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 ! =)   

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

chem. 09/08/08

Today in chem. class we learned something new, aqueous reactions.

Most of today's lesson consists of precipitation reactions.

Ms. K showed us how ionic compounds when put into water, dissolve.

When you have a solution that involves a chemical change in color, heat, odor and gas forming are usually called precipitating reactions. ( double displacement reaction, when two aqueous solutions are mixed ) Chemical reactions are occurring

I think we went over a little bit on net ionic equations and spectator ions.

She also showed how the certain chemicals moving together.

I think it was lead and nitrate ions moving around in the beaker and when the iodide and potassium was added with the lead and nitrate ions, it first moved randomly all around. Then iodide and lead started to form a big cluster of ions. Once it got big enough, the particles started to sink to the bottom. This was the part where you can notice substances floating on the bottom.

Tomorrow we're all going to start on a lab assignment on developing solubility rules. It to see if certain chemicals create a precipitation reaction or not.

I think i can remember certain things being said in today's lesson. I know for sure that my last year chemistry teacher went over this because i have already did this lab before. ( if its the same one I'm thinking about)

Well that's all i can remember from today's class.

Alvina