Kaplan MCAT: Gen Chem 2

Reaction Rate

Change in a property per unit time

 

 

Rate= Change in concentration

        time change to occur

Rate Laws

Rate= k [A]x[B]y

 

exponents (x,y)- orders of reaction; x is the order with respect to A and y is the order with respect to B. 

 

Overall reaction order=x+y

Equilibrium expresssion for….

 

H2 (g) + Cl2 (g) <—> 2HCl (g)

Equilibrium constant is Products over reactants, with order taken into account.

 

 

Kc=     [HCl]2  

      [H2][Cl2]

Le CHatelier’s Principle

When a stress is applied to a system at equilibrium, the system will adjust to minimize the effect of stress

;

eg.

;

N2 + 3H2 ;—->  2NH3 (g)

 

—what direction would equilibrium shift if additional N2 is added?

 

  would shift towards products (shift right, favoring the production of NH3)

Le Chatlier’s principle applied to temperature change

 

 

A<—-> B + heat

 

 if this system were cooled (eg. placed in an ice bath), which way would the reaction be driven?

the rxn. temp would decrease, driving the reaction towards products, to replace the lost heat.

 

If it were heated in boiling water, the rxn would shift left due to increased heat concentration.

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