Lecture 26: Addition Reactions and Chemical Kinetics

Addition Reaction

  • Takes place on a double bond
  • Electrophile to C==C


Halogens


Chemical Kinetics

Reaction Rates - Measure how quickly they proceed in a given time. The speed of a chemical reaction is usually reported as its change in concentration (molarity) over time, molarity per second (M/s)

Average rate of appearance of B=change in [B]change in time=Δ[B]ΔtB = \frac{change \ in \ [B] }{change \ in \ time} = \frac{\Delta [B]}{\Delta t}

Average Rate of Disappearance of A=change in [B]change in time=Δ[A]ΔtA = \frac{change \ in \ [B]}{change \ in \ time} = - \frac{\Delta[A]}{\Delta t}

  • Decreases and converts to BB


Relative Reaction Rate Equations - ΔBΔt, Δ[A]Δt\frac {\Delta B}{\Delta t}, \ \frac {\Delta [A]}{\Delta t}

*Rate of reaction decreases as the reaction proceeds because as the reaction proceeds, the amount of reactants decreases.


Overall Equation - For reaction: 2HI(g)H2(g)+I2(g)2HI_{(g)} \rightarrow H_{2(g)} + I _ {2(g)}

12Δ[HI]Δt=Δ[H2]Δt=Δ[I2]Δt- \frac{1}{2} \frac{\Delta [HI]}{\Delta t} = \frac {\Delta [H_2]}{\Delta t }= \frac {\Delta [I_2]}{\Delta t}

aA+bBcC+dDaA + bB \rightarrow cC + dD

1aΔ[A]Δt=1bΔ[B]Δt- \frac{1}{a} \frac{\Delta [A]}{\Delta t} = - \frac{1}{b} \frac {\Delta [B]} {\Delta t}=1cΔ[C]Δt=1dΔ[D]Δt= \frac{1}{c} \frac{\Delta [C]}{\Delta t} = \frac{1}{d} \frac {\Delta [D]} {\Delta t} 

Relationship between the rate and specific concentration is presented by the reaction order of a particular substance.

If doubling the concentration of one reactant \Rightarrow Rate doubles

== First order Reaction

If doubling the concentration and the rate quadruples

==  Reaction is Second Order

If it doesn't effect the rate, it is ==  zero order

The overall Reaction order is the sum of the orders from the individual reactants ==  if a reaction is first order with respect to each reaction it is overall second order


Rate Law

aA+bB+cCdD+eEaA + bB + cC \rightarrow dD + eE

rate =K[A]m[B]n[C]p= K[A]^m [B]^n [C]^p

m=m= order with respect to AA (ma)( m \neq a)

Not the coefficient from the equation. mm is expressed


Experimentally,

Initial Rates Data - Experimental technique to find m/n/pm/n/p by changing the initial concentrations of one reactant at a time then we can see the effect of one reactants concentration on the rate.


K=K =  rate \cdot constant (units)

First Order - 1/s1/s

Second Order - 1/(sm)1/(s \cdot m)

ZERO Order - m/sm/s


Integrated Rate Laws





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