Factors affecting rxn rates

#3

http://www.youtube.com/watch?v=5tFy9bOLsxw

Iron Combustion!

Increasing the Rate of Reactions1. Increasing temperature

2. Increasing reactant concentration

3. Adding a catalyst (an inhibitor decreases) triggers a reaction rate to increase; participates in the reactions but comes out the same way it went in.

4. Nature of the reactant (changing a reactant for a more reactive one)

5. Increasing the pressure

6. Increasing the surface area – only for heterogeneous rxns!

same- only look at reactants!

AgNO3(aq) + NaCl(aq) →

H2(g) + O2(g) →

A homogeneous reaction is one where all the reactants are in the same phase. They are fast due to thorough mixing and many collisions!

Homogeneous Vs Heterogeneous Reactions

Fe(s) + O2(g) →

Zn(s) + 2HCl(aq) →

Heterogeneous reactants are in two or more different phases

Factors that Affect the Reaction Rate

Slow due to poor mixing and fewer collisions

Classify as Homogeneous or Heterogeneous:

                                         3.                   H2(g)    +  F2(g)        →              2HF (g)                                                                                    

 

                                

              2.                   Ag+ (aq)  +  Cl (aq)          →       AgCl  (s)                                                          

                                         

heterogeneous   1.  Zn (s)  +  2HCl (aq)       →       H2(g)  +  ZnCl2  (aq)        

homogeneous   

homogeneous   

  

What reactions are faster? ( in general )

1. Homo’s are faster than hetero’s.

2. Fastest Slowest

(aq) (g and l) (s) only reactants

3. Simple ionic are fastest -no bonds to break- double replacement

AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)

Ag+ + NO3- + Na+ + Cl- → AgCl(s) + Na+ + NO3

-

Ag+ + Cl- → AgCl(s)

simple ionic!

Becomes:

Fast

Fast

3H2(g) + N2(g) 2NH3(g)

2NaClO3(aq) + F2(aq) → 2NaF(aq) + 3O2(g) + Cl2(g)

HomoHomos are fast- more collisionsAqueous reactions are fasters than gaseous.

Describe each Pair of reactions as faster or slower.

Homo

Faster

Describe each Pair of reactions as faster or slower.

Zn(s) + 2HCl(aq) H2(g) + ZnCl2(aq)

C(s) + O2(g) CO2(g)

Hetero

Hetero

Faster because aq ions: 1. close proximity in soln 2. ability to move through solvent 3. strong +/- interactions.

5. Agitate

4. Increase surface area (powder Mg)

3. Add a catalyst

2. Increase [HCl], add more Mg

1. Increase temperature

Mg(s) + 2HCl(aq) → H2(g) + MgCl2(aq)

State five ways to increase the rate of this reaction.

Hebden, p 7. Exercises 10 – 11; p 8. Exercises 12 – 14; p 9. Exercises 15 – 16 AND 17.

(Read page12 on Collision Theory to fill in the blanks for tomorrow’s lecture)