing the concentration of a product shifts an equilibrium to the products (right hand) side because the reverse reaction is slowed and the forward reaction 'overtakes'. 

 

Pressure Changes 

N2O4(g) <-----       ----->2NO2(g)

                                                      Very light yellow, almost colorlesss              Brown 

Increases pressure will cause more collisions to take place between gaseous molecules (pressure is a measure of the number of particles per unit volume). 

• An increase in pressure will favour the reaction involving the most particles. 
• An increase in pressure favours 2NO2 molecules reacting more than one N2O4 reacting. 
• The reverse reaction speeds up. 
• The equilibrium shifts to the left hand side.    Ex. A lighter color is produced, after an expected initial darkening caused by the original color being 'compressed'. 

If the pressure is decreased, the initial color thins but rapidly darkens. The equilibrium has shifted to the right hand side because the reverse reaction has slowed down. The collisions have been reduced in frequency. 

Pressure changes only matter if there is a different number of gas molecules on each side. Pressure changes are irrelevant if there are no gas molecules in the reaction. 

Ex. 

H2(g) + I2(g) <----     ----> 2HI(g)

There is no change in Equilibrium position. 

Temperature Change 

An increase in temperature speeds up an reaction. An endothermic reaction is helped more by a temperature rise than an exothermic reaction. 

Endothermic

N2O4(g) <---------                 ---------> 2NO2(g)

                                                      Dinitrogen tetaoxide              Exothermic            Nitrogen Dioxide 

                                               ( very light yellow, colorless )                                                   ( brown ) 

• Increasing temperature will favour the forwards reaction more so that the reverse, and so the color darkens and the equilibrium shifts to the right hand side. 
• Decreasing temperature slows the endothermic reaction the most, and so the forward reaction slows drastically and the reverse reaction wins, which means that the color lightens as the equilibrium shifts to the left side. 

Effect of a Catalyst 

A catalyst makes an easier path for the reaction, the path for the reverse reaction is made equally easier. A catalyst will not shift an equilibrium position because both rates are equally increased. The equilibrium is achieved quicker in time and under easier conditions.

However, 

If a catalyst is added to a system which is not at equilibrium, the system will reach equilibrium much quicker since forward and reverse reaction rated are increased. 

Well, I think that's basically what we learned on Monday. 

Remember to do all your worksheets and have a good day everyone! 

The next scriber will be..... ARI5 ! =)   

hey guys ok so i'm going to be doing the blog post for the past few classes since i forgot to do it last week =\.

ok so to begin,

by examining the change in amount of substance at a particular time or over a period of time, the rate of reaction can be determined. The representation of such a reaction may be seen as the following once recorded onto a graph:














In order to calculate the rate we would use the formula:
RATE =

(final concentration of A) - (initial concentration A)
__________________________________

final time - initial time

- OR -

RATE = [A]final - [A]initial

_________________________

[t]final - [t]initial

INSTANTANEOUS RATE: of a reaction at a specific time is determined by calculating the slope of the line tangent to the point on the concentration vs time curve.

We also learned two types of reactions, exothermic and endothermic.

EXOTHERMIC: the product possess less energy than the reactants, during the reaction heat is lost from the system and (delta)H is a negative value.

ENDOTHERMIC: the product possess more potential evergy than the reactants, this energy is absorbed from it's surroundings, increasing the system's energy content, giving a positive (delta)H value.

ok so thats pretty much what we have been duscussing, on monday Mrs. Kozoriz, wasn't there but the sub gave two worksheets one we finished in class (reaction rate 52; CHANGE IN H2O0 WITH TIME) and one we had to work on for the rest of the class (reaction rate 17; A model for reaction rates).

THE NEXT SCRIBE WILL BE........... hm........ lucky : *****Niwatori-san******

Monday November 3/08

HEY everyone!!!
I am truely sorry about the very late post, my internet was down and i couldnt do anything last night. ANYWHO,
Yesterday in class, was just a work period. We had to finish the analysis from the lab. And if you haven't done the lab yesterday was the chance.
Ms.k gave us a word search to do if we were done.
either than that, i don't really know what to right because it was just a work period.

Sorry Ms.K, i know you dont like these kinds of blogs, but i dont know what to write. (or in this case type)

christine will be be the next blogger =)

Experiment: Part I

Hello there!!

Okay, so what we did today is the experiment:

Factors affecting the rate of a reaction.
Materials:
24-well test plate
HCl Solution
Water
Zinc Nitrate Solution
Iron Nitrate Solution
Acetic Acid
Copper Nitrate Solution
Toothpicks

And a few pieces of the following:
Magnesium
Aluminum
Zinc
Copper
Iron

Part I:
1.) Add 20 drops of 3.0 moL/L HCl Solution to each of five wells of the 24-well test plate.
2.) Place a small piece of Mg in the first well, a piece of Al in the second, a piece of Zn on the third, a piece of Fe in the fourth, and a piece of Cu in the fifth.
3.) Observe and Record your observations.
Questions:
1.) What gas is produced? How do you know?
2.) Write a balanced equation to represent the reaction.
3.) Do all the metals take the same time to react?
4.) Rank all the metals in order of reactivity.
4.) Add 13 drops of water and 7 drops of 3.0 mol/L HCl solution to one well. Use the toothpick to stir the solution.
5.) Add 13 drops of water and 7 drops of 3.0 mol/L Acetic Acid to a second well. Stir.
6.) Add 20 drops of 1.0 mol/L aqueous Zn(NO3)2 solution to a third well, 20 drops of 1.0 mL/L Fe(NO3)3 to a fourth well, and 20 drops of 1.0 mL/L Cu(NO3)2 to a fifth well.
7.) Place a small piece of Mg in each of the five solutions.
8.) Observe and Record your observations.
Questions:
1.) What happened in each test tube? I dentify the products in each case.
2.) Write a balanced equation to represent each reaction.
3.) How much time does the Mg take to react in each solution?

The next blogger is Angela!

Atomic Structure Test

Atomicstrucutretest

View SlideShare document or Upload your own.

The Review..."Ëlectrons in Atoms"

Hola !!! hello everyone!!! this is Maria scribing for Tuesday's class.... This will be a short recap for the review on the test tomorrow.

Light and Quantized Energy

>Electromagnetic radiation. is a kind of ENERGY that behaves like a(n) WAVE as it travels through space.
--- Light is one type of electromagnetic radiation, others ex. include: X rays,
All waves can be characterized by their wavelength, amplitude, frequency,and speed.
>Wavelength.. is the shortest distance between equivalent point on a continuous wave.
>Amplitude.. is the height of a wave from the origin to a crest or from the origin to a trough.
>Frequency.. is the no. of waves that pass a given point in 1 second.





the photo shows the wavelength and the amplitude.






---A (n) Quantum is the minimum, amount of energy that can be lost or gained by an atom.---

Quantum Theory and the Atom.

1. Ground State. the lowest allowable energy state of an atom.

2. Bohr's Model of the atom predicted the FREQUENCIES of the lines in hydrogen's atomic emission spectrum.
3. According to Bohr's atomic model. >the smaller an electron's orbit, the lower the atom's energy level.
4. Also the larger an electron's orbit, the higher-energy orbit.
5. Bohr proposed that when energy is added to a hydrogen atom, it's ELECTRON moves to a higher- energy orbit.
6. ---- the hydrogen atom emits a photon corresponding to the difference b/w the ENERGY LEVELS associated w/ the 2 orbits transitions b/w.
7. Bohr's atomic model failed to explain the atomic emission spectrum of elements other the Hydrogen.


ex. Bohr's atomic model

QMM (Quantum Mechanical Model ). the modern model of the atom that treats electrons a waves.
Atomic Orbital. a three-dimensional region around around the nucleus representing the probability of finding an electron.

The difference b/w Bohr model and QMM(Quantum Mechanical Model ).
QMM treats electrons as waves and does not describe the electrons paths around the nucleus.
Bohr model treats electrons as particles traveling in specific orbits.














Electron Configurations
>The arrangement of electrons in an atom < style="color: rgb(204, 102, 204);">Ground-State Electron Configuration.
--3 Rules define how electrons can be arranged in an atom's orbital.--
Aufbau Principle. states that each electron occupies the lowest energy orbital available.
Pauli Exclusion Principle. states that a maximum of 2 electrons may occupy a single atomic orbital, but only if the electrons have opposite SPINS.
Hund's Rule. states that a single electrons with the same spin must occupy each equal-energy orbital before additional electrons w/ opposite spins occupy the same orbitals.


Well folks good luck on tomorrows test!!! the next blogger will be...............

• NCC-74656 Intrepid Class...

Electronegativity worksheets.

Hello Everyone! 

In todays wonderful chemistry class we worked on the three worksheets that we had to do over the weekend! 

Just in case you missed out on some of the questions, here are the answers : 

Worksheet 1 : Determining Electronegativity difference and Percent Ionic Character. 

1. a) 2.23 b) 1.27 c) 0.58 d) 1.26 e) 0.68

2. (A) Na and Cl would be considered ionic. 

3. % ionic character, electronegativity difference - direct relationship 

4. a) 70% b) 36% c) 10% d)33% e)12% 

5. ionic percent + covalent percent = 100 

6. a) 30% b) 65% c) 90%  d) 67%  e) 88%

Worksheet 2: Section 6.3 Periodic Trends 

1. (C) 2. (C) 3. (D) 4. (B) 5. (A)  6. (A) 

7. Ionization energy is the energy required to remove an electron from a gaseous atom. 

8. A high ionization energy value is not likely to form a positive ion because it has a strong hold on its electrons. 

9. first ionization energies increase as you move from left to right across a period because as you go across the period, the nucleus hold on to its electrons more tightly. 

10. In a group, first ionization energies decrease as you move down a group. This decrease in energy happens because atomic size increase as you move down the group. The valence electrons farther from the nucleus, less energy is required to remove them. 

11. * don't have. 

12. It indicated the relative ability of its atoms to attract electrons in a chemical bond. 

13. Electronegativy increase as you move from left to right across a period and decrease as you move down a group. 

Worksheet 3: Section 9.5 Electronegativity and Polarity

1. Its the ability to attract electrons in a chemical bond. 

2. Fl,  3.98,  Halogens,  group VII A 

3. Fr,  0.7,  Alkali metals,  group I A 

4. Group -> decreases Period -> increases 

5.  > 1.70 = ionic bond  < 70 =" covalent">

6. True

7. False 

8. (C) 9. (D) 10. (B) 11. *don't do*  12. (C) 13. (B)

14, 15, 16, 17.  *don't do* 

Here are the answers to our awesome and fun worksheet! =) 

After going over the worksheets we got a review that is needed to be done by tomorrow! 

Make sure that everyone studies because the test will be on WEDNESDAY, OCTOBER 22 2008! 

GOOD LUCK EVERYONE! =) 

next scribe is...  M